Reviewers: N/A
Editor: Billo Heinzpeter Studer

Initial release: 2018-02-15
Version information:

• Appearance: B
• Last minor update: 2021-07-17

Cite as: »Volstorf, Jenny. 2021. Oncorhynchus mykiss (Dossier). In: fair-fish database, ed. fair-fish. World Wide Web electronic publication. First published 2018-02-15. Version B | 1.1. https://fair-fish-database.net.«

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• Unpredictable influence:
  • WILD: FRY (from wild-caught Steelhead trout eggs) in 1.8 diameter circular tanks and enriched with tops of two firs, cobbles in two wire shopping baskets (34 x 48 x 15 cm), underwater feed delivery system, overhead cover of camouflage netting on PVC frame or without enrichment (treatment types). After two months, behaviour observations in 90-215 m² enclosures in Eleven and Twelve Creeks, Washington, USA by stocking wild-caught FRY at 0.27 IND/m² together with either FRY from enriched or barren tanks at density 2 IND/m². After one week, higher aggression in wild-caught FRY paired with FRY from barren than from enriched tanks (1 versus 0.3 aggressive acts/min/IND). By week 4, reverse result (0.7 versus 0.4 aggressive acts/min/FRY). Higher foraging rate in wild-caught FRY paired with FRY from barren than from enriched tanks (2.5 versus 1.7 feeding strikes/min/IND). Results indicate higher impact on wild FRY by FRY raised in enriched than barren tanks, but effects in SMOLTS and long-term effects unknown 1.
  • WILD: >90% of released JUVENILES (Rainbow trout) left release site (North Channel of Lake Huron, Canada) for at least 24 h during first three weeks. 18% never returned, 82% returned after 1-102 d. Higher site fidelity when released in July than when released in May. Around one third recaptured within 500 m, another third within 5 km. Greatest dispersal 360 km. Survival after around three months: 52%, with highest mortality due to angling 2.
• Competition:
  • WILD: hatchery-reared Steelhead SMOLTS were released into wild (Teanaway river, Washington, USA). Paired in enclosures of 91 x 99 cm, 91 cm deep with either 40% smaller resident wild Rainbow trout JUVENILES or 100% smaller wild O. tshawytscha juveniles in one chamber of 0.46 m²; single wild Rainbow trout JUVENILES or O. tshawytscha juveniles in other chamber served as control. After 42 days, larger decrease in specific growth rate in wild Rainbow trout JUVENILES paired with hatchery-released Steelhead than in single wild O. mykiss (-0.002-0.004 versus -0.006). No difference in paired and single wild O. tshawytscha 3.
  • WILD: hatchery-reared Steelhead SMOLTS were released into wild (Teanaway river, Washington, USA). No difference in threatening, crowding (moving laterally in order to displace), butting (mouth closed) in interactions with wild conspecifics (Steelhead and Ranbow trout) compared to control streams but lower amount of chasing and higher amount of nipping (mouth open). Hatchery-reared Steelhead SMOLTS were bigger and initiated 61% of interactions with wild conspecifics and dominated in 68% of them. Tendency of more displacements from preferred microhabitats compared to control streams (79% versus 68%) and more displacements of wild by hatchery-reared then of hatchery-reared by wild (79% versus 58%) 4.
• Disease transmission: no data found yet.
• Interbreeding: breeding with native populations could reduce fitness and productivity in hybrids (because of the smaller genetic variability in farmed individuals) and eventually survival:
  • Observations WILD: varying amount of hybridisation between O. mykiss and O. clarkii lewisi: Flathead river, British Columbia, Canada and Montana, USA (introduced) 5.

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• For feeding ➝ 6 7.
• For daily rhythm ➝ 6 8 9 7.
• For migration ➝ 6 10 11 12 13.
• For redd construction, spawning ➝ 6.
• For schooling, shoaling ➝ 6 8.
• For social behaviour ➝ 4.
• For aggression ➝ 4 1.
• For territoriality ➝ 1.

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daily rhythm, swimming, social behaviour, cognitive abilities, coping styles, stress reactions

• For feeding ➝ 14.
• For daily rhythm ➝ 15.
• For swimming ➝ 16 17 18.
• For dominance and subordination ➝ 19 14 20.
• For aggression ➝ 19 14 21 20.
• For territoriality ➝ 14 20.
• For learning ➝ 22 23.
• For coping styles ➝ 24 22 21.
• For observable stress reactions ➝ 25 22 23 26.

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• Observations North America: Big Lost river, Idaho, USA 9, Bridge river, British Columbia, Canada 7, Cherry Creek, Oregon, USA 9, Eleven and Twelve Creeks, Washington, USA 1, Mokelumne river, California, USA 12, Pacific, North America 10, Parsons Creek, Idaho, USA 9, Santa Ynez river, California, USA 28, Scott Creek Watershed, California, USA 13, Sevenmile Creek, Oregon, USA 9, Silver Creek, Idaho, USA 8, Skookumchuck river, Washington, USA 14, Teanaway river, Washington, USA 3 4, Waddell Creek, California, USA 6.

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• Observations North America: Flathead river, British Columbia, Canada and Montana, USA 5.
• Observations New Zealand: lake Coleridge, New Zealand 11, lakes of the Rotorua district, New Zealand 29, lake Taupo, New Zealand 30.

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• Observations Bridgelip sucker WILD: Catostomus columbianus:  Silver Creek, Idaho, USA 8 (Rainbow trout), Teanaway river, Washington, USA (Rainbow and Steelhead trout) 3.
• Observations Brown trout WILD: Salmo trutta: Silver Creek, Idaho, USA 8 (Rainbow trout), lake Coleridge, New Zealand (introduced; Rainbow trout) 11.
• Observations Chinook salmon WILD: Oncorhynchus tshawytscha: lake Coleridge, New Zealand (introduced; Rainbow trout) 11.
• Observations (Eastern) Brook trout WILD: Salvelinus fontinalis: Silver Creek, Idaho, USA 8 (Rainbow trout), Teanaway river, Washington, USA (Rainbow and Steelhead trout) 3.
• Observations Longnose dace WILD: Rhinichthys cataractae:  Silver Creek, Idaho, USA 8 (Rainbow trout), Teanaway river, Washington, USA (Rainbow and Steelhead trout) 3.
• Observations Mountain whitefish WILD: Prosopium williamsoni:  Silver Creek, Idaho, USA 8 (Rainbow trout), Teanaway river, Washington, USA (Rainbow and Steelhead trout) 3.
• Observations Sculpin WILD: Cottus aleuticus, C. asper, Leptocottus armatus: Waddell Creek, California, USA (Steelhead trout) 6, C. leiopomus: Silver Creek, Idaho, USA 8 (Rainbow trout), C. confusus, C. rhotheus: Teanaway river, Washington, USA (Rainbow and Steelhead trout) 3.
• Observations Starry flounder WILD: Platichthys stellatus: Waddell Creek, California, USA (Steelhead trout) 6.
• Observations Striped bass WILD: Roccus saxatilis (introduced): Waddell Creek, California, USA (Steelhead trout) 6.
• Observations Three-spined stickleback WILD: Gasterosteus aculeatus: Waddell Creek, California, USA (Steelhead trout) 6.
• Observations Tidewater goby WILD: Eucyclogobius newberryi: Waddell Creek, California, USA (Steelhead trout) 6.
• Observations Top smelt WILD: Atherinops affinis: Waddell Creek, California, USA (Steelhead trout) 6.

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• Plants:
  • WILD (Rainbow trout): dense beds of macrophytes Chara vularis and Potamogeton pectinatus on 55-74% of stream bed from bank to bank: Silver Creek, Idaho, USA 8.
  • WILD: ADULTS rested in "tunnels" in Chara macrophyte beds: lake Coleridge, New Zealand (introduced; Rainbow trout) 11.
  • FARM: eyed embryos (Steelhead trout) in 1,520 L circular tanks with diameter 1.8 m and enriched with tops of Douglas firs (encompassing ca 21% water volume), underwater feed delivery system, 60% overhead cover of double layer camouflage netting on PVC frame or without enrichment (treatment types). After two months, habitat use observations in 5 m long x 3 m wide sections of outdoor stream channel with 3-5 cm diameter gravel, two tops of Douglas fir trees, and red alder log adjoined with equally sized section without enrichment so that FRY could swim freely between them. After 72 h, door between adjoining sections closed. No difference in habitat use between FRY when in groups from same treatment type (51.6-52%) or in groups of mixed treatment type (59.2-60.1%) 14.
• Rocks and stones:
  • WILD: FRY (from wild-caught Steelhead trout eggs) in 1.8 diameter circular tanks and enriched with tops of two firs, cobbles in two wire shopping baskets (34 x 48 x 15 cm), underwater feed delivery system, overhead cover of camouflage netting on PVC frame or without enrichment (treatment types). After two months, behaviour observations in 90-215 m² enclosures in Eleven and Twelve Creeks, Washington, USA over gravel and cobble substrate by stocking wild-caught FRY at 0.27 IND/m² together with either FRY from enriched or barren tanks at density 2 IND/m². No difference in territory size, aggression, and foraging rate between FRY from enriched and barren tanks 1.
  • WILD: JUVENILES-ADULTS (Steelhead trout) were found over large rubble and boulders but also gravel and small rubble beds: Waddell Creek, California, USA 6.
  • WILD (Rainbow trout): fine gravel on channel grounds through macrophyte beds: Silver Creek, Idaho, USA 8.
  • WILD: ADULTS (Rainbow trout) were found over cobble-boulder substrate: Cherry Creek, Oregon, USA 9.
  • For substrate and redd construction ➝ D1.
• Sand and mud:
  • WILD (Rainbow trout): 14 cm silt to sand under beds of macrophytes: Silver Creek, Idaho, USA 8.
• Other substrate: no data found yet.

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• FARM: FRY (Rainbow trout) in raceways 7 x 0.9 x 0.6 m with cobblestones (2-4 cm) and pea-size stones to fill interstitial spaces. After six months, less fin erosion than in control group without substrate (ca 5 versus 6 fin score) where 0 = perfect fin, 1 = slight erosion, 2 = severe erosion. Higher fin length in caudal, adipose, anal, right pectoral, right ventral, and left ventral fin. Shorter dorsal fin probably due to fin-nipping already at beginning of experiment. No difference in mortality (3.2-4.3%) 31.

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• Direct effect:
  • FARM: eyed embryos (Steelhead trout) in 1,520 L circular tanks with diameter 1.8 m and enriched with tops of Douglas firs (encompassing ca 21% water volume), underwater feed delivery system, 60% overhead cover of double layer camouflage netting on PVC frame or without enrichment (treatment types). After 2.5 months, either stocked in 5 m long x 3 m wide sections of outdoor stream channel with 3-5 cm diameter gravel, two tops of Douglas fir trees, and red alder log or in equally sized section without enrichment (habitat types). After 20 days, no difference in length and weight increases between FRY when in groups from same treatment type. When in groups of mixed treatment type, greater increases in length and weight in FRY from enriched than in FRY from barren tanks (1% versus 0.95% daily length increase, 4.1% versus 3.7% daily weight increase). No effect of habitat type, no interaction between treatment type and habitat type. Results indicate that enrichment increases competitive abilities (➝ D2) which in turn cause growth differences 14.
• No effect:
  • LAB: FRY (Rainbow trout) in raceways of 11 x 1.2 m, 0.6 m deep (2.8 m³) at ca 5 kg/m³ density, on day 34 increased to 5.7 m³ to accommodate fish growth, on day 51 increased to 6.8 m³. Raceways were lined with AquaMats, high-density polymers attached to reinforced plastic tarp, installed perpendicular to water flow at mat-to-volume ratios of 0.6-0.7:1 and either cleaned two times a week or not. After 93 days, no difference in final weights (34.3-35.6 g), specific growth rate (1.7%/day), FOOD CONVERSION RATIO (0.7). Tendency of higher cumulative mortality in uncleaned than cleaned group (1.4% versus 1.1%); control group without AquaMats in between (1.3%). Tendency of lower relative fin length for anal, left pelvic, and right pelvic fin in uncleaned versus control group; cleaned group in between. Could also be due to placement of AquaMats that separated segments of raceway and increased fish density between them. Alternatively, due to disease outbreak at two months into the study (cleared by hydrogen peroxide treatment).
    Experiment 2: FRY in raceways of 11 x 1.2 m, 0.6 m deep (2.8 m³) at ca 3.8 kg/m³ density, on day 47 increased to 4.4 m³. AquaMats installed parallel to water flow at mat-to-volume ratio of 1.7-1.9:1, not cleaned during study duration. After 106 days, no difference in final weights (31.8-32.1 g), specific growth rate (2.6%/day), FOOD CONVERSION RATIO (1.0-1.1), cumulative mortality (1.8-2.5%). Higher relative fin index for all fins of AquaMat-group on day 74, but only for left pectoral fin on day 106. Maybe beneficial effect was lost due to doubling of mat-to-volume ratio on day 47.
    Both experiments: despite of algal growth on the AquaMats and attached Chironomid larvae, FRY probably did not gain additional food from them 32.

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• Plants:
  • WILD: 0+ JUVENILES (Rainbow trout) concealed themselves in Chara vulgaris during the night and – beginning with temperatures below 8 °C in autumn (and through to end of observation period in January) – also during the day: Silver Creek, Idaho, USA 8.
  • WILD: in winter, ADULTS (Rainbow trout) were found in shallow pools with large woody debris (Big Lost river, Idaho, USA) or in deep pools with small (<10 cm diameter) woody debris (Parsons Creek, Idaho, USA) probably to hide from predators 9.
• Rocks and stones:
  • WILD: in winter, JUVENILES (Steelhead trout) were concealed between large boulders and cobble: Bridge river, British Columbia, Canada 7.
  • WILD: in winter, ADULTS (Rainbow trout) were found behind large boulders probably to hide form predators: Cherry Creek, Oregon, USA 9.
  • LAB: ALEVINS (Steelhead trout) emerged from gravel at 2-6 weeks after hatching 33-6.
• Sand and mud:
  • WILD: with temperatures below 8 °C in autumn (and through to end of observation period in January), 0+ JUVENILES (Rainbow trout) concealed themselves in silt and clay during day: Silver Creek, Idaho, USA 8.
• Other cover:
  • WILD (Rainbow trout): undercut or vertical banks at >90% of stream: Silver Creek, Idaho, USA 8.
  • WILD: ADULTS (Rainbow trout) were found at undercut banks: Big Lost river and Parsons Creek, Idaho, USA, Cherry Creek and Sevenmile Creek, Oregon, USA 9.
  • FARM: FRY (Rainbow trout) in 100 L tanks either covered to 33% or 66% by black plastic sheet or uncovered. After eight weeks, vigorous hand waving for 5 s over tank. FRY in covered tanks took retreat whereas FRY in uncovered tanks scattered. Afterwards, subsample taken and placed into tanks with all of three conditions, hand waving for 5 s. FRY used to cover, now placed in uncovered tanks, scattered; FRY used to cover, now placed in covered tanks, took retreat; FRY used to uncovered tanks, now placed in covered tanks, scattered 34.
  • FARM: JUVENILES (Rainbow trout) in 2 m diameter outdoor tanks, one half covered by solid top, did not display special preference for covered half 15.
  • For cover and confinement ➝ D3.

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• Observations: 4.1±0.3 se 35.

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• Carnivorous D4. The fishery that provides fish meal and fish oil has two major impacts:
  1. It contributes considerably to overfishing, as it accounts for 1/4 36 or even 1/3 37 of the world catch volume.
  2. It challenges animal welfare, because in the face of 450-1,000 MILLIARD wild fishes caught worldwide each year to be processed into fish meal or fish oil 38, the individual fish gets overlooked and, thus, suffering increases at rearing, live marketing, and slaughtering levels 39.

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• Food items: carnivorous:
  • Observations WILD, JUVENILES: mainly Bullies Gobiomorphus cotidianus, Smelt Retropinna retropinna, furthermore: aquatic insect larvae, Crayfish Paranephrops planifrons, adult terrestrial insects: lake Rotoma, New Zealand (introduced; Rainbow trout) 29, mainly benthic prey: Ephemeroptera larvae (Deleatidium spp., Coloburiscus humeralis), Diptera (larval and adult Chironomidae), Trichoptera (Hydrobiosis spp.), small Koaro Galaxias brevipinnis, eggs of O. mykiss: Waipehi and Omori stream, New Zealand (introduced; Rainbow trout) 30, mainly Mayflies Ephemerella inermis and Baetis sp., Chironomidae, other Ephemeroptera, other aquatic invertebrates, other Diptera, terrestrial invertebrates: Silver Creek, Idaho, USA (Rainbow trout) 8, mainly Diptera, Ephemeroptera, Hymenoptera, Coleoptera, Trichoptera: Teanaway river, Washington, USA (Rainbow and Steelhead trout) 3.
• Food items and habitat: no data found yet.
• Food items and life stages: no data found yet.
• Food preference: no data found yet.
• Food partitioning: no data found yet.
• Prey density: no data found yet.
• Prey size selectivity: no data found yet.
• Particle size: no data found yet.

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• WILD: ALEVINS (Steelhead trout) darted up to drift prey, rejecting those that are unsuitable, resumed position at bottom: Waddell Creek, California, USA 6.
• WILD, JUVENILES (Rainbow trout): higher frequency of pelagic Smelt Retropinna retropinna than benthic Bullies Gobiomorphus cotidianus in stomachs (44-62% versus 0-12%) in deep, clear, oligotrophic lakes; reverse (7-13% versus 28-63%) in shallow, turbid, eutrophic lakes of Rotorua district, New Zealand (introduced). Result indicates visual hunting that is hindered in eutrophic lakes and thus results in reduction of surface feeding 29.
• WILD: in summer, weight of food in stomach of 0+ JUVENILES (Rainbow trout) was correlated with surface drift, not with temperature (13-17.4 °C) or subsurface drift. In autumn, correlation with surface drift and temperature (9-12.5 °C). Daytime concealment from September 26th on. No indication of benthic feeding: Silver Creek, Idaho, USA 8.
• WILD: JUVENILES (Steelhead trout) actively foraged on drift organisms in stream: Bridge river, British Columbia, Canada 7.
• FARM: FRY (Steelhead trout) in 5 m long x 3 m wide sections of outdoor stream channel with 3-5 cm diameter gravel, two tops of Douglas fir trees, and red alder log or in equally sized section without enrichment. Daphnia were constantly introduced. Primarily picked up feed from substrate, only seldomly fed at surface 14.

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• FARM: all-female FRY (Rainbow trout) in 1 m³ tanks at 1 kg/m³ density were fed two times a day a total of 1% stock weight. Dorsal fin already eroded during acclimation period, so effect of feeding frequency on fin could not be evaluated. After 67 days, no difference in fin index. Individuals removed to achieve 7 kg/m³ density. Now fed three times a day a total of 2.9-3.5% stock weight. After 28 days, no difference in fin index among JUVENILES in this feeding frequency but decrease compared to previous feeding frequency mainly in pelvic (53% decrease), caudal (18% decrease), and anal fins (11% decrease). Possibly due to random fin biting during feeding which consequently happens more often when fed three than two times. Right pectoral fin 8% shorter than left one possibly due to clockwise flow in circular tank and higher risk of biting into right fin when feed is administered in center 42.

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• LAB: JUVENILES (Rainbow trout) in square 60 L tanks fed once a day either 2.0, 1.5, 1.0, or 0.5% body weight. After six weeks, higher haematocrit (45.7-46.8% volume versus 42.2% and 38.5%) and better fin condition (sum of fin conditions of dorsal and caudal fins at five measuring times where 1 = poor, 4 = excellent) under feeding ration of 2.0 and 1.5% body weight than under 1.0% and 0.5% (33.8-35.6 versus 31.6 and 26.8) indicating insufficient energy and nutrient intake and more food competition under 1.0 and 0.5% 16.

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• LAB: JUVENILES (Rainbow trout) in square 60 L tanks fed once a day either 2.0, 1.5, 1.0, or 0.5% body weight. After six weeks, lower specific growth rate the lower the feeding ration (1.8%/d at ration of 2.0% body weight, 1.4% at 1.5% body weight, 0.8% at 1.0% body weight, 0.1% at 0.5% body weight) indicating increasing competition for food 16.
• LAB, JUVENILES (Rainbow trout): higher specific growth rate in dominant than subordinate JUVENILES until 5% of wet weight dry food. No difference from next amount of 10% on which represented satiation (feed left on the bottom) (for details on the study ➝ D5) 20.

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• Feeding and temperature:
  • WILD, PARR (Steelhead trout): at lowest temperatures, December-February, feeding decreased, growth stopped: Waddell Creek, California, USA 6.
  • WILD, 0+ JUVENILES (Rainbow trout): when temperatures dropped below 13 °C, weight of food in stomach was correlated with temperature and decreased compared to summer, but JUVENILES did not cease feeding: Silver Creek, Idaho, USA 8.
• Feeding and spawning:
  • WILD: KELTS (Steelhead trout) after spawning did not resume feeding until they returned to sea which could be from days to months: Waddell Creek, California, USA 6.

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• Daily rhythm:
  • WILD, JUVENILES (Steelhead trout): predominantly nocturnal in lower reach with 16 m width, <1 m depth, hiding during day, leaving substrate at dusk; in upper reach (8 m width, <0.5 m depth), nocturnal in winter, visible in stream in afternoon in other seasons. Activity in afternoon inversely related to body size: FRY more visible than age 1 and age 2 PARR: Bridge river, British Columbia, Canada. Results indicate large variation within population and interaction between individuals and environment 7.
  • WILD (Steelhead trout): PARR and KELTS moved downstream predominantly at night or dusk or dawn, GRILSE moved upstream predominantly in daytime: Waddell Creek, California, USA 6.
  • WILD: higher densities of 0+ JUVENILES (Rainbow trout) in night than day in summer, autumn, and winter: 20.2-56.1 IND/100 m² at day versus 5.7-61.0 IND/100 m² at night in summer, 20.6-40.6 IND/100 m² versus 2.0-48.0 IND/100 m² in end of September, 0-14.8 IND/100 m² versus 0-1.4 IND/100 m² from October to January (end of observation period). Last date of observation of day-active JUVENILES was September 25th at 13 °C: Silver Creek, Idaho, USA 8.
  • WILD, ADULTS (Rainbow trout): higher fish count during night than day (ca 46 versus 21) in winter indicating concealment during day. Higher nocturnal index (proportion of fishes counted during night given all counted fishes) in colder rivers (ca 91% versus 59-75%): Big Lost river and Parsons Creek, Idaho, USA, Cherry Creek, Oregon, USA 9.
  • FARM: JUVENILES (Rainbow trout) in 2 m diameter outdoor tanks were stationary at night (only at density 28 kg/m³, not 80 or 136 kg/m³). Higher hourly distance moved during day than night (56-187 m/h versus 49-124 m/h), no clear pattern at other densities 15.
  • For velocity preference at night versus day ➝ D10.
• Nocturnal activity: ➝ Daily rhythm.
• Phototaxis: no data found yet.

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• LAB: JUVENILES (Rainbow trout) in 83 x 49 cm and 42 cm deep glass tanks at density 8.6 kg/m³ and either white, red (605 nm), or blue light (480 nm) at 150 lux. After 111 days, no difference in final weight (370.9-396.2 g), condition factor (1.36-1.42), specific growth rate (0.82-0.87%/d), weight gain (155.1-172.3%), and FOOD CONVERSION RATIO (1.57-1.69). Tendency of higher length under red light (30.7 cm versus 29.8-29.9 cm). Confirmed in additional study comparing 150, 300, and 600 lux for 150 lux only (unpublished results) 43.

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• Standard temperature range: 0-20.5 °C:
  • Observations WILD, JUVENILES-ADULTS: 45-58 °F (7.2-14.4 °C): Waddell Creek, California, USA (Steelhead trout) 6, SMOLTS-KELTS: at sea, 3-16 °C, 96% at ≤12 °C: Pacific, North America (Steelhead trout) 10, 7-15 °C: Waipehi stream, New Zealand (introduced), 9-14 °C: Omori stream, New Zealand (introduced; Rainbow trout) 30, range 4-17 °C, 0 °C on two days in January, no anchor but surface ice in January: Silver Creek, Idaho, USA (Rainbow trout) 8, 7-15 °C: lake Coleridge, New Zealand (introduced; Rainbow trout) 11, 7-20.5 °C: Teanaway river, Washington, USA (Rainbow and Steelhead trout) 3, 1.6-7.5 °C in winter: Big Lost river and Parsons Creek, Idaho, USA, Cherry Creek and Sevenmile Creek, Oregon, USA (Rainbow trout) 9.
• Temperature preference:
  • WILD: decreasing density of 0+ JUVENILES (Rainbow trout) with decreasing temperatures with sharp decline when temperatures dropped below <10 °C (for densities ➝ D12). Last date of observation of day-active JUVENILES was September 25th at 13 °C: Silver Creek, Idaho, USA 8.
  • WILD: increasing number of JUVENILES (Steelhead trout) visible in stream during day with increasing temperature (10+ °C), but only in shallower than deeper stream: Bridge river, British Columbia, Canada. Result indicates that behaviour is not just function of temperature 7.
• For temperature and...
  ...concealment ➝ D13,
  ...feeding ➝ D14,
  ...daily rhythm ➝ D15,
  ...velocity preference ➝ D10,
  ...depth ➝ D16.

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• Temperature must exceed: no data found yet.
• Temperature must not go beyond: no data found yet.
• Optimal temperature for growth: no data found yet.
• For temperature and growth ➝ D14.

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• Salinity tolerance:
  • Natural and introduced distribution in fresh water D17 D18 for the POTAMODROMOUS Rainbow trout. Distribution of the ANADROMOUS Steelhead trout in fresh water from egg to PARR stage and again as GRILSE, in between as SMOLTS in seawater D19.
• Standard salinity range: no data found yet.

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• Standard turbidity range:
  • Observations ultra-oligotrophic WILD: lake Coleridge, New Zealand (introduced; Rainbow trout) 11.
  • Observations eutrophic WILD: lakes of Rotorua district, New Zealand (introduced; Rainbow trout) 29.
  • For turbidity and feeding style ➝ D20.
• Secchi depth (water transparency):
  • Observations WILD, JUVENILES-ADULTS: 0.5-15 m: lakes of the Rotorua district, New Zealand (introduced; Rainbow trout) 29.

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• Swimming type: sub-carangiform:
  • Observations: for Rainbow trout 18, for Rainbow and Steelhead trout 44.
• Swimming and lateral line and vision:
  • LAB: in flow tanks with 5 cm D-section cylinder creating Kármán vortex street, JUVENILES (Rainbow trout) preferred to Kármán gait, i.e. positioned head in center 20 cm downstream from cylinder and displayed large amplitude body motions. Also when lateral line was pharmacologically blocked by exposing to 0.15 mmol/L cobalt hexachloride, although displayed larger variation in swimming behaviour. When blocking vision (turning off lights), JUVENILES preferred to entrain, i.e. positioned head at either side and downstream of the cylinder without axially undulating. Also when additionally lateral line was blocked, although entrained on just one side of the tank (for more details on lateral line blocking on swimming ➝ D21). Results indicate that vision has major role in swimming behaviour 17.
• For swimming and stocking density ➝ D22.

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• Absolute swimming speed:
  • Observations WILD: JUVENILES-ADULTS (Steelhead trout) migrated downstream with 0.01-4.11 km/h: Mokelumne river, California, USA 12.
  • Observations WILD, ADULTS: 0-0.2 km/h, up to 0.6 km/h on average (ca 0.3 body lengths/s), 2.3 km/h maximum swimming speed (1 body length/s): lake Coleridge, New Zealand (introduced; Rainbow trout) 11.
• Relative swimming speed:
  • LAB: JUVENILES (Rainbow trout) in square 60 L tanks fed once a day either, 2.0, 1.5, 1.0, or 0.5% body weight. After three weeks, swim trials started where individual JUVENILES were placed in respirometer with velocity increasing by 0.75 body lengths/s every 40 min until exhaustion. After six weeks, higher relative critical swimming speed under feeding ration of 2.0 and 1.0% body weight than under 0.5% (4.2 versus 3.4 body lengths/s), 1.5% in between (3.8 body lengths/s) 16.
• Swimming speed and temperature: no data found yet.

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• Standard velocity range:
  • WILD (Rainbow trout): 3-48 cm/s: Silver Creek, Idaho, USA 8.
• Velocity preference:
  • WILD, 0+ JUVENILES (Rainbow trout): mean focal velocity decreased with decreasing temperatures from 7-15 cm/s at 13 °C in August to 1-3 cm/s at 3 °C in January: Silver Creek, Idaho, USA 8.
• Velocity and temperature: no data found yet.
• For velocity and redd construction ➝ D1.

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• WILD: PARR (Steelhead trout) in first winter after hatching did not move downstream with floods but maintained position in stream: Waddell Creek, California, USA 6.
• WILD, SMOLTS-KELTS (Steelhead trout): seasonal movement northward and westward in spring and summer, southward and eastward in autumn and spring: in spring, at 42-52°N latitude along North American coast westward to 155°W longitude in Gulf of Alaska. In summer, mainly 42°N latitude to Alaskan and Kamchatkan coast (but up to 56°N) and 140°W-180° longitude. In autumn, mainly southern side of Aleutian Island chain into Gulf of Alaska (170°E to 140°W longitude). In winter, 44-58°N latitude and east of 135°W longitude 10.
• WILD, ADULTS (Rainbow trout): either large-scale movement within 33 km² lake Coleridge, New Zealand (introduced) – probably for feeding – or remained in bay where they were caught 11.

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• Depth range in the wild: 0.1-100 m:
  • WILD: ALEVINS (Steelhead trout) after emerging from gravel moved to shallow gravel areas at the side of the streams. Transferred to deeper waters with increasing age: Waddell Creek, California, USA 6.
  • WILD, 0+ JUVENILES (Rainbow trout): 61-73 cm across seasons. Mean 45 cm in August, moved deeper in September (mean 51 cm) when in aggregations. Moved shallower with decreasing temperatures, to 27 cm at end of observation period in January and closer to bottom at the same time: from 4-7 cm over substrate in August-November to <1 cm in January: Silver Creek, Idaho, USA 8.
  • Observations WILD, JUVENILES: 0.1-10 m after release from farm (Rainbow trout) 2.
  • Observations WILD, SMOLTS-KELTS: at sea in coastal water, 72% within 1 m en route to River Dean, British Columbia, Canda (Steelhead trout) 45-10.
  • Observations WILD, ADULTS: 0-10 m in winter-spring, up to 100 m in summer-autumn: lake Coleridge, New Zealand (introduced; Rainbow trout) 11.
  • For depth and redd construction ➝ D1.
• Depth in cages or tanks: no data found yet.
• Depth preference: no data found yet.
• Depth and daily rhythm: no data found yet.
• Depth and low temperatures: ➝ Depth and high temperatures.
• Depth and high temperatures:
  • WILD, JUVENILES (Rainbow trout): higher frequency (48-95%) caught in bottom than surface nets in summer, reverse (33-99%) in winter indicates avoidance of warmer surface layers when temperatures exceed 20-21 °C: lakes of the Rotorua district, New Zealand (introduced) 29.
• Position in habitat and age:
  • WILD: higher density of 0+ JUVENILES (Rainbow trout) in midchannel than in stream margin (with undercut banks) during day but vice versa during night: 5.7-25.0 IND/100 m² in stream margin versus 26.7-61.0 IND/100 m² in midchannel during day in summer, 32.4-56.1 IND/100 m² in stream margin versus 20.2-34.9 IND/100 m² in midchannel during night in summer, 2.0-5.7 IND/100 m² in stream margin versus 38.6-48 IND/100 m² in midchannel during day in end of September, 31.5-40.6 IND/100 m² in stream margin versus 20.6-23.3 IND/100 m² in midchannel during night in end of September. From October until January (end of observation period) 0-1.4 IND/100 m² during day in stream margin and midchannel, 2-15.8 IND/100 m² in stream margin versus 0-2.3 IND/100 m² in midchannel during night: Silver Creek, Idaho, USA 8.
• Depth and light intensity: no data found yet.
• Depth and noise: no data found yet.
• Depth and threat: no data found yet.

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• ANADROMOUS form (Steelhead trout):
  • ALEVINS, FRY, and PARR remain in streams and rivers for 1-4 years:
    • Observations WILD: FRY, age 1 and age 2 PARR: Bridge river, British Columbia, Canada 7.
    • WILD: PARR remained in fresh water for up to 4 years, performing upstream and downstream migrations: Waddell Creek, California, USA 6.
  • PARR migrate to the sea (sometimes via estuaries where they turn into SMOLTS) to mature, some return immature for another season:
    • WILD: of >400 JUVENILES tagged of hatchery or natural origin, >40% migrated downstream, >30% remained resident, 27% not detected. Of migrating, higher proportion of hatchery-reared SMOLTS than of natural origin (65% versus 22%): Mokelumne river, California, USA 12.
    • WILD: PARR migrated downstream to the estuary throughout the year, peaking in spring at 80-100 mm fork length. PARR (having begun to smolt) migrated upstream from lagoon in autumn when salinity increased (due to storm surges from Pacific) and dissolved oxygen decreased (due to freshwater algae death). Second downstream movement (now as SMOLTS) probably to the sea in February-March at 140-210 mm fork length: Scott Creek Watershed, California, USA. Results indicate that smoltification is variable and may adapt to environmental suitability 13.
    • WILD, SMOLTS: part of population (immature "half-pounders") returned to fresh water: Waddell Creek, California, USA 6.
    • WILD, SMOLTS: peak migration to sea (Pacific coastal waters of North America) in May. Part of population (immature "half-pounders") returned to fresh water before first winter at sea 10.
  • ADULTS return as GRILSE after 1-3 years to natal streams to spawn:
    • WILD: GRILSE began to enter streams after 1-3 years at sea in October-December with opening of sand bars at mouth of creek in beginning of rainy season; run continued to enter until May: Waddell Creek, California, USA 6.
    • WILD: after up to three years or more at sea, matured SMOLTS (now GRILSE) moved inshore from sea in summer and looked for spawning rivers 10.
  • Some return to the sea as KELTS and spawn again in streams:
    • WILD: some KELTS left to sea immediately after spawning, others remained in streams for months. Repeat spawners constituted 17.2% of individuals entering fresh water of which 15.0% were second spawners, 2.1% third spawners, 0.1% fourth spawners: Waddell Creek, California, USA 6.
    • WILD: after spawning, may return to sea as KELTS, mostly remained nearshore and in coastal waters 10.
• POTAMODROMOUS form (Rainbow trout):
  • ADULTS move upstream to spawn:
    • Observations WILD: moved upstream (into tributary) to spawn: lake Coleridge, New Zealand (introduced) 11.

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• Observations time from fertilisation until hatching WILD: 25-35 days: Waddell Creek, California, USA (Steelhead trout) 6.
• Observations time from fertilisation until hatching FARM: 50% hatched at day 34, 100% at day 36 (Steelhead trout) 46.
• Observations size: no data found yet.
• Observations weight FARM: mean 0.1 g, range 0.09-0.13 g (Steelhead trout) 46.

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• Observations age at yolk sac absorption FARM: ca day 28 (Steelhead trout) 46.
• Observations age at yolk sac absorption LAB: emerged from gravel 2-6 weeks after hatching and did not absorb yolk sac before it (Steelhead trout) 33-6.
• Observations length and weight LAB: 17-18 mm fork length and 0.1 g at hatching, 23-26 mm fork length and 0.2 g at time of emergence from gravel (Steelhead trout) 33-6.
• Observations weight FARM: 0.007 g at hatching (Steelhead trout) 46.

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• Observations age at beginning of exogenous feeding: after 2-6 weeks ➝ Larvae.
• Observations age, length, and weight WILD: age 0: 53-58 mm fork length, 2.0 g, 2.6 g: Bridge river, British Columbia, Canada (Steelhead trout) 7.
• Observations age and TOTAL LENGTH FARM: 3 months, 65 mm (Rainbow trout) 31.
• Observations weigth LAB: 1.7 g (Rainbow trout) 32, 13 weeks and 14 g (Rainbow and Steelhead trout hybrid) 47.

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• Juveniles (Rainbow trout): 0-3+ years, 49-240+ mm, 18.0-1,384 g:
  • Observations age, TOTAL LENGTH, and weight WILD: 2+: 311-470 mm fork length, 3+: 471-570 mm fork length: lakes of the Rotorua district, New Zealand (introduced) 29, 32-205 mm fork length: Waipehi and Omori stream, New Zealand (introduced) 30, 0+ JUVENILES: 49-122 mm: Silver Creek, Idaho, USA 8, 1+ or 2+ (back-calculated from size): 114.4-169.4 mm fork length and 18.0-51.0 g: Teanaway river, Washington, USA (Rainbow and Steelhead trout) 3.
  • Observations age, TOTAL LENGTH, and weight FARM: 24 cm, 147 g 49, 13 months, 250 g 15, 1 year, 344-434 mm fork length, 710-1,384 g 2.
  • Observations TOTAL LENGTH and weight LAB: 270 mm, 302 g 50, 11.1-11.3 cm standard length 25, 2 years, 120 g 19, 15.7 cm, 64.4 g 22, 22 months, 641 g 23, 12 months, 23.6 cm, 145 g 43, 133 mm and 48.6 g, 113 mm and 24.5 g 51, 100.8-107.9 g 21.
• Sexual maturity (Rainbow trout):
  • Observations age, TOTAL LENGTH, and weight males: no data found yet.
  • Observations age, TOTAL LENGTH, and weight females: no data found yet.
• Parr (Steelhead trout): 0-4 years, 80-100 mm fork length, 13.6-14.4 g:
  • Observations age: ➝ D19.
  • Observations age, length, and weight WILD: age 1: 13.6 g, 14.4 g: Bridge river, British Columbia, Canada 7, 80-100 mm fork length 13.
• Smolt (Steelhead trout): 1-7 years, 70-250 mm fork length, 59-73 g:
  • Observations age: ➝ D19.
  • Observations length  WILD: mean 110 mm and range 70-250 mm fork length: Scott Creek Watershed, California, USA 13.
  • Observations length and weight FARM: 177-199 mm fork length, 59-73 g 4.
  • Observations weight: no data found yet.

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• Grilse (Steelhead trout):
  • Observations age, length, and weight WILD: first time spawners: 2-7 years, males 38.5-79.5 cm fork length, females 40.2-79.5 cm fork length: Waddell Creek, California, USA 6.
• Kelt (Steelhead trout):
  • Observations age, TOTAL LENGTH, and weight: no data found yet.
• Rainbow trout:
  • Observations age, TOTAL LENGTH, and weight WILD: 4-7 years, 440-590 mm, 1,100-2,100 g: lake Coleridge, New Zealand (introduced) 11.

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• Observations WILD: PARR (Steelhead trout) until 2 years of age most likely distributed 1:1: Waddell Creek, California, USA 6.

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• Growth and dam:
  • FARM, ADULTS (Steelhead trout): dam influenced fertilisation, mortality from fertilisation to eyed-embryo stage and from eyed-embryo stage to hatching, hatchability, body weight, percent yolk at hatching and emergence, duration of emergence period, growth from 40 to 52 days post fertilisation, length of time to 50% yolk, yolk absorption from 40 to 52 days post fertilisation 46.
• Growth and sire:
  • FARM, ADULTS (Steelhead trout): sire influenced time to 50% emergence and yolk conversion efficiency from 40 to 52 days post fertilisation 46.

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• WILD, JUVENILES-ADULTS (Steelhead trout): individuals with atrophied or partially missing fins were rarely observed and if so, more among ADULTS than JUVENILES pointing to injuries happening at sea. Occasionally deformed upper or lower jars: Waddell Creek, California, USA 6.
• WILD/FARM: linear relationship between fin and TOTAL LENGTH in wild-caught JUVENILES (Rainbow trout). Shorter dorsal, caudal, anal, pectoral, and ventral relative fin lengths (fin length * 100 / TOTAL LENGTH) in hatchery-reared compared to wild-caught JUVENILES. Most severe erosion in dorsal and pectoral fins. Adipose fin longer in hatchery-reared 52.

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• Redd construction and substrate:
  • Observations WILD, ADULTS (Steelhead trout): medium and small gravel: Waddell Creek, California, USA 6.
• Redd construction and water velocity:
  • Observations WILD, ADULTS (Steelhead trout): usually at head of riffle, also at end of pool so that current washes out incoming silt with floods that otherwise restrict oxygen supply to eggs: Waddell Creek, California, USA 6.
• Redd construction and water depth:
  • Observations WILD, ADULTS (Steelhead trout): where surface water "breaks" into the riffle, ca 5 inches (ca 12.7 cm): Waddell Creek, California, USA 6.
• Redd construction:
  • WILD, ADULTS (Steelhead trout): female chose site and digged pit by laying on side and moving tail to swirl up substrate to round depression of 4 inches-1 foot (10.2-30.5 cm) depth and 15 inches (38.1 cm) diameter. Whole of 6-7 pits encompassed 12 feet (3.7 m) long, 5 feet (1.5 m) wide (60 square feet; 5.6 m²) and constituted redd: Waddell Creek, California, USA 53-6.

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• Courtship sequence:
  • WILD, ADULTS (Steelhead trout): while female built nest, male held position downstream of her, changing sides to stimulate her. When approached closely, one or both of them quivered. Male divided time between chasing attending males that held positions in an arc downstream and stimulating female by rubbing snout over and under her tail: Waddell Creek, California, USA 53-6.
• Courtship duration: no data found yet.

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• Monogamy:
  • WILD, ADULTS (Steelhead trout): temporary pair bond: one male among those that accompanied female in redd construction (without digging) rushed other attending males away: Waddell Creek, California, USA 53-6.
• Polygyny:
  • WILD, ADULTS (Steelhead trout): one male is believed to court more than one female: Waddell Creek, California, USA 6.

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• Spawning substrate: ➝ D1.
• Spawning season: October-December until summer:
  • Observations WILD: beginning October-December until May: Waddell Creek, California, USA (Steelhead trout) 6, summer (Steelhead trout) 10.
• Spawning (day)time: no data found yet.
• Spawning temperature: no data found yet.
• Spawning salinity: fresh water ➝ D19 D1.
• Spawning and water velocity: ➝ D1.
• Spawning depth: ➝ D1.
• Spawning density: no data found yet.

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• Male:female ratio resulting in spawning:
  • Observations WILD, ADULTS: 1:1.05: Waddell Creek, California, USA (Steelhead trout) 6.
• Composition of broodstock: no data found yet.

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• Spawning sequence:
  • WILD, ADULTS (Steelhead trout): female lowered anal fin and vent into pit, male close to her in opposite direction. Both released eggs and milt simultaneously: Waddell Creek, California, USA 6.
• Spawning duration:
  • WILD, ADULTS (Steelhead trout): few seconds per spawning, releasing all eggs over all pits in 12 h to a week or more: Waddell Creek, California, USA 6.

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• Number of pits:
  • Observations WILD, ADULTS: 6-7 pits per female representing one redd: Waddell Creek, California, USA (Steelhead trout) 6.
• Fecundity per pit:
  • Observations absolute fecundity WILD, ADULTS: 550-1,300 eggs per pit, resulting in 3,800-7,800 eggs distributed over 6-7 pits per female: Waddell Creek, California, USA (Steelhead trout) 6.
  • Observations relative fecundity: no data found yet.

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• Breeding type: gravel breeder:
  • WILD, ADULTS (Steelhead trout): after spawning, female covered pit immediately, digged other pits upstream to provide even more material for covering and depositing more eggs: Waddell Creek, California, USA 6.

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• LAB, JUVENILES (Rainbow trout): spectrophotometry of retina of dissected eyes yielded single cones either UV absorbing (365 nm) or blue absorbing (434 nm), double cones either green absorbing (531 nm) or red absorbing (576 nm), and rods (521 nm) 54.

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• For vision and swimming ➝ D28.

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• LAB: JUVENILES (Rainbow trout) reared in green tanks in farm were kept in 500 L stainless steel tank in laboratory. Light yellow 1 m² test tanks were divided into four compartments between which individually placed JUVENILES could move and covered with gelatin filters of either blue (435 nm), green (534), yellow (546 nm), or red colour (610 nm). 24 h lighting of 60 lux. During three days at 1 °C, higher visiting frequency in blue and green than in yellow and red compartments. During three days at 12 °C, higher visiting frequency in green compartment. Results indicate that colour preference changes with temperature.
  To test effect of colour of rearing tank, JUVENILES were kept in 40 x 20 x 25 cm aquaria covered with blue, red, yellow, green, or white canson paper on the side and gelatin filters of the same colour (or white paper) on top under 24 h lighting of 60 lux at 17 °C. After 42 days, JUVENILES reared in green, yellow, or red tanks preferred green; JUVENILES reared in blue tanks preferred blue and green. Results indicate that rearing colour influences colour preference 51.

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• LAB: JUVENILES (Rainbow trout) reared in green tanks in farm were kept in 500 L stainless steel tank in laboratory. 40 x 20 x 25 cm test aquaria covered with blue, red, yellow, green, or white canson paper on the side and gelatin filters of the same colour (or white paper) on top. 24 h lighting of 60 lux, 17 °C. After 42 days, higher weight (8.3-8.7 g versus 7.4-7.8 g) and larger size (8.9-9.1 cm versus 8.7-8.8 cm) in JUVENILES from green and yellow than from blue, red, or white aquaria 51.

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• For olfaction and risk perception ➝ D29.

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• Hearing type:
  • LAB, FRY (Rainbow and Steelhead trout hybrid): hearing GENERALIST. No accessory hearing structures enhancing detection of pressure, probably primarily sensitive to particle motion 47.
• Hearing spectrum: no data found yet.

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• LAB: ALEVINS (Rainbow and Steelhead trout hybrid) in fiberglass tanks with 1.5 m diameter, 0.8 m deep, raised under noise lower than mean sound levels recorded within commercial-scale recirculating system (115 dB re 1 microPa broadband (2 Hz to 20 kHz) root mean square; control) for 24 h/d. On day 92 (13 weeks), FRY were confronted with recorded noise higher than mean sound levels within commercial-scale recirculating system (150 dB re 1 microPa root mean square) for 24 h/d at density 10 kg/m³. Higher hearing threshold at 250 and 300 Hz at 33 and 38 weeks compared to 17 weeks indicates developmental changes in sensitivity. No difference in hearing thresholds between FRY exposed to higher than compared with lower than mean sound levels at 16 weeks, 32 weeks, and 38 weeks. Result indicates no hearing loss despite of long exposure. No difference in weight indicating no effect of noise on growth. No clear trend in glucose levels leaving doubts about stress resulting from noise. On day 195-197 (27-28 weeks), exposed to pathogen. No difference in mortalities indicates no effect on disease susceptibility 47.

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• Lateral line system and adjusting swimming movements:
  • LAB: JUVENILES (Rainbow trout) in flow tanks had lateral line (the mechanosensory hair cells of superficial and canal neuromasts) pharmacologically blocked by exposing to 0.15 mmol/L cobalt hexachloride. Blocking the lateral line decreased the ability to escape from a sudden jet of water compared to before blocking. JUVENILES displayed body wave travelling faster towards tail. No effect on tail beat frequency, maximum head angle, lateral head amplitude. Results indicate that JUVENILES use hydrodynamic feedback to adjust swimming movements. Kármán gaiting further downstream and lower body curvature only when comparing with before lateral line blocking but instead blocked vision (by turning lights off). Combining lateral line blocking and vision blocking resulted in longer and more variable wavelength, lower tail tip amplitude, lower lateral center of mass amplitude (body balance) as well as lower maximum body curvature than before all blocking 17.
  • For lateral line and vision in swimming ➝ D28.

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• LAB, JUVENILES (Rainbow trout): measuring responses to stimuli on the head, the following trigeminal receptor neuron types were identified: 17 polymodal nociceptors (heat, force, 1% acid), 22 mechanothermal nociceptors (heat, force), 18 mechanochemical receptors, 33 fast adapting mechanical receptors (fired for <0.5 s at onset of stimulus), 31 slowly adapting mechanical receptors (fired continuously during application of stimulus). No response to temperature range -7 to +4 °C 57.
• LAB: JUVENILES (Rainbow trout) in 50 x 30 x 30 cm tanks with opaque cover on one half, gravel bottom and weed and either injected with 5% or 10% acetic acid on upper and lower lips or saline (0.9% NaCl, control). Higher opercular beat rate (gill movement) in combined treatment groups compared to pre-injection at first observation time 30 min after injection (ca 90 versus 60 beats/min). Decreased over time but remained higher than pre-injection until last observation time at 180 min after injection. Lower swimming rate (ca 2-3 versus 8 swims/min) and higher use of cover (ca 50-60% versus 30%) in combined treatment groups compared to pre-injection. JUVENILES displayed anomalous behaviour like rocking from side to side on the gravel (0.6 events/min), rubbing lips in gravel or against tank walls (0.6 events/min) 26.
• For nociception and neophobia ➝ D9.

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• LAB, JUVENILES (Rainbow trout): following acid injection in upper and lower frontal lip (for details of the study ➝ D9), less frequent typical nociception-related behaviour of rocking and rubbing (0 versus 0.2-0.4 rocks/min, 0.1 versus 0.3-0.6 rubs/min) if injected with morphine sulfate at a dose of 0.3 mg/g intramuscularly (30 mg/1 mL sterile saline; 0.1 mL/10 g fish weight) afterwards 22.

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• LAB: Experiment 1: JUVENILES (Rainbow trout) were placed individually in 110 L tanks with ceramic tile on glass legs as cover and 4 cm silica sand as substrate. After introduction of 15 mL whole-body extract from skin and visceral tissue of Rainbow trouts, increase in time to capture first food item and decrease in total number of food items captured, decrease in amount of time swimming in front half of tank (near feeder) and back half (near stimulus-introduction tube) compared to control; no effect on time spent under cover. Results indicate that JUVENILES possess chemical alarm signal.
  Experiment 2: JUVENILES (Rainbow trout) were placed individually in 37 L aquaria with cover and substrate as in Experiment 1. After introduction of 10 mL skin extract of Rainbow trouts, increase in time spent under cover and decrease in time spent in open area, increase in time to capture first food item and decrease in total number of food items captured, increase in "freezing" (ceasing movement, settling on substrate, remaining motionless for 30 s) compared to control. No effect with extract from visceral tissue of Rainbow trouts and skin extract from Swordtail Xiphophorus helleri that lack known alarm pheromones except increase in amount of food items captured. Results indicate that chemical alarm signals are positioned in the skin 25.

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• WILD: ALEVINS (Steelhead trout) after emergence from the gravel congregated in schools, PARR moved solitarily downstream, defended territories, KELTS after spawning that did not immediately return to the sea were solitary or in small groups but not in schools: Waddell Creek, California, USA 6.
• WILD: stationed individually, but at last date of day-active 0+ JUVENILES (Rainbow trout) before transition to nocturnality, individuals were observed in groups of few dozens up to 200: Silver Creek, Idaho, USA 8.

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• WILD: of 0+ JUVENILES (Rainbow trout), 5.7-61.0 IND/100 m² across midchannel and stream margin and across day and night in summer, 2.0-48.0 IND/100 m² in autumn, decreasing to 0-15.8 IND/100 m² from October on until January (end of observation period): Silver Creek, Idaho, USA 8.
• Observations WILD, JUVENILES (Steelhead trout): 0.2-1.3 IND/m² given study site, at dusk in summer and autumn: Bridge river, British Columbia, Canada 7.

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• FARM: JUVENILES (Rainbow trout) raised in 2 m diameter outdoor ponds at densities 25, 75, or 125 kg/m³ for three months. Placed in 2 m diameter outdoor tanks (0.94 m³) at respective densities (28, 80, or 136 kg/m³) and proportional water renewal. After two weeks, increasingly random and disorganised swimming. Low amplitude movements during day and stationary during night at low density; circular movements during day and wide distribution during night at medium density; random and disorganised movements during day and night at high density. Decreasing turning angle with increasing density from 110° (typical for holding position) to 90° 15.
• LAB: all-female JUVENILES (Rainbow trout) in 1.82 m³ tanks (2 m diameter, 0.6 m depth) at densities of 10, 40, 80 kg/m³ (maintained until the end by removing individuals). After nine months, no difference in mortality and condition factor but in relative fin length (fin length * 100 / TOTAL LENGTH). JUVENILES in low density had longer dorsal, caudal, and pectoral fins than in medium or high density. Shorter left than right pectoral fins in medium and high density could account for swimming in the same direction as the water current. Higher cortisol in five of nine monthly samples in low than high density with first and last sample at low-stress level (2-5 ng/mL). Increase possibly due to dominance hierarchies and territoriality which got set back by removing individuals for density maintenance. Stable cortisol levels in medium and high density possibly due to adaptation to chronic stressor. Tendency of higher haematocrit in low than high density indicating either stress reponse or anaemia in medium and high density 58.

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• Inverse effect:
  • LAB: 1+ JUVENILES (Rainbow trout) in 1,500 fibreglass outdoor tanks at ca 65 kg/m³ (calculated by FEB). After three weeks, JUVENILES were removed to lower density to 25 kg/m³ (uncrowded) or added to increase density to 100 kg/m³ (crowded) respectively. Deteriorating water quality resulted in higher mortality in crowded than uncrowded JUVENILES (0.5% versus 2% per month). After sudden increase of temperature in 3 °C, overnight mortality of 13% in crowded tanks. After nine months, lower weight (ca 400 versus 500 g) and lower length (ca 30 versus 32 cm fork length) in crowded than uncrowded JUVENILES. No difference in cortisol levels (<5 ng/mL) and growth hormone (<2 ng/mL) 59.
• No effect:
  • LAB: all-female JUVENILES (Rainbow trout) in 1.82 m³ tanks (2 m diameter, 0.6 m depth) at densities of 10, 40, 80 kg/m³ (maintained until the end by removing individuals) and maintaining water parameters above critical levels. After nine months, no difference in growth but size bimodality in low density condition 58.

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• Hierarchy and group size:
  • FARM: eyed embryos (Steelhead trout) in 1,520 L circular tanks with diameter 1.8 m and enriched with tops of Douglas firs (encompassing ca 21% water volume), underwater feed delivery system, 60% overhead cover of double layer camouflage netting on PVC frame or without enrichment. After two months, FRY within 8% body weight were transported to other facility for dominance observations in 0.75 m wide x 0.75 m long sections of flume with 5 cm layer of 1-1.5 cm diameter gravel. Daphnia were constantly introduced so that individual in upstream-most position had first access. Group size started with six (three from enriched tanks, three from control tanks), dominant individual was removed, next observation, dominant removed, and so on, until only two individuals left. Among groups of six, five, four, three, or two FRY, one each became dominant. Higher dominance rank (i.e., dominant in groups with more members) in FRY from enriched tanks compared to FRY from barren tanks (12.1 versus 8.9) 14.
  • LAB: of two size-matched JUVENILES (Rainbow trout), one became dominant, the other subordinate 19.
  • LAB: in a group of 12 JUVENILES (Rainbow trout), usually one became dominant; of the subordinates, some aggressively defended territories, others floated between territories 20.
• Establishing hierarchy: within minutes to hours:
  • LAB: in 100 x 50 x 50 cm glass aquaria divided into 4 x 50 L compartments size-matched JUVENILES (Rainbow trout) were placed individually in compartments. After 5-10 days of acclimation, walls between two compartments were removed. After 0.5-90 min, fought for social dominance. After 0.5-120 min, one of JUVENILES was dominant, the other subordinate 19.
  • LAB: in a group of 12 JUVENILES (Rainbow trout), one became dominant and started defending territory within a day 20.

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• Features of dominance:
  • FARM: FRY (Steelhead trout) maintained feeding station (the most dominant FRY consistently during 20 day observations), moved freely, delivered more attacks than received, never displayed submissive behaviour, never retreated when attacked. The most dominant were the largest ones at end of study 14.
  • LAB: dominant JUVENILES (Rainbow trout) still attacked, nipped, chased subordinate when dominance fight was over and subordinate tried to be passive 19.
  • LAB: dominant JUVENILES (Rainbow trout) defended larger territories than subordinate JUVENILES (for details on the study ➝ D5) 20.
• Hierarchy and size:
  • WILD: larger SMOLTS (Steelhead trout) initiated 57% of contests, smaller SMOLTS 30%. 84% of initiators ended up dominating (for details on the study ➝ D30) 4.

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• Features of subordination:
  • LAB: subordinate JUVENILES (Rainbow trout) took position away from dominant, e.g. in a corner, and move as little as possible 19.
• Hierarchy and stress:
  • LAB: in 100 x 50 x 50 cm glass aquaria divided into 4 x 50 L compartments size-matched JUVENILES (Rainbow trout) were placed individually in compartments. After 5-10 days of acclimation, walls between two compartments were removed. After 0.5-90 min, fought for social dominance. After 0.5-120 min, one of JUVENILES was dominant, the other subordinate. At 5 min after end of fight, increased plasma cortisol in dominant and subordinate compared to control (ca 30-40 ng/mL versus ca 10 ng/mL). At 3 h after fight, still increased cortisol in subordinate (ca 30 ng/mL), back to normal in dominant. At 24 h after end of fight, further increase in cortisol in subordinate (ca 75 ng/mL) and also increase in metabolite/monoamine neurotransmitter ratios: ratio of 5-hydroxyindoleacetic acid (5-HIAA) to serotonin (5-hydroxytryptamine) compared to control and dominant in brain stem (ca 0.35 versus 0.25), hypothalamus (ca 0.15 versus 0.08), telencephalon (ca 0.45 versus 0.2-0.38), optic tectum (ca 0.6 versus 0.35), increase of ratio of 3,4-dihydroxyphenylacetic acid to dopamine in brain stem (ca 0.2 versus 0.1) and hypothalamus (ca 0.006 versus 0.0015), and increase in ratio of 3-methoxy-4-hydroxyphenylglycol to norepinephrine in brain stem (ca 0.02 versus 0.005). Results support notion of increase in serotonergic activity in subordinate usually leading to behavioural inhibition 19.

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• Size-matched pairs:
  • FARM: FRY (Steelhead trout) in sorted groups displayed aggressive attacks, lateral displays 14.
  • LAB, JUVENILES (Rainbow trout): displays, attacks, biting, circling in groups of two 19.
  • For aggression of hatchery-released SMOLTS in the wild ➝ D30.
• Non-matched pairs:
  • WILD: FRY (Steelhead trout) displayed frontal and lateral threat displays, charging, chasing, and nipping at a rate of 0-4 aggressive acts/min/IND (for details on the study ➝ D31): Eleven and Twelve Creeks, Washington, USA 1.
  • LAB, JUVENILES (Rainbow trout): chases and bites in groups of two 21.
  • LAB, JUVENILES (Rainbow trout): charges, chases, nips in groups of 12 20.

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• WILD (Steelhead trout): territory size estimated at 0.015-0.801 m² – larger than area used for foraging (for details on the study ➝ D31): Eleven and Twelve Creeks, Washington, USA 1.
• FARM: FRY (Steelhead trout) either stocked in 5 m long x 3 m wide sections of outdoor stream channel with 3-5 cm diameter gravel, two tops of Douglas fir trees, and red alder log or in equally sized section without enrichment (habitat types). 3% gradient so that water depth ranged 15-27 cm. Daphnia were constantly introduced so that individual in upstream-most position had first access. Held territories close to gravel at fastest currents, moved laterally from station to feed. In fights, FRY upstream usually defeated FRY downstream 14.
• LAB: JUVENILES (Rainbow trout) in artificial stream channel (1.9 x 0.8 m, 0.2 m deep) with gravel bed and cobbels on top at density of 0.09 kg/m² received 0.6, 1.3, 2.5, 5, 10, or 20% of wet weight dry food in constant stream at upstream end of channel. Within one day, dominant JUVENILES defended territory downstream of feeder, subordinates downstream of that, "floater" moved between territories. Larger territory in dominant than subordinate JUVENILES. Decreasing territory with increasing food abundance and increasing amount of subordinates allowed to move closer to the feeder. 15 min observation period on day 7: rate of aggression, number of aggressive JUVENILES and number of chases/IND/min displayed dome shape: increasing with increasing food abundance until 5% of wet weight dry food, then decreasing (130 aggressive acts, 60-70% aggressive JUVENILES, 0.7 chases/IND/min at 5% versus 45 acts, 40% JUVENILES, 0.2 chases/IND/min at 0.6 and 10, 20%) 20.

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• Managing self-feeder: no data found yet.
• Appearing at feeding ring:
  • LAB: JUVENILES (Rainbow trout) learned to associate a conditioned stimulus (light cue) – in place of the unconditioned stimulus of feeding – with a conditioned response (appearing at the feeding ring) 22.
• Avoidance behaviour:
  • LAB: JUVENILES (Rainbow trout) learned to associate a conditioned stimulus (light cue) – in place of the unconditioned stimulus of a plunging net into water – with a conditioned response (swimming to opposite site of shuttle box) 23.

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• LAB: JUVENILES (Rainbow trout) displayed conditioned response to conditioned stimulus without reinforcement by unconditioned stimulus (for details of the study ➝ D33) in eight out of 20 cases one day after learning trials and in seven out of 20 cases seven days after learning trials. Deterioration probably not due to fading memory but habituation 23.

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• WILD: KELTS (Steelhead trout) after spawning that did not immediately return to the sea did not resume feeding but darted at coins thrown in the water 10-12 feet away. No explanation. Authors do not assume feeding, because KELTS spit the coins out and do not assume that the coins are seen as enemies: Waddell Creek, California, USA 6. Playing?

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• Boldness and reinforcement learning:
  • LAB: individual JUVENILES (Rainbow trout) in 45 x 25 x 25 cm glass tanks with lids covered halfway to provide shelter were conditioned to appear at feeding ring in uncovered half with switching on light. Bold JUVENILES waited at ring and even jumped out of water. Most bold JUVENILES learned the feeding procedure faster than shy JUVENILES (ca 6 versus 15 trials), spent more time in uncovered half (76.3% versus 6.2%), displayed higher locomotion (1.2 times/min versus 0.4 times/min). Shy JUVENILES waited in covered half, darting out to catch food pellet and returning to shelter 24.
• Boldness and responsiveness to stressors:
  • LAB: JUVENILES (Rainbow trout) selected for high (HR) and low (LR) cortisol responsiveness to stressors in 36 L aquaria (40 x 30 x 30 cm) covered with black plastic sheets on three sides. Baseline feeding for six days, challenge testing for three days: a) novel object test, b) resident-intruder test, c) confinement test, repeated once to result in 18 days.
    a) On day 7, novel object test: ➝ D9.
    b) On day 8, resident-intruder test: intruder of 30-50% body mass introduced to aquarium. No difference in latency to attack (medians: LR = 315 s, HR = 205 s) and total number of aggressive acts towards intruder (medians: LR = 14, HR = 21). Repeated on day 17, no difference in latency to attack (medians: LR = 285 s, HR = 183 s) and total number of aggressive acts towards intruder (medians: LR = 21, HR = 14), but positive correlation in latency to attack between first and second round.
    c) On day 9, confinement stressor test: JUVENILES transferred to 5 L confinement boxes covered with grey walls on three sides. After 30 min, no difference in locomotor activity (medians: LR = 63 s, HR = 37 s). Repeated on day 18, no difference in locomotor activity (medians: LR = 46 s, HR = 53 s), but positive correlation between first and second round 21.
• For differences in stress responses to acute stressors ➝ D34.

^{In the structure of menu item 16 and the definition of "SHYNESS-BOLDNESS", we follow 60.}

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• Novel object test:
  • LAB: JUVENILES (Rainbow trout) in individual 45 x 25 x 35 cm tanks, 50% covered by opaque polyethylene attached to the lit as cover for sheltering. Under anaesthesia, injected with sterile saline.
    Experiment 1 group: after 5 min, novel object slowly lowered into tank ca 10 cm from head of JUVENILES, removed after 15 min. Repeated four times at hourly intervals with different object each time.
    Experiment 2 group: made familiar with object by placing it in tank for 8 h/d on four days. After presentation of novel object: longer latency to approach (6.8 versus 1.6 s), shorter amount of time spent in proximity (2.2 versus 27.8%), larger amount spent away from object (76.9 versus 22.2%) compared to a familiar object indicating neophobia (for more details on study ➝ Neophobia and nociception below) 22.
  • LAB: JUVENILES (Rainbow trout) selected for high (HR) and low (LR) cortisol responsiveness to stressors in 36 L aquaria (40 x 30 x 30 cm) covered with black plastic sheets on three sides. Baseline feeding for six days, challenge testing for three days: a) novel object test, b) resident-intruder test, c) confinement test, repeated once to result in 18 days.
    a) On day 7, novel object test: yellow rubber stopper dropped in aquarium. No difference in locomotor activity (medians: LR = 41 s, HR = 74 s), frequency of entering the zone containing the object (medians: LR = 11, HR = 13 times), time spent in zone (medians: LR = 110 s, HR = 126 s) but decrease in LR in mean feed intake to 33% of baseline feeding. Repeated on day 16 (after another six days after third test), no differences: locomotor activity (medians: LR = 20 s, HR = 36 s), frequency of entering the zone containing the object (medians: LR = 8, HR = 11 times), time spent in zone (medians: LR = 332 s, HR = 70 s) but decrease in LR in mean feed intake to 11% of baseline feeding. The latter differs from results in other studies and indicates context dependency and behavioural flexibility and possibly that stress reactivity and coping may be uncoupled.
    b) On day 8, resident-intruder test: ➝ D8.
    c) On day 9, confinement stressor test: ➝ D8 21.
• Neophobia and nociception: pain decreases neophobia, stress from novel objects induces hypoalgesia:
  • LAB: JUVENILES (Rainbow trout) in individual 45 x 25 x 35 cm tanks, 50% covered by opaque polyethylene attached to the lid as cover for sheltering. Under anaesthesia, injected with 0.1 mL 2% acetic acid in upper and lower frontal lip (sterile saline in control group). Typical nociception-related behaviour: rocking from side to side on substrate on either pectoral fin, rubbing lips into substrate or against tank walls. After 5 min, novel object slowly lowered into tank ca 10 cm from head of JUVENILES, removed after 15 min. Repeated four times at hourly intervals with different object each time. Shorter latency to approach novel object (3.2 versus 6.8 s), larger amount of time spent in proximity of novel object (31.8% versus 2.2%), and smaller amount spent away from the object (19.6% versus 76.9%) in acid compared to control group. Less frequent rocking and rubbing before and after presentation of object compared to group that was made familiar with object (0.2 rocks/min and 0.3 rubs/min versus 0.4 rocks/min and 0.6 rubs/min). Results indicate that acid group's attention was probably mostly directed towards nociception which resulted in reduction of neophobia. Additionally, stress linked to novel object seemed to induce hypoalgesia with individuals dividing attention between nociception and fear 22.

^{In the structure of menu item 16 and the definition of "EXPLORATION-AVOIDANCE", we follow 60.}

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• For aggressiveness and...
  ...establishing hierarchy ➝ D2,
  ...dominance ➝ D7,
  ...subordination ➝ D35,
  ...size-grading ➝ D36.

^{In the structure of menu item 16 and the definition of "AGGRESSIVENESS", we follow 60.}

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• LAB: individual JUVENILES (Rainbow trout) in shuttle box of 80 x 190 x 37 cm (water depth 27 cm) with two compartments separated by opaque divider with 18 x 21 cm opening. When dip net was suddenly plunged into water, majority of JUVENILES learned that they could avoid frightening stimulus by swimming into opposite compartment. Held also when light was presented instead of frightening stimulus (➝ D33 D37), although longer latency to initiate flight (6.6 versus 3.2 s). Result indicates that avoidance behaviour is conscious decision – instead of automatic response – probably motivated by fear. Five of 18 JUVENILES that failed to react sank to bottom, freezing. Were probably so frightened that were unable to react and discarded from analysis 23.
• For fear after stress signals by conspecifics ➝ D29.

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• Anaesthesia and injection:
  • LAB, JUVENILES (Rainbow trout): higher opercular beat rate (gill movement) after anaesthesia and injection of either acid or saline compared to baseline indicating stress by handling; higher increase for acid (median 80 versus 55.2 beats/min) compared to saline group (median 67.2 versus 52.6 beats/min) (for more details on study ➝ D9) 22.
• Confinement, transport, chasing, netting:
  • LAB: JUVENILES (Rainbow trout) were confined to small area of pond, netted, transported in 10 L bucket for 10 min to tank, chased and netted. Higher serum cortisol (5.5 µg/dL versus 1.5 µg/dL, ranges 3.0-12.3 µg/dL versus 0.1-3.0 µg/dL), higher serum glucose (ca 60 mg/dL versus ca 28 mg/dL, ranges 40-91 mg/dL versus 10-39 mg/dL), and higher lysozyme activity (ca 550 units/mL versus 320 units/mL, ranges 320-980 units/mL versus 140-480 units/mL) in stressed than unstressed JUVENILES 49.

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• LAB: 1+ JUVENILES (Rainbow trout) in 1,500 fibreglass outdoor tanks at ca 6.4 kg/m³ (calculated by FEB). Transferred to 80 x 40 x 20 cm tanks (ca 148.8 kg/m³, calculated by FEB). After 30 min confinement, higher plasma cortisol levels than control (80 ng/mL versus <2 ng/mL). After 1 h confinement returned to rearing tanks. Cortisol levels decreased but remained elevated until at least 4 h later. At next measuring point 8 h after stress, back to basal levels. Lower growth hormone levels in stressed JUVENILES compared to control (0.7 versus 1.3 ng/mL) 59.
• LAB: female 1+ JUVENILES (Rainbow trout) in 1,500 fibreglass outdoor tanks at ca 12.6 kg/m³ (calculated by FEB). Sample transferred to 80 x 40 x 20 cm tanks (ca 44.3 kg/m³, calculated by FEB) for 0, 1, 4, 8, 12, or 24 h. Higher plasma ACTH (ca 50-85 pg/mL versus 15-20 pg/mL), higher plasma cortisol (ca 50-73.2 ng/mL versus 2 ng/mL), and lower growth hormone in stressed JUVENILES than control at all times 59.
• LAB: JUVENILES (Rainbow trout) in 83 x 49 cm and 42 cm deep glass tanks at density 8.6 kg/m³ and either white, red (605 nm), or blue light (480 nm) at 150 lux. After 111 days and additional 48 h fasting period, confined for 1 h by lowering water to 10 cm water level (35.7 kg/m³ density). Increase in cortisol levels compared to control group (35.2-36.8 versus 2.1-3.2 ng/mL), less pronounced under blue light (26.6 ng/mL). Increase in plasma glucose (100.1-103 versus 73.1-82.3 mg/100 mL), less pronounced under white light (92.2 mg/100 mL) 43.
• LAB: JUVENILES (Rainbow trout) selected for high (HR) and low (LR) cortisol responsiveness to stressors transferred to 5 L confinement boxes covered with grey walls on three sides. After 30 min, higher plasma cortisol in HR than LR individuals (ca 70 ng/mL versus 20 ng/mL) 21.

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• FARM: female JUVENILES (Rainbow trout) were transported for 5 h in rearing water or rearing water supplemented with 5 g NaCl/L. Higher blood glucose in JUVENILES of normal water compared to supplemented water and control (ca 125 mg/dL versus 50-75 mg/dL). Higher cortisol levels in both transport groups compared to control (ca 50-90 ng/mL versus 10 ng/mL). Higher increase in skin-associated bacteria in JUVENILES of normal water compared to control (ca 50-fold increase); supplemented water in between (ca 10-fold increase). Skin of JUVENILES in normal water covered in thick mucus nets unlike control; JUVENILES in supplemented water with thin mucus layer. Higher number (ca twofold) of goblet cells containing mucins in both transport groups compared to control. Higher number of sulfated goblet cells in JUVENILES of normal compared to supplemented water. Lower killing activity against bacterial pathogen V. anguillarum in JUVENILES of normal water and control compared to JUVENILES of supplemented water (20% versus 11-12%) 61.

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• WILD: hatchery-reared and wild-caught Rainbow and Steelhead trout JUVENILES confined in 91 x 99 cm, 91 cm deep enclosures with plywood top in stream for 42 d (for details of experiment ➝ D30). No difference in condition factor compared to individuals caught outside enclosures (1.18-1.20), lower cortisol levels in enclosed JUVENILES. Possibly due to overhead cover and protection from predation: Teanaway river, Washington, USA 3. oder soll ich einen extra unterpunkt "confinement" einführen wie bei acute stress?

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• Stunning rules: to minimise pain reactions and enhance welfare before slaughter:
  1. induce insensibility as fast as possible,
  2. prevent recovery from stunning,
  3. monitor effectiveness (observations, neurophysiological measurements) 62.

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• Electrical stunning:
  • FARM: authors tested a rotary stunning unit consisting of a tank with 12 slowly rotating channels (each 0.2 m wide, 1 m long, 0.2 m deep) into which individuals are pumped. Channel walls are electrodes between which an electric field of strength 250 V/m r.m.s. is built using a sinusoidal 1,000 Hz waveform. Individuals are immediately stunned when entering the channels, rotating at <1 rpm for 60 s. The duration or the field strength should be adapted to the water conductivity at the site. Stunned individuals are washed out into collecting tank. Testing on four farms yielded processing speed of 2 t/h. Higher speed bears risk of individuals remaining in channels and being stunned again. Reduces processing capacity and might result in backlog in delivery pipe. Low power requirement due to low water volume used, compact enough to be transported. Similar levels of haemorrhages but decreased slime and blood on carcasses and increased latency to go into rigor compared to traditional stunning techniques 63.
  • LAB: Experiment 1 (duration): JUVENILES (Rainbow trout) in water bath with two 50 cm long electrode plates 56 cm apart at 13 cm water depth were stunned with 128 V r.m.s (root mean square) at 50 Hz sinusoidal a.c. for 1, 5, 10, 20, or 30 s. Increasing mortality with increasing duration, with 10 of 10 deaths at 30 s, and increasing time to recovery of opercular movement.
    Experiment 2 (frequency): JUVENILES in water bath with two 50 cm long electrode plates 13 cm apart at 10 cm water depth were stunned at 50, 100, 300, 500, 750, 1,000, or 2,000 Hz sinusoidal a.c. for 5 s. No mortality. Stun duration at least 20 s but lower at 2,000 Hz (min 10 s). Decreasing time to recovery with increasing Hz, with 0 s between 2,600 and 2,800 Hz.
    Experiment 3 (magnitude): JUVENILES taken out of the water, fixed into wooden clamp. Electrodes in soaked sponges directly applied to the head, stunned with 25, 30, 40, 45, 50, 60, 70, 90, 110, or 120 V r.m.s. for 1 s, returned to water. Increasing time to recovery and increasing mortality with increasing current.
    All experiments: tonic phase when current was applied where body is rigid, mouth open, fins stretched. Slight relaxation when current was turned off. Twitching along the body, rolling upside down. No swimming or breathing. If recovered, opercular movement started, individual regained equilibrium. Sporadic muscle spasms until 5 min after end of stunning.
    Results indicate for stunning outside water with electrodes to head minimum current: 100 mA at 50 Hz for 1 s. Inside water with electrode plates, minimum current: 8.3 A/m² at 50 Hz for 5 s to stun or 30 s to kill. At 10.2-10.8 A/m² and 5 s, maximum frequency: 2,000 Hz 64.

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• FARM: ADULTS (Rainbow trout) in 3,600 L tanks treated either with
  a) electroshock for 30 s at 180 V and 50-60 Hz with electronic teaser, then percussively slaughtered,
  b) asphyxia in air at 15 °C (15 min), then percussively slaughtered,
  c) asphyxia with carbon monoxide until death (49 min).
  Lower plasma glucose levels in electrically stunned ADULTS compared to asphyxia with carbon monoxide (5.0 mM versus 7.9 mM); air asphyxia in between (6.1 mM). Lower plasma lactate levels (3.5 mM versus 5.9-6.3 mM) and lower osmolality (325.9 mOsm/kg versus 340.0-340.9 mOsm/kg) in electrically stunned ADULTS compared to both asphyxia methods. No difference in cortisol levels due to large individual differences. No difference in onset, strength, and duration of rigor mortis. Lower muscle ph in ADULTS asphxiated in air until 48 h post mortem; no difference at rigor resolution at 76 h post mortem 65.
• LAB: JUVENILES (Rainbow trout) in 50 x 34 x 19 cm polythene tank in either 20 °C or 14 °C or chilled to 2 °C and exposed to MS 222 to implant electrodes. No visual evoked responses to light flashes during anaesthesia. JUVENILES in 2 °C took longer to regain consciousness than JUVENILES in other conditions. No difference in visual evoked responses during consciousness: 200-300 microV, similar amplitude. Higher latency in 2 °C (55 ms) than 14 °C (20 ms) and 20 °C (15 ms). After recording, removed from water to either room temperature (20 °C or 14 °C) or crushed ice (2 °C). Longer time to loss of visual evoked responses in 2 °C than in 14 °C or 20 °C (578 s versus 158-180 s). More vigorous escape attempts under 20 °C and 14 °C than under 2 °C. Longer time to loss of visual evoked responses when JUVENILES hardly moved indicating faster anoxia with greater metabolic activity. After loss of visual evoked responses still respiratory and sometimes also muscular activity. Longer time to loss of all physical movement in 2 °C (197 min) than 14 °C (27.7 min) or 20 °C (11.2 min) 50.

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