Reviewer: Kerstin Glaus
Editor: Billo Heinzpeter Studer

Initial release: 2014-03-15
Version information:

• Appearance: B
• Last minor update: 2022-01-22

Cite as: »Volstorf, Jenny. 2022. Salmo salar (Dossier). In: fair-fish database, ed. fair-fish. World Wide Web electronic publication. Version B | 1.1. https://fair-fish-database.net.«

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• Unpredictable influence:
  • Observations WILD: non-mature JUVENILES entered fresh water 1.
• Competition:
  • Observations WILD: additional competitor for food 2.
• Disease transmission:
  • Observations WILD: possible transmitter of diseases and parasites 2.
• Interbreeding:
  • Observations WILD: breeding with native populations could reduce fitness and productivity in hybrids (because of the smaller genetic variability in farmed individuals) and eventually survival 3.

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• No general preferences for substrate, water velocity, depth, and water temperature. This may be due to several factors:
  • Genetic adaptation to local habitats, e.g., larger pectoral fin in fast-flowing streams 4.
  • Species is tolerant of wide range of conditions 4.
  • Between-study variation, e.g., individuals may use preferred habitat at low densities but sub-optimal habitat with increasing density 4. There is a difference between habitat use and preference: Preference can only be determined at a wide range of habitat availability, i.e. when individuals may choose the preferred condition, not when they simply adjust to what is available 5↶6 . Many studies reporting depth preference are biased in that they only observed shallow sections of rivers, but hydrostatic pressure is not high or light intensity not low enough to prevent PARR from diving in deeper parts of rivers 7.
  • Variables interact 4.
• Habitat preference: not only determined by substrate but a complex interaction between hydro-geomorphologic, ecologic, and dynamic factors 8 9 10.

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• For feeding ➝ 6 11.
• For daily rhythm ➝ 12.
• For swimming ➝ 6.
• For migration ➝ 13.
• For nest building ➝ 14.
• For territoriality ➝ 15 11.

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• For swimming ➝ 16 17 18.
• For schooling ➝ 19.
• For dominance and subordination ➝ 20 21.
• For aggression ➝ 22 23 24 25.
• For learning ➝ 26.
• For coping styles ➝ 27 20.

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• Observations: northern Atlantic coasts of Canada and the USA, southern Greenland, Iceland, and United Kingdom, as well as Scandinavia to Portugal 29↶30 31↶32 33.
• Observations Canada: Catamaran brook, New Brunswick, Canada 34 35 11, Escoumins river, Québec, Canada 8, Magaguadavic river, New Brunswick, Canada 1, Petite Cascapédia and Bonaventure river, Québec, Canada 10, Sainte-Marguerite river, Québec, Canada 9 8, West Salmon river, Canada 12.
• Observations United Kingdom: river Bush, Northern Ireland 36, Girnock Burn, Scotland 37, Newmills Burn, Scotland 38, several rivers in England and Wales 14.
• Observations Scandinavia, Russia: Eidfjord, Norway 39, river Lilleaa, Denmark 13, Louvenga river, Russia 15, river Tana, Finland 40, river Teno and tributaries, Finland 41, river Tverrelva, Norway 42, rivers Todalselva, Vindøla, and Humla, Norway 7.

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• Observations Bering Sea: 2.

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• Plants: no data found yet.
• Rocks and stones:
  • Observations WILD, FRY: 16-256 mm 43↶4.
  • Observations WILD, PARR: 64-512+ mm 43↶4 44↶4 45↶4, 20-1,000 mm: river Teno and tributaries, Finland 41, 30-60 mm: Sainte-Marguerite river, Québec, Canada 9, 80-500 mm: river Tana, Finland 40, 0-2 years: gravel > cobble > sand 46, ≥256 mm: Petite Cascapédia and Bonaventure river, Québec, Canada 10, 16-250 mm: Catamaran brook, New Brunswick, Canada 34, 200-400+ mm: Catamaran brook, New Brunswick, Canada 35, 4-256+ mm 47, 30-60 mm: Louvenga river, Russia 15.
  • Substrate serves as holding station while feeding 48↶10 49↶10 50↶10.
  • For substrate and nest building ➝ D1.
• Sand and mud: avoids mud and fine substrate:
  • WILD, ALEVINS: infiltration of sediment may negatively affect embryo survival, because the fine materials limit water flow through the substrate resulting in lack of oxygenation 51↶37 36 and poor removal of metabolic waste 14 51↶37 52↶4. ​
  • WILD: PARR avoided fine substrate (<10 mm) 6.
  • WILD/LAB: in flow-through tank with river water, decreasing survival of ALEVINS with increasing percentage of fine material <1mm: adding 10% fines decreased survival from 38% to 9.3%; at 25% fines, 0% survival. In river without tank (river Bush, Northern Ireland), no correlation between percentage fine material and embryo survival. Time of oxygen stress through infiltration seems essential: embryos in tank were subjected to fines in earliest developmental stages, embryos in river experienced fines as those accumulated over time 36.
  • WILD: decreasing survival of embryos with increasing percentage of fines <1 mm (Sainte-Marguerite river, Canada): coarse sand (<1 mm) and smaller material negatively correlated with survival of hatched embryos, fine sand (<0.3 mm) and smaller material with survival of pre-eyed and eyed stages – although fines (<1 mm) only amounted to 3.3-29.2% of all material, fine sand (<0.3mm) only to 0.4-6.4% 53.
• Other substrate: no data found yet.

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• LAB: ALEVINS (until exogenous feeding) grew better when reared on artificial substrate (polyethylene astro-turf) than on flat screen, because no vertical stability without substrate results in swimming and decreased conversion from yolk to body weight. FRY showed best yolk conversion efficiency when transferred to feeding tanks (without substrate and with increase in temperature from average 9.6 to average 12.5 °C) on day 28 than on day 19, 22, or 43; best weight when transferred on day 22 and 28 than 19 or 43 54.

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• Plants:
  • WILD: decreasing PARR density with increasing vegetation (rooted aquatic macrophytes), probably because it limits visibility and thereby feeding opportunities. Of 94% taking cover, most (53%) used a cobble-sized or larger stone, 37% used rooted aquatic macrophytes, 10% used woody debris or overhanging riparian vegetation. Moderate vegetation might provide alternative cover in gravel and sand areas that lack coarse-substrate cover 46.
• Rocks and stones:
  • WILD: ALEVINS remain covered by gravel for 2-15 weeks depending on temperature and how long their yolk sacs last 16.
  • WILD: JUVENILES preferred complete cover, avoided areas with partial cover 34.
  • WILD: PARR preferred larger substrate during the day than at night, probably because they use the interstitial pockets as cover from predators as well as shelter from high velocities 55.
  • JUVENILES-ADULTS use substrate as cover from predators 49↶47 56↶47 57↶9 58↶10 46.
• Sand and mud: no data found yet.
• Other cover:
  • WILD: abandoned spawning channel at Noel Paul's Brook, Canada, with three types of sections: a) control, including gravel substrate and 13-60 cm boulders along the banks, b) mid-channel, including a low-head barrier dam and a cluster of five large boulders (30-60 cm diameter), c) stream bank, including two artificial undercut banks, two wing deflectors, optional overhanging cover. When given the choice, PARR preferred the stream bank section over the mid-channel section (probably due to too little discharge in the latter), control section in between. At higher density (99 versus 68 PARR/100 m²), PARR were indifferent between the sections. In the mid-channel section, PARR took a position closer to cover than in the other sections. In the stream bank section, PARR moved deeper (18-21 cm versus 15-18 cm in mid-channel versus 10-15 cm in control section) than in other sections 55.
• Low temperatures and shelter: seeks shelter from cold temperatures by building pools 59↶60 or hiding in interstitial pockets:
  • Observations hiding: eggs and JUVENILES 61↶47 49↶47 56↶47 62↶63, LAB, PARR 64.
  • WILD: PARR preferred larger substrate during the day than at night, probably because they use the interstitial pockets as shelter from low temperatures 55.
  • WILD: PARR tended to avoid finer substrate with decreasing temperatures 6, probably because only coarser work as shelter 43↶6.
  • LAB: at low temperatures (3.4 °C), PARR sought shelter made from 1 L opaque plastic bottles cut in half lengthways creating cavities 17 x 9 x 4 cm deep, with a 2.5 x 3.0 cm wide opening on level with the gravel surface. Average of one PARR per shelter, therefore – at a constant number of shelters – the larger the population the less PARR sheltered 18.
  • LAB: the more PARR sought shelter the less PARR lost weight, probably because they saved metabolic costs otherwise spent on predator alertness or competition for shelters 64.
• High temperatures and shelter: seeks shelter at high temperatures:
  • Observations WILD: 14-23 °C: 45% of FRY, 10% of PARR 65↶4, 66↶60.
  • Without shelter, temperatures of >24 °C might be fatal for PARR 67↶60.

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• FARM: covering 67% of tank surface with floating cover (fibreglass and polystyrene, attached to the side of the tank with nylon guy-lines) increased the proportion of FRY to SMOLTS congregating beneath the cover versus over the aluminium grill on the tank ground, increased the growth rate, had little effect on the severity or duration of ectoparasitic infestations, had no effect on mortality. Control group without cover displayed decreased thrombocyte and lymphocyte count indicating stress. Disadvantage of having to take cover off for cleaning outweighed by reduced algal growth on tanks due to light limitation 68.

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• Observations: 4.5±0.3 se 63.

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• Carnivorous D2. 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 69 or even 1/3 70 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 71, the individual fish gets overlooked and, thus, suffering increases at rearing, live marketing, and slaughtering levels 72.

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• Food items: carnivorous:
  • Observations WILD, PARR (1-3+ years): invertebrates: mainly aquatic insects: mayfly nymphs, caddis larvae, and flying insects: river Tana, Finland 40, Louvenga river, Russia 15, stonefly nymphs, simuliid larvae and pupae: river Tana, Finland 40.
• Food items and habitat: no data found yet.
• Food items and life stages: generally high overlap in food items but some difference between life stages:
  • Observations diet overlap WILD: great diet overlap between 2- and 3-year-old PARR, larger difference to 1-year-old PARR 40.
  • Observations prey size WILD, PARR: for prey present in all age groups, 1-year-old fed on smaller, 2- and 3-year-old on larger species 40.
  • Observations habitat WILD, PARR: 1-year-old mainly Mayfly nymphs and simuliid larvae and pupae from the benthos, 2- and 3-year-old mainly large Trichoptera larvae and flying insects from the drift 40.
• 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: PARR fed on benthic as well as drift prey 40.
• WILD, PARR: multiple central-place forager (for details ➝ D3): sit-and-wait, switch foraging stations, rarely attack while moving. Young-of-the-year PARR mostly foraged on drift prey than benthos (75-99.1% versus 0-25%); no correlation with current velocity. Larger PARR attacked prey from greater distance: Catamaran Brook, New Brunswick, Canada 11.
• For foraging and vision ➝ D4.

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• LAB: In groups of ten 1+ year old PARR, no difference in growth but more - and more severe - dorsal fin erosion under unpredicted than predicted feeding schedule, indicating stress. More aggression and more attacks in groups with predicted than unpredicted feeding schedules might represent food-anticipatory behaviour 21.

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• LAB: JUVENILES with low feed intake and low growth rate in group rearing had higher feed intake and higher growth rate when reared in isolation for four weeks, probably because of missing competition 27.

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• Feeding and temperature: either ceases feeding with low temperatures, still feeds but decreasingly so, or turns to nocturnal feeding:
  • Observations cessation: 6-7 °C 75↶76 56↶76.
  • Observations decrease WILD, PARR: 4.9-16 °C 6, 1-6 °C 77↶78.
  • Observations nocturnal WILD, PARR: -0.5-0.2 °C 6; LAB, JUVENILES: <10 °C 79↶6.

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• Daily rhythm:
  • LAB: JUVENILES are diurnal 80↶81 81 and possibly used to sleep during night 81.
  • LAB, PARR: visual forager and territory defender (less active and territorial in dark conditions). Aggressive interactions increased with increasing light intensity: up to average of five times more aggressiveness at intensity of one hour before sunset (1 lux) versus complete darkness. Tolerated distance to nearest neighbour increased with increasing light intensity, but most likely does not have to do with conspecifics but with reduced visibility of feed that determine the size of the territory to defend – might still be territorial but defend much smaller territory. Also explains findings of higher locomotion in dusk and dawn: PARR re-establish/adjust territories 22.
• Nocturnal activity and low temperatures: switches to nocturnal behaviour when temperatures fall:
  • Observations WILD, JUVENILES: <8 °C 56↶10, 0-3.1 °C 12.
  • Observations WILD, PARR: 79↶4 82↶4, 4-18.5 °C 55, 0-3 °C 35, -0.5-0.2 °C 6.
  • WILD: in winter (0-3.1 °C), 18 of 19 JUVENILES active throughout diel cycle, one nocturnal. JUVENILES less active during daytime than nighttime with peaks at 1 a.m. in early and ca 10 p.m. in late winter 12.
  • WILD: SMOLTS migrated predominantly nocturnally at temperatures of 5-10 °C 13.
• Nocturnal activity and predator avoidance:
  • SMOLTS migrate at night, probably to avoid avian and fish predators 83↶13 84↶39.
• Phototaxis: photonegative:
  • LAB: newly hatched ALEVINS (0-20 days) accumulated in the aquarium corners most distant from the light source 16, probably to make sure ALEVINS in streams settled in the protection of the gravel 85↶16. With exhaustion of the yolk sac, individuals lost the photonegative behaviour 85↶16.
• For daily rhythm and depth ➝ D8.

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• Standard temperature range: -0.5-23 °C:
  • Observations WILD: 0-19 °C: river Teno and tributaries, Finland 41, 1.8-6.7 °C: river Bush, Northern Ireland 36, 8-20 °C: rivers Todalselva, Vindøla, and Humla, Norway 7, -0.5-17.7 °C: rivers Todalselva and Vindøla, Norway 6, 0.2-17 °C: river Tana, Finland 40, 2-15 °C: river Lilleaa, Denmark 13, 0-3.1 °C: West Salmon river, Canada 12, 14-23 °C: rivers Escoumins and Sainte-Marguerite, Canada 8, 21.5-23 °C: Catamaran brook, Canada 34, 0-3 °C: Catamaran brook, Canada 35, 7-12 °C: Eidfjord, Norway 39, 17.5-22.5 °C: Catamaran brook, New Brunswick, Canada 11.
  • WILD: ADULTS spawn in rivers where the temperature rises above 10 °C for about three months per year and does not exceed 20 °C for more than a few weeks in summer 62↶63.
• Temperature preference: 4-17.5 °C:
  • Observations: 4-12 °C 62↶63, 12-15 °C 86↶87, 16-17.5 °C 88↶87.
• Migration temperature:
  • WILD: SMOLTS migrate to the sea at a temperature range of >5-10 °C 89↶47.
• For temperature and...
  ...shelter ➝ D9,
  ...daily rhythm ➝ D4,
  ...swimming ➝ D10,
  ...column velocity ➝ D11,
  ...depth ➝ D8.

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• Lower and upper lethal limits:
  • Depend on acclimation 90↶4.
  • Lower lethal limit:
    a) incipient (survival over 7 days): 0-2 °C (eggs: 0 °C, ALEVINS: 0-2 °C, PARR: 0-2 °C) 78,
    b) ultimate (survival for no more than 10 min): -0.8-1 °C (PARR: 0-1 °C, -0.8 °C) 78.
  • Upper lethal limit:
    a) incipient (survival over 7 days): 16-28 °C (eggs: 16 °C, ALEVINS: 23-24 °C, PARR: 22-28 °C) 78,
    b) ultimate (survival for no more than 10 min): 24-33 °C (ALEVINS: 24-25 °C, PARR: 30-33 °C) 78.
• Ice cover:
  • WILD: dominant problem is the low flow that decreases the overwintering habitat area: redds may freeze 91↶92 93↶92, FRY may strand and suffocate, freeze, or fall prey to predators 94↶30. Ice cover reduces the spawning season to between breakup of the old and formation of the new cover which potentially minimises future populations 30.
• Egg-to-SMOLTS survival in rivers with potential ice cover: 0.4-6.2%:
  • Observations WILD: 0.6-6.2% 95↶92, 1.7%: Newfoundland rivers 91↶92, 0.4%: two Irish rivers 96↶92, 0.3-1%: Newfoundland rivers 97↶92, 0.4%: Catamaran Brook, New Brunswick, Canada 92.

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• Temperature must exceed: 1-7.7 °C:
  • Observations WILD: 1-6 °C 77↶78, 5.6 °C 98↶76, 6 °C 99↶76, 6.3-7.4 °C 100↶76 101↶76, 7 °C 95↶76 102↶76, PARR: 6-7 °C 75↶76, 7 °C 103↶76.
  • Observations LAB: <1 °C 104↶76, 6-7 °C 56↶76, 1-7.7 °C 78, PARR: 6 °C 76.
• Temperature must not go beyond: 22.5-26.7 °C:
  • Observations: 23 °C 76, 22.5-26.7 °C 78.
• Optimal temperature for growth: 14-19 °C:
  • Decreasing with decreasing energy 78.
  • Observations: 14-18 °C 86↶87, PARR: 16-19 °C 48↶76 105↶76 106↶76, PARR feeding to satiation: 15.9 °C 76.
• For temperature and feeding ➝ D12.

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• Obsevations: high egg survival rate at ≥7 mg/L oxygen concentrations and 12.5 °C incubation temperature (lower oxygen concentrations tolerated at lower temperatures) and ≥100 cm/h water velocity 90↶4.

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• Salinity tolerance:
  • Natural and introduced distribution in fresh water from egg to PARR stage and again as GRILSE, in between as SMOLTS in seawater D13 D14 D15.
• Standard salinity range: no data found yet.

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• Standard pH range:
  • Observations WILD, PARR: pH 6.8-7.9: river Teno and tributaries, Finland 41.
• pH preference: no data found yet.

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• Lower and upper lethal limits:
  • FARM, JUVENILES: tolerance towards pH levels differed during life stages. No effect at pH ≥5.4, but increasing mortality with decreasing levels 47.

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• Swimming type: sub-carangiform:
  • Observations: 107↶108 109.
• Ontogenesis of swimming behaviour:
  • FARM, ALEVINS (0-40 days), in glass aquaria without substrate:
    a) day 0-10: most ALEVINS have an on-side, on-bottom, or upright orientation. If in upright orientation, the ventral surface of the yolk sac is in contact with the substrate, the anterior-posterior axis is at an angle of 45 degrees off horizontal with the head pointing down. ALEVINS move their tails or entire bodies resulting in changes between the different orientations or forward motion in the head-down position. By flexing the posterior portion of the body and pushing off the substrate with the lateral body wall, ALEVINS display sudden vertical movements followed by a passive dropping to the substrate 16.
    b) from day 10 on: the anterior-posterior axis in upright position is horizontal. If moving, ALEVINS may now additionally swim freely and reach the water surface 16.
    c) from day 20 on: the predominant orientation is still on bottom and upright. The pectoral fin tips and the ventral portion of the caudal fin come in contact with the substrate with the anterior-posterior axis at an angle of approximately 10 degrees off horizontal with the head pointing up. Movements to change between different orientations without leaving the substrate decrease by day 30 16.
    d) from day 30 on: The orientation is off bottom, and free swimming prevails 16.
• Buoyancy:
  • ADULTS inflate swim bladder and maintain buoyancy by swallowing air 110↶111 during jumping behaviour 112↶111.
  • FARM: after diving away from a light source (➝ D8), ADULTS deflated the swim bladder, leading to a 29% reduction in echo-signal, and increased swim bladder re-filling afterwards 113.This supports the hypothesis that salmons release gas from the swim bladder to facilitate escape 110↶113.
• Passive swimming:
  • WILD: when SMOLTS have chosen their position in a river, transportation downstream is almost passive 114↶60.
  • WILD: because post-SMOLTS migration patterns have been found to be correlated with water currents 115↶60 116↶60, transportation seems to be passive.
• Swimming direction:
  • WILD: usually, downstream-migrating SMOLTS swim head first, only temporarily going upstream at too steep velocity gradients 117↶60. They continue downstream movement if there is no other way of escape 118↶60.
• Station holding:
  • LAB, PARR: station holding at a speed <10 cm/s by “standing on the tips of their extended pectoral fins and heading upstream with the body at an angle of 10-15° to the substratum” 17. From speed of 50 cm/s on, body parallel to the bottom, dorsal fin progressively furled. Passive behaviour to 1) avoid swimming but stay close to fast currents whose speed they could not endure very long, 2) look for food and be ready to catch it 17.

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• Absolute swimming speed: 0.2-28 km/d in streams or fjords, 15-30 km/d at sea:
  • Observations in streams or fjords WILD: SMOLTS: 0.2-28 km/d in 119↶13, 1-7 km/d 13, KELTS: 10 km/d 120↶60.
  • Observations at sea WILD: post-SMOLTS 121↶60 and KELTS 120↶60 122↶60 ca 15-30 km/d.
• Relative swimming speed: no data found yet.
• (Swimming) activity and temperature: decreases activity with decreasing temperatures:
  • WILD: at <5 °C, most FRY hid in the substratum; at 6-7 °C, FRY came out of hiding, but remained relatively inactive on the streambed; at 10-11 °C, FRY became more active in faster open water 75↶4.
  • WILD: JUVENILES less able to hold position on substratum during winter than during summer 123↶4. Swimming ability impaired with decreasing temperatures 124↶6 125↶6 126↶6.
  • WILD, PARR: decreasing station holding with decreasing water temperature 6. The larger the individual, the fewer movements 12.
  • LAB: PARR rested on substratum rather than swam in the current 18.
  • Optimal temperatures for swimming: 16-17 °C 127↶60.

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• Snout water velocity as experienced by individuals: 4-50 cm/s:
  • Observations WILD, FRY: 10-30 cm/s 49↶4, 5-15 cm/s 50↶4.
  • Observations WILD, PARR: 10-50 cm/s 49↶4, 5-35 cm/s 50↶4, 0-20 cm/s 45↶4, 4-50 cm/s 6.
  • WILD: habitat preference of JUVENILES best predicted by mean flow velocity, probably because correlated with drift rate: JUVENILES avoided flows <3 cm/s, preferred flows >6 cm/s, range over the summer: 6-48 cm/s, highest preference: >30 cm/s at water depth of 30 cm 34.
• Column velocity: 5-120 cm/s:
  • Observations WILD, FRY: 10-30 cm/s 128↶4, <100 cm/s 44↶4, 20-40 cm/s 129↶4 90↶4, >5-15 cm/s 45↶4.
  • Observations WILD, PARR: 50-65 cm/s 43↶4, <120 cm/s 50↶4, <50-100+ cm/s 41, 10-65 cm/s 45↶4, <20>60 cm/s 45↶4, 40-120 cm/s 9, 30-70 cm/s 40, 10-100 cm/s 8, 47 cm/s 15, PARR (0+): range 0-82.3 cm/s, average 24.7±1.5 cm/s 46, PARR (1-2): range 0-55.4 cm/s, average 22.9±-1.9 cm/s 46, 1-36 cm/s: Catamaran Brook, New Brunswick, Canada 11.
• Velocity preference and discharge:
  • WILD: decreasing number of PARR with increasing discharge (low 3.2 cm³/s, medium 6.3 cm³/s, high discharge 13 cm³/s) 55. PARR moved deeper and farer from nearest conspecific with increasing discharge 55.
  • WILD: JUVENILES moved from pool to riffle habitats at higher discharge 130↶47 and to pools at low discharge 50↶47. SMOLTS sought lower water velocities with high discharge 131↶60.
• Velocity preference and density:
  • WILD: higher density of mixed-size PARR (age 0 and age 1-2) in riffles (average 26.6 cm/s) than runs (average 17.3 cm/s) 46.
  • LAB: when given the choice between pools (depth 12-16 cm, water velocity 5-10 cm/s) and riffles (depth 3-6 cm, 4-35 cm/s), JUVENILES (age 0+) preferred pools at low density (6 IND/m²), riffles at medium density (12 IND/m²) and were indifferent between pools and riffles at high density (18 IND/m²) 23.
• Velocity and low temperatures: avoids high velocity at low temperatures:
  • WILD: JUVENILES-ADULTS used snout velocities <10 cm/s during autumn 49↶4. JUVENILES chose slower-flowing water at low temperatures 132↶4.
  • WILD, PARR: tendency to leave fast-flowing brooks 41 and avoid fast velocities 6 with decreasing temperatures.
• For velocity and...
  ...redd construction ➝ D1,
  ...territoriality ➝ D3.

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• Observations WILD, FRY: 0+ <0.1 km 41, <0.005 km 34.
• Observations WILD, PARR: <0.005-0.023 km 35.
• WILD: in river Tverrelva (Norway) with width 3-4 m and predominantly 10-30 cm riffle areas, 40% 1+ year old PARR moved further than 75 m up- or downstream (out of observation section). Of remaining 60%, PARR moved maximally 62.5 m up- or downstream, majority within 12.5 m length, i.e. 40-50 m² 42.
• WILD: in river Teno (Finland) and main tributaries, mainly JUVENILES of age 0+ to 2+; in tributary brooks, mainly PARR of age 2+ to 4+. Except for one brook, increasing number of 3+ PARR upstream in brooks (up to 8+ km), decreasing number of 1+ PARR upstream (up to 3 km). Suggests that 3+ PARR actively migrate, probably to a) find better environmental conditions (coarser substrate, deeper and faster water) and food resources and b) flee from predators 41.
• WILD: SMOLTS migrate from the spawning ground along freshwater rivers of 1-1,800 km length 30 to sea (➝ D13). At sea, SMOLTS stayed close to the shore if food abundance in the adjacent estuary was high 133↶60.

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• Depth range in the wild: 0.05-6.5 m:
  • Observations WILD, FRY: <25 cm 43↶4 134↶4 129↶4, 20-40 cm 50↶4, 0.05-1 m 44↶4, <10 cm 45↶4, 20-39 cm 34.
  • Observations WILD, PARR: 25-60 cm 43↶4 49↶4, median of 2 m 135↶39, 15-55 cm 128↶9, 20-70 cm 44↶4 9, 10-70 cm 41, 1-1.5 m 41, >0-3.5 m 7, <3.5 m 6, <1.3 m 9, 30-50 cm 136↶8, 0.1-1.5 m 8, 20-39 cm 34, 0.2-3.2 m 35, 14.6-78.7 cm: Catamaran Brook, New Brunswick, Canada 11.
  • Observations WILD, post-SMOLTS: 0-6.5 m, average 0.5-2.3 m 39.
  • WILD: at sea, KELTS seem to stay close to the surface 120↶60 122 which may be beneficial to reduce osmoregulatory demands, as shallow layers are lower in salinity 39.
  • For depth and redd construction ➝ D1.
• Depth in cages or tanks: use the complete depth available:
  • Observations LAB, SMOLTS: 6-10 m 19.
  • Observations FARM, ADULTS: 15 m 87, 5 m 113.
• Depth preference:
  • WILD, JUVENILES: highest preference at water depth of 30 cm and mean flow velocity of >30 cm/s 34.
• Depth and daily rhythm: moves deeper in the water column during the day than during the night:
  • Observations WILD: PARR 137↶39 138↶39 139↶39 140↶39.
  • Observations WILD, post-SMOLTS: individual differences, though 39.
  • WILD, JUVENILES-ADULTS: move deeper during the day, probably to minimise predation risk from avian predators 141↶39.
  • FARM, ADULTS: moved deeper during the day, probably to avoid high light intensities. Individual differences, though 87.
• Depth and low temperatures: stays in warmer layer at low temperatures:
  • WILD: individuals primarily used riffle-run habitats (average depth 40.9-48.9 cm) over pools in winter 56↶4.
  • WILD: PARR took higher position in water column during day than during night in winter (-0.5-0.2 °C) but avoided shallow water (<100 cm) 6.
  • WILD: post-SMOLTS in the Baltic sea prefer to stay at sea surface temperatures of 9-11 °C 115↶60 142↶60.
  • LAB: in a 15 m deep cage, SMOLTS stayed in the warm surface layer (<3 m, 9-14 °C) 19.
• Depth and high temperatures:
  • WILD: JUVENILES increased their use of runs rather than pools and riffles as temperatures increased 130↶4.
  • FARM: at night and water temperatures of 13-20 °C, PARR crowded at the surface to avoid deeper warmer layers, whereas at temperatures of 8-14 °C, they avoided cooler surface water 87.
• Position in habitat and age:
  • WILD, PARR: tendency to increase distance from shore (horizontal axis) as well as bottom (vertical axis) with increasing age – independent of available depth. Probably trade-off between competitive ability, food availability (higher the higher the water current, and this increases with distance from shore and bottom), and predation risk 7.
  • WILD: older PARR (>10 cm) moved deeper and to faster current velocities (correlated with drift rate) during the day than during the night, younger PARR (≤10 cm) moved deeper and to faster current velocities at night. Whereas older PARR stayed close to structures in the channel (where drift rates were higher compared to open areas), younger PARR kept larger distance 55.
  • For depth and subordination ➝ D16.
• Depth and light intensity: moves deeper after a sudden change in the light environment:
  • Observations WILD: 143↶39.
  • Observations FARM, JUVENILES-ADULTS: 144↶111 145↶111 146↶111 113.
  • Observations LAB, ADULTS: 111.
• Depth and noise: ➝ D17.
• Depth and threat:
  • LAB: equal increase in activity and equal move to lower water vertical position after pretended predator attack in hatchery-reared and wild-caught PARR, both equally reared from egg to 1+ or 2+ years. 1+ year PARR moved deeper than 2+ year 147.

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• Hatched ALEVINS stay in their freshwater territory 148↶63 8 through FRY and PARR stages for up to 5 years:
  • Observations WILD: 2-4 years: Magaguadavic river, New Brunswick, Canada 1, average 3 years: Catamaran brook, New Brunswick, Canada 149↶92, ≤5 years: river Teno and tributaries, Finland 41, 2-5 years 33, 2-3 years 150.
• When a proportion of the population has undergone seawater adaptation, the now called SMOLTS migrate along freshwater rivers of 1-1,800 km length to the sea 30 in spring:
  • Observations WILD: spring to early summer 83↶13, spring 151, March-June 33.
• After up to 4 years, in winter, individuals return as GRILSE to their rivers of origin to spawn:
  • Observations age WILD: 1+ years 151 92 150, ≤4 years 33.
  • Observations season WILD: Oct-Nov, Catamaran brook, New Brunswick, Canada 152↶92, Oct-Jan 33.
• Although some may return to the sea as KELTS, most die of exhaustion 60.
• For migration and temperature ➝ D18.

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• Observations yolk sac absorption: during ca 300 degree days 33.
• Observations TOTAL LENGTH: no data found yet.
• Observations weight: no data found yet.

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• ALEVINS that opened their mouth and began exogenous feeding 16 151.
• Observations length WILD: <35 mm fork length 92.
• Observations weight: no data found yet.

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• Parr: 0-5 years, <5-12.6 cm:
  • FRY from first summer after hatching on 60.
  • Observations age and TOTAL LENGTH WILD: 0+ years: <5 cm, 1+ years: 5-8.4 cm, 2+ years: >8.4 cm 92, average 4.4-11.4 cm 40, 8.4-12.6 cm 35.
  • PARR with >10 cm length at the end of a growth season will usually smoltify the next spring 60, at 2-5 years (➝ D13).
  • Observations weight: no data found yet.
• Smolt: 2-5 years:
  • Observations age: ➝ Parr.
  • Observations TOTAL LENGTH: no data found yet.
  • Observations weight: no data found yet.

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• Maturation and PHOTOPERIOD manipulation:
  • FARM, JUVENILES: only those 0+ males matured that experienced natural PHOTOPERIOD in the “maturation window” in February combined with elevated temperatures in their first year of growth. Males that experienced ambient temperatures or advanced PHOTOPERIOD did not mature 154.
• Maturation and temperature manipulation: no data found yet.

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• Grilse:
  • Adults that return to home river after spending at least one winter at sea 60.
  • Observations age and TOTAL LENGTH WILD: 2-9 years D13, spawning female length: >50<90 cm 14, average length of males and females: 63.9 and 67.8 cm 37.
  • Observations age and weight FARM: 30 months, 2-4 kg 155.
• Kelt:
  • Grilse surviving spawning, may migrate to sea and return for spawning but more likely die of weakness 60.
  • Observations age: 3-9 years D13.
  • Observations TOTAL LENGTH: no data found yet.
  • Observations weight: no data found yet.

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• FARM: size-grading of SMOLTS in 105-120 m³ cages led to an increase of average weight (0-51%) in 13 of 17 cages and a decrease (-5 to -11%) in four cages, all in all an average increase of 14% 156.

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• Otolith deformations and hearing loss:
  • WILD/LAB: higher proportion of sagittal otoliths containing vaterite in hatchery-reared JUVENILES from Norway (ca 41% versus 10%) than in wild-caught JUVENILES from 21 Norwegian rivers. Frequency of at least one vaterite otolith per individual increased with age from 66% at mean 33 g and 7 months (small JUVENILES) to 100% at mean 4,658 g and 18 months (large JUVENILES). Vaterite otoliths were on average 17% larger and 8% lighter than normal aragonite ones. Otoliths containing vaterite lost oscillation amplitude compared to aragonite ones, impairing response to sound. Loss increased with increasing percentage of vaterite from 29% loss at 708 Hz for small and at 583 Hz for medium JUVENILES to 51% loss at 522 Hz for large JUVENILES. Loss in 1-20 Hz infrasound range: 19-35%. Proportion of vaterite otoliths in ADULTS: 30% in Canada, 57% in Australia, 58% in Scotland, 64% in Chile, indicating that hearing loss due to otolith deformations and resulting reduction in welfare is worldwide problem 157.

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• Redd construction and substrate: grain size maximally 10% of female's body length, <1-100 mm, 2.3-29.3% fine material (<1-2 mm):
  • Observations grain size WILD, ADULTS: 0.8-40 mm, 7-9% of body length 158↶159, 100 mm 160↶4, average 20.7 mm 37, median 11.5 mm 38, median 29.2-64 mm 53.
  • Observations fine material WILD, ADULTS: average 3.3-12.5% <1 mm: several rivers in England and Wales 14, 2.3-8% <1 mm: Girnock Burn, Scotland 37, 9.4-17.8% <2 mm: river Bush, Northern Ireland 36, 23% <2 mm: Newmills Burn, Scotland 38, average 3.3-29.3% <1 mm: Sainte-Marguerite river, Canada 53.
  • WILD, ADULTS: in river with clay ground, female started cutting to prepare redd and omitted site when reached the clay layer 14.
• Redd construction and water velocity: range 0.2-1.1 m/s, average 0.5 m/s:
  • Observations WILD, ADULTS: range 0.4-0.8 m/s, average 0.5 m/s 161↶4, average 0.2-1 m/s 14, range 0.2-1.1 m/s, average 0.5 m/s 37, average 0.5 m/s 38.
• Redd construction and water depth: 5-76 cm:
  • Observations WILD, ADULTS: range 17-76 cm, average 38 cm 161, average 5-50 cm 14, range 10-50 cm, average 25 cm 37, average 26 cm 38.
• Redd construction:
  • WILD, ADULTS: female cut by repeated flexures of her body, increasingly with shorter time to oviposition. Dominant male chased away competing males 14.

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• Spawning substrate: ➝ D1.
• Spawning season: October-January:
  • Observations WILD: October-November 1 152↶92, November-December 38, October-January 33.
• Spawning (day)time: no data found yet.
• Spawning temperature: no data found yet.
• Spawning salinity: fresh water ➝ D13 D1.
• Spawning and water velocity: ➝ D1.
• Spawning depth: ➝ D1.
• Spawning density: no data found yet.

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• Number of redds:
  • Observations WILD, ADULTS: average 1 redd per female 37,
• Fecundity per redd: 17-450 eggs:
  • Observations absolute fecundity WILD, ADULTS: 17-42 eggs 14, median 450 eggs 38.
  • Observations relative fecundity: no data found yet.

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• WILD, ADULTS: after female spawning, female cut quickly to cover eggs in gravel in one or more egg pockets per redd 14 which protects them from light, predators, and high water flow 14 59↶47.

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• FARM, ADULTS: sensitive to blue light at low intensity (0.82 μmol/m²/s) at night: dived away to cage bottom. At medium (26.8 μmol/m²/s) and high (35.4 μmol/m²/s) intensity: fast swimming and collisions with conspecifics and cage (probably temporarily blinded), jumped 18 times more than at low intensity or without light 113.

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• For vision and foraging ➝ D4.

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• Olfaction and navigation:
  • WILD, JUVENILES-ADULTS: speculation that individuals navigate through the sea by sensing the earth's magnetic field through magnetic particles in either their olfactory system 162↶60 or in their lateral line 163↶60 or a combination of both. Only when coming close to the river mouth, do they go by olfactory cues 164↶60 165↶60.
  • FARM: SMOLTS brought to the sea in a tank could not follow the river flow and imprint on the scent of the water: did not return to exact location but moved towards the general area of the river 166↶60. Homing, usually, is so accurate that restocking measures have to specify the exact location to where salmons ought to return, not just a random section of the river 167↶60.

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• Hearing type:
  • LAB, ADULTS: hearing GENERALIST 26.
• Hearing spectrum:
  • LAB, SMOLTS: under quiet sea conditions, sensitive to sound from 30-380 Hz, greatest sensitivity at 160 Hz. More sensitive to sounds in water (high particle motion) than in air. Loud speaking in close proximity and footsteps in the substratum on the shore will most likely be heard. Swim bladder is far removed from the skull (opens into the gut) and thus most likely is not involved in hearing 26.

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• FARM, ADULTS: at infrasound of 12.5 Hz, erratic swimming, deep diving, increased swimming activities, three times greater swimming speed. Dropping a disc on the water surface caused descend to depths of 1.5-2 m and twice as high swimming speed. ADULTS are potentially able to habituate to regular disturbance, though 113.

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• Lateral line system and sensing water movement and vibrations:
  • Detects local water movements, so that individual perceives and localises prey, enemies, and sexual partners 170↶171.
  • Detects surface and low frequency waves in the vicinity of the fish body, indirectly detects vibrations from sound waves 172↶171.
  • For lateral line and navigation ➝ D26.

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• FARM: in 10 x 10 m cages (15 m deep), 500 SMOLTS separated into two schools at different cage depths, 4-6 m and 6-11 m 19.

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• WILD: after one month in a river, hatchery-released PARR kept higher densities (average 0.35 versus 0.06 IND/m²) than wild PARR 15.

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• FARM, SMOLTS: decreasing welfare score (with fin condition and condition factor contributing positively, plasma cortisol and plasma glucose contributing negatively) with increasing stocking density. Certain variability of welfare at densities 10-21 kg/m³. From ca 22 kg/m³ on, welfare decreased 156.

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• Inverse relation:
  • WILD, PARR: the higher the density (0.01-1.7 IND/m²) the lower the growth – power curve with steepest decrease at low densities 173.
• Direct relation:
  • LAB: in 50 cm deep tanks with 78 cm diameter, age 1+ PARR had lower weight, length, and body condition when held at 8 kg/m³ than at 30 kg/m³ 25.

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• Hierarchy and group size: no data found yet.
• Establishing hierarchy: no data found yet.
• For dominance ➝ D5, for subordination ➝ D16.

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• Features of dominance:
  • LAB: dominant FRY stayed in place where food accumulates, were highly mobile in that area, and showed more aggressive behaviour than subordinate FRY 20.
• Hierarchy and time of emergence:
  • LAB: among nine pairs of similar-weighted early and late emerging FRY, five early and four late emerging FRY became dominant 20.
• Hierarchy and weight:
  • LAB: initiators of aggression among 1+ year old PARR with higher weight (average 108.8 g versus 89.6 g) than receivers 21.

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• Features of subordination:
  • LAB: to avoid confrontations with higher-ranked individuals, subordinate FRY displayed vertical swimming in the upper water level, hardly moved in the tank, and kept a position away from food 20.
• Hierarchy and stress: no data found yet.

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• Direct relation:
  • LAB, FRY: increasing density in pools (6, 12, or 18 IND/m²) increased aggression in the form of intentional movements, nips, chases, and displays 23.
• No effect:
  • LAB: not much aggression via chasing, charging, displacement, or fin-nipping among 2+ PARR in densities of 15, 25, or 35 kg/m³ 24.
• Inverse relation:
  • LAB: more aggression via fin biting among 1+ PARR at a density of 30 kg/m³ than at 8 kg/m³. Total amount of aggression (attacks, displacements, fin biting), though not as severe, was higher at low density 25.

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• LAB, PARR: no effect of husbandry disturbance (tank cleaning and staff passing by the tank) at density of 25 kg/m³, highest average welfare. At 15 kg/m³ and 35 kg/m³, high and middle-high disturbance affected welfare positively, whereas lower disturbance was detrimental to welfare. Probably more direct aggression at low density and more aggression following collisions at high density that is suppressed by the external disturbance, similar to a predator or larger conspecific 24.

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• WILD: PARR occupied optimal habitats with fast current velocity and high drift rates at low densities (average 0.06 IND/m²) and displayed low levels of aggressiveness 15.
• WILD: during 40 min observation period, PARR visited 3-26 foraging stations (median 12.5) within territories of mean 0.3-4.5 m², travelling 15.7-95.0 m (median 39.3 m) within territory. Foraged at station 0.9-48 times before switching every 10 min to every 12.9 s. Distance travelled mainly determined by foraging and switching stations (96.6%) before chasing (3%) and fleeing intruders (0.4%). Territory size decreased with increasing current velocity and increased with larger depth. Number of foraging stations did not increase with decreasing velocity. Relationship between total distance travelled and velocity is curvilinear: largest distance travelled at intermediate velocity. Highest aggression at intermediate velocity: Catamaran Brook, New Brunswick, Canada 11.

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• LAB: in a group of 5, ADULTS learned to associate a conditioned stimulus (a sound) – in place of the unconditioned stimulus of a mild electric shock – with a conditioned response (stress = change in the heart beat). Allowed determination of hearing spectrum (➝ D27) 26.

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• Adaptation and feeding:
  • WILD: adaptation to hatchery conditions hindered fast adaptation to wild habitat in 2+ year old PARR: after one month in a river, hatchery-released PARR consumed 20-30% more poor quality food (exuvia, algae, detritus, sand) than wild PARR, missed more drift items especially in fast current velocities, fed more on benthic than on drift prey, had lower stomach fulness (82% versus 94%) 15.

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• Stress coping and subordination:
  • LAB: JUVENILES with low growth rate prior to experiment released more cortisol when confined for 30 min in 0.6 L chamber than JUVENILES with high growth rate, indicating relationship between subordination and stress coping style 27.
• Stress coping and locomotion:
  • LAB: JUVENILES of different families differed in locomotor activity and cortisol release (average 2.1-6.6 ng/g/h) during confinement for 30 min in 0.6 L chamber, indicating different stress coping styles and heritable hypothalamus-pituitary-interrenal responsiveness. Families moving longer also released more cortisol, indicating higher stress levels. Families moving longer and releasing more cortisol also displayed lower resistance towards infectious pancreatic necrosis, no correlation with furunculosis. No difference between families in feeding resumption or feed intake during four weeks of isolation 27.

^{In the structure of menu item 16 and the definition of "SHYNESS-BOLDNESS", we follow 174.}

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• Boldness and time of emergence:
  • LAB: latency to eat first pellet decreased over five days of isolation, similar for early and late emerging FRY. On days 4 and 5, early emerged FRY ate first pellet sooner than late emerged FRY. Decreasing latency and difference in FRY of different time of emergence (on days 8, 9, and 10) held in second experiment five months later. Number of pellets consumed increased over five days of isolation, similar for early and late emerged FRY. On days 4 and 5, early emerged FRY ate more than late emerged FRY. Increasing amount of pellets consumed held in second experiment five months later. Faster food resumption in early emerged FRY after move to new environment and under isolation suggests boldness, but no difference in oxygen consumption, cortisol levels (➝ D28), and social status (➝ D5 D16) between early and late emerged FRY refute hypothesis of proactive and reactive coping styles 20.

^{In the structure of menu item 16 and the definition of "EXPLORATION-AVOIDANCE", we follow 174.}

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• For aggressiveness and...
  ...dominance ➝ D5,
  ...subordination ➝ D16,
  ...stocking density ➝ D29.

^{In the structure of menu item 16 and the definition of "AGGRESSIVENESS", we follow 174.}

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• LAB: FRY confined to 50 mL containers for 30 min had higher cortisol levels than unstressed FRY. No difference between early and late emerging FRY 20.

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• Crowding and chilling:
  • FARM: ADULTS in 1,000 m³ net-pen at density 20 kg/m³ killed by blow to head, gill cut, transferred to bleeding tank with 1 °C seawater at density 75 kg/m³ for 60 min. Second group transferred to 1 m³ chilling tank with 1 °C seawater at density 75 kg/m³ for 60 min before slaughter. Higher plasma cortisol in live-chilled (ca 1 mmol/L versus 0.3 mmol/L) compared to unchilled group. Even higher cortisol level (ca 1.3-1.5 mmol/L) after 24 h crowding in net-pen at density 200 kg/m³ and stressed by reducing water level to increase density to 500 kg/m³ for 5 min every 6 h; no difference if additionally live-chilled. Highest rigour scores at ca 8 h after slaughter in unchilled (ca 3.8-4.3 versus 2.8-3.3 where 1 means no rigour, 5 means full rigour) compared to chilled groups, regardless of crowding. Unchilled groups reached highest rigour scores earlier (at ca 8 h versus 18 h) than chilled groups. Higher muscle glycogen in uncrowded (ca 1.7 g/kg versus 0.5 g/kg) than crowded groups regardless of chilling, indicating higher energy depletion in crowded groups 155.

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• Cage submergence:
  • LAB, SMOLTS: cutting off access to air by submerging the sea-cage caused jumping behaviour 19 111. Increasing the time of submergence 19 and exposition to light or feed during submergence 111 increased the number of jumps. Submerged SMOLTS increased swimming speed, probably to create hydrodynamic lift to avoid sinking, and did not display buoyancy control problems or tilted swimming (indicating stress) in 10 x 10 x 11 m cages. Submergence did not affect appetite – the slightly lower growth could be due to lower temperatures in the deeper water layer and went away when on-grown for three months in a re-surfaced cage 19.
  • Application of cage submergence: counter-measurement to short-term (bad weather conditions) or long-term (algal-bloom, low temperatures) detrimental surface conditions 19. Also a stress-free method for delousing from sea lice when jumping individuals break water surface with floating chemical therapeutant infused in oil 111.

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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) 175.

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• Time to loss of visual evoked response (response to flash of light to stimulate retina of eye):
  a) percussive stunning: LAB, ADULTS: 0-1 min if the blow is administered correctly and with sufficient force 176,
  b) spiking: LAB, ADULTS: 0-1 min if the stab is administered correctly and with sufficient force 176,
  c) exsanguination by gill-cutting (without prior stunning): LAB, ADULTS: 2.5-7.5 min 176,
  d) stunning by carbon dioxide narcosis: LAB, ADULTS: 3-9 min, accompanied by vigorous movements, fast swimming, and escape attempts 176.

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• Percussive stunning to be preferred over spiking, because individuals do not have to be removed from water – possibly maximal prevention of suffering. No evidence of improved meat quality for exsanguination without prior stunning, so prior stunning would improve welfare without loss of quality. Because immobilisation through carbon dioxide narcosis sets in before loss of sensibility, risk of being sensible at exsanguination 175.

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