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Atlantic salmon

Salmo salar
Salmo salar (Atlantic salmon)
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Distribution
Distribution map: Salmo salar (Atlantic salmon)

IUCN Red List status  
least concern



Information

Authors: Jenny Volstorf, Maria Filipa Castanheira
Version: C | 2.0 (2023-05-11)

Please note: This part of the profile is currently being revised.


Reviewers: N/A
Editor: Jenny Volstorf

Initial release: 2016-11-26
Version information:
  • Appearance: C
  • Last major update: 2023-05-11

Cite as: »Volstorf, Jenny, and Maria Filipa Castanheira. 2023. Salmo salar (WelfareCheck | farm). In: fair-fish database, ed. fair-fish. World Wide Web electronic publication. Version C | 2.0. https://fair-fish-database.net.«

WelfareScore | farm

Salmo salar
LiPoCe
Criteria
Home range
score-li
score-po
score-ce
Depth range
score-li
score-po
score-ce
Migration
score-li
score-po
score-ce
Reproduction
score-li
score-po
score-ce
Aggregation
score-li
score-po
score-ce
Aggression
score-li
score-po
score-ce
Substrate
score-li
score-po
score-ce
Stress
score-li
score-po
score-ce
Malformations
score-li
score-po
score-ce
Slaughter
score-li
score-po
score-ce


Legend

Condensed assessment of the species' likelihood and potential for good fish welfare in aquaculture, based on ethological findings for 10 crucial criteria.

  • Li = Likelihood that the individuals of the species experience good welfare under minimal farming conditions
  • Po = Potential of the individuals of the species to experience good welfare under high-standard farming conditions
  • Ce = Certainty of our findings in Likelihood and Potential

WelfareScore = Sum of criteria scoring "High" (max. 10)

score-legend
High
score-legend
Medium
score-legend
Low
score-legend
Unclear
score-legend
No findings

General remarks

Salmo salar is a salmonid from both coasts of the northern Atlantic, migrating into boardering rivers to spawn. It is the most frequently farmed fish in Europe which represents 50% of the worldwide S. salar production. Upbringing in fresh water, predominantly in flow-through tanks, lasts for 1-1.5 years after which smoltification prepares the individuals for life in seawater; on-growing in sea cages covers 50-70% of the life cycle. Where the culture site does not provide suitable conditions for sea transfer, individuals are grown out in land-based freshwater RAS to harvestable size. Individuals are slaughtered before reaching maturity. Adults destined to become broodstock are transferred back to freshwater about 2 months before spawning. The underlying migration habit is one of the factors very hard to accommodate in captivity, as it is unclear whether it is sufficient to provide the species with the conditions of the respective life stages or whether it needs to experience the transition. Other factors responsible for the low FishEthoScore are substrate needs as well as high levels of aggression, stress, and deformations under farming conditions. Avoiding manipulation to induce spawning, providing substrate, and applying the high-standard slaughter methods are ways towards improving welfare for S. salar in captivity.

Note: LARVAE are called ALEVINS; JUVENILES are called PARR in fresh water and SMOLTS after bodily modification to sustain seawater; SPAWNERS are called GRILSE at first spawning and KELTS thereafter (very rare). We added “ADULTS” for the case when it is not clear whether SMOLTS or GRILSE are meant. As individuals are usually slaughtered before reaching maturity, “ADULTS” in farms refers to ADULTS to become SPAWNERS, i.e., during holding before/between the spawning event(s).

1  Home range

Many species traverse in a limited horizontal space (even if just for a certain period of time per year); the home range may be described as a species' understanding of its environment (i.e., its cognitive map) for the most important resources it needs access to.

What is the probability of providing the species' whole home range in captivity?

There are unclear findings for minimal and high-standard farming conditions, as the missing wild information at sea does not allow a comparison with farming conditions. Our conclusion is based on a medium amount of evidence.

Likelihoodscore-li
Potentialscore-po
Certaintyscore-ce

Eggs: does not apply.

ALEVINS and FRY:

  • WILD: mainly within 20 m from redd 1. FRY: most moved 1-5 m from redd 2.
  • FARM: ALEVINS: vertical trays with variable size frames: 0.6 m (Aquatec.com). FRY: tanks: 1-10 m ∅ 3; raceways 3.
  • LAB: does not apply.

PARR and SMOLTS:

  • WILD: PARR: mainly 37.5-50 m2, some 300+ m2 4, mainly <5 m 5 6, ≤23 m 6. Non-ANADROMOUS strain: 95% range 3-44,408 m2 7. SMOLTS: no data found yet.
  • FARM: PARR: most frequently flow-through freshwater tanks, but also flow-through freshwater raceways, recirculated freshwater tanks or raceways, freshwater cages 3. Tanks: 2-15 m ∅ 3, 14-20 m ∅ for growth to harvestable size 8; freshwater cages: 9-15 m2, 10-25 m ∅ 3. SMOLTS: sea cages: 576 m2 (24 x 24 m) or 100 m ∅ 9, 125 m2 (15 x 15 m) 10, 100 m2 (10 x 10 m) 11, first 9-20 m2, then 81-400 m2 3, 160 m ∅ 3, 40-50 m ∅ 12.
  • LAB: does not apply.

ADULTS:

  • WILD: no data found yet.
  • FARM: sea cages: 576 m2 (24 x 24 m) or 100 m ∅ 9, 125 m2 (15 x 15 m) 10, 100 m2 (10 x 10 m) 11, first 9-20 m2, then 81-400 m2 3, 160 m ∅ 3, 40-50 m ∅ 12; tanks: 14-20 m ∅ for growth to harvestable size 8.
  • LAB: does not apply.

GRILSE and KELTS:

  • WILD: redd: ellipsoid with 0.5-6 x 0.5-4 m at maximum points 13. Move 0.3-2.1 km after spawning 14.
  • FARM: holding in sea cages or tanks, moved to freshwater tanks ca 2 months before spawning 9 3. Tanks: 10-25 m ∅ 3.
  • LAB: does not apply.

2  Depth range

Given the availability of resources (food, shelter) or the need to avoid predators, species spend their time within a certain depth range.

What is the probability of providing the species' whole depth range in captivity?

It is low for minimal farming conditions, as some trays and tanks do not cover the whole range in the wild. It is medium for high-standard farming conditions, as other trays and tanks cover the range in the wild, although we cannot be sure in GRILSE and KELTS. Our conclusion is based on a medium amount of evidence, as farm information for GRILSE and KELTS is missing.

Likelihoodscore-li
Potentialscore-po
Certaintyscore-ce

Eggs:

  • WILD: no data found yet.
  • FARM: no data found yet.
  • LAB: does not apply.

ALEVINS and FRY:

  • WILD: ALEVINS: in gravel, for spawning depth → GRILSE and KELTS. FRY: mainly 0.2-0.4 m 15 16 17 5, range 0.06-0.5 m 15, in artificial stream: mainly <0.2 m 18.
  • FARM: ALEVINS: hatchery trays and tanks: 0.2-0.5 m 19, trays: 0.1 m 3. FRY: tanks: 1.5 m 3.
  • LAB: does not apply.

PARR and SMOLTS:

  • WILD: PARR: mainly 0.2-0.4 m 15 16 17 6, ≤0.6 m 17 6, range 0.06-0.5 m 15, range 0.2-1 m 17, in artificial stream: 0.05-0.5 m 18. Non-ANADROMOUS strain: mostly <0.6 m, sometimes >1 m 7. SMOLTS: at sea, caught in trawl 0-10 m, actual depth use might be shallower 20, hatchery-reared IND released in Fjord: mainly 1-3 m, <0.5 m at night, irregular dives ≤6.5 m during the day 21.
  • FARM: PARR: tanks: 0.3-0.9 m until free swimming, then ≤3 m 3, 3.5-4.5 m for growth to harvestable size 8; freshwater cages: 3-5 m 3. SMOLTS: sea cages: 15-18 m 9 10 11 22, 5-50 m 3 12. In 15 m sea cage, IND stayed mostly in 0-3 m where temperature was the warmest 11. Learned to use full depth when cage was submerged 11. Depth use increased during daytime and for thermoregulation 22.
  • LAB: does not apply.

ADULTS:

  • WILD: no data found yet.
  • FARM: sea cages: 15-18 m 9 10 11 22, 5-50 m 12. In 15 m sea cage, IND stayed mostly in 0-3 m where temperature was the warmest 11. Learned to use full depth when cage was submerged 11. Depth use increased during daytime and for thermoregulation 22. Tanks: 3.5-4.5 m for growth to harvestable size 8.
  • LAB: does not apply.

GRILSE and KELTS:

  • WILD: spawn at mean 0.2-0.5 m 23 13 24 25. KELTS: during migration back to the sea mostly within 1 m, occasionally to 3 m, seldomly to 15 m 26, mean 2 m, 94% within 5 m, max 83 m 27.
  • FARM: no data found yet.
  • LAB: does not apply.

3  Migration

Some species undergo seasonal changes of environments for different purposes (feeding, spawning, etc.), and to move there, they migrate for more or less extensive distances.

What is the probability of providing farming conditions that are compatible with the migrating or habitat-changing behaviour of the species?

It is low for minimal farming conditions, as both strains undertake more or less extensive migrations, and we cannot be sure that providing each age class with their respective environmental conditions will satisfy their urge to migrate or whether they need to experience the transition. It is medium for high-standard farming conditions, as the non-ANADROMOUS strain at least does not migrate between sea- and fresh water and the range in captivity potentially overlaps with the migration distance (although unknown). Our conclusion is based on a medium amount of evidence.

Likelihoodscore-li
Potentialscore-po
Certaintyscore-ce

Mostly ANADROMOUS 28 29 30 31 32, sometimes also non-ANADROMOUS 33 34 35 7.

ANADROMOUS strain:

Eggs: does not apply.

ALEVINS and FRY:

  • WILD: in natal rivers for ≤5 years 36 37. 0.1-26 °C 15, 10-18.5 °C at emergence from gravel 2, fresh water 15 2.
  • FARM: ALEVINS: near darkness until first feeding, 8 °C, fresh water 3. Incubators: tendency of increasing cortisol with increasing artificial light at night (0.1-8 lux), but depends on the analysis method applied 38. FRY: 12 °C at first feeding, fresh water 3. For details of holding systems → F1 and F2.
  • LAB: no data found yet.

PARR and SMOLTS:

  • WILD: PARR: in natal rivers for ≤5 years 36 37 31 39 40. Some older IND migrate into lakes 34 or smaller tributaries 36. 0.1-26 °C 15 36, 14-23 °C 40, fresh water 15 36 40. SMOLTS: after seawater adaptation, migrate along freshwater rivers to the sea 29 32. At sea, based on distribution 20, estimated 0-24 h PHOTOPERIOD. At sea, 6-12 °C, 34-35.3 ppt 20.
  • FARM: PARR: tanks: fresh water, 0.5-2.5 body lengths/s current 3. SMOLTS: sea cages: artificial light by submerged lamps in winter is supposed to increase day length and therefore growth and prevent early maturation 3. For details of holding systems → F1 and F2.
  • LAB: SMOLTS: cages: stressed by blue light 41.

ADULTS:

  • WILD: some mature in rivers as PARR 42 (10-57%) 39 (12.4%) 43 or SMOLTS 43, most mature at sea 28 39 and stay for ≤3 years 30 31 39 44. At sea, based on distribution 20, estimated 0-24 h PHOTOPERIOD. At sea, 6-12 °C, 34-35.3 ppt 20.
  • FARM: sea cages: artificial light by submerged lamps in winter is supposed to increase day length and therefore growth and prevent early maturation 3. For details of holding systems → F1 and F2.
  • LAB: no data found yet.

GRILSE and KELTS:

  • WILD: return from sea to natal river to spawn 14 30 31. Most die of exhaustion after spawning 14 45. Some (10%) 33 migrated as KELTS back to the sea 26 27 and even fewer migrated upriver again for another spawning event 26.
  • FARM: tanks: <8 ppt 3. For details of holding systems → F1.
  • LAB: no data found yet.

non-ANADROMOUS strain:

Eggs: does not apply.

ALEVINS and FRY:

  • WILD: in small ponds, fresh water 33 or tributaries 46.
  • FARM: ALEVINS: near darkness until first feeding, 8 °C, fresh water 3. Incubators: tendency of increasing cortisol with increasing artificial light at night (0.1-8 lux), but depends on the analysis method applied 38. FRY: 12 °C at first feeding, fresh water 3. For details of holding systems → F1 and F2.
  • LAB: no data found yet.

PARR:

  • WILD: in small ponds, fresh water 33 or streams 34 7. Some older IND migrate into lakes until maturation 34 46. 
  • FARM: tanks: fresh water, 0.5-2.5 body lengths/s current 3. For details of holding systems → F1 and F2.
  • LAB: no data found yet.

ADULTS:

  • WILD: in small ponds, fresh water 33 or migrating from lakes back into streams 34.
  • FARM: → PARR.
  • LAB: no data found yet.

SPAWNERS:

  • WILD: spawn in tributaries 46.
  • FARM: tanks: <8 ppt 3. For details of holding systems → F1.
  • LAB: no data found yet.

4  Reproduction

A species reproduces at a certain age, season, and sex ratio and possibly involving courtship rituals.

What is the probability of the species reproducing naturally in captivity without manipulation of these circumstances?

It is low for minimal farming conditions, as the species is manipulated (wild breeders, separation by sex, hormonal/photoperiod/temperature manipulation, stripping). It is medium for high-standard farming conditions, as omitting hormonal manipulation and stripping is easily imaginable but needs verification for the farming context. Our conclusion is based on a medium amount of evidence.

Likelihoodscore-li
Potentialscore-po
Certaintyscore-ce

Eggs: does not apply.

ALEVINS and FRY: does not apply.

PARR and SMOLTS: does not apply.

ADULTS: does not apply.

GRILSE and KELTS:

  • WILD: mature at average 3.2-6.3 years 39 or 2.2-7.8 years 46 depending on latitude; dwarf landlocked females spawned at 3+ years 33, range of landlocked strains 2.0-6.5 years 46. Spawn October-January 37. Dominant male courts female by quivering close to her, nudging her mid body, crossing over the female's tail 47↶48 49↶48 50↶48. For nest building → F3.
  • FARM: IND from the wild may be added to the captive breeder population 3. Spawn after 2 years in seawater 3. After being moved from sea cages to freshwater tanks shortly before spawning, kept in mixed-sex groups 3. Sometimes hormone manipulation to synchronise spawning 3. PHOTOPERIOD and temperature manipulation to simulate spawning conditions that goes beyond shifting of natural cycle 3. Stripping of eggs and milt 9 19 3, sometimes surgically under lethal anaesthesia 3.
  • LAB: dominance rank correlated with body weight, fork length, and kype size 51. Dominant males approached and mated with females more frequently than subordinate ones 51.

5  Aggregation

Species differ in the way they co-exist with conspecifics or other species from being solitary to aggregating unstructured, casually roaming in shoals or closely coordinating in schools of varying densities.

What is the probability of providing farming conditions that are compatible with the aggregation behaviour of the species?

It is low for minimal farming conditions, as – even in the absence of density data in the wild – we may conclude from studies in farms that densities in some tanks are potentially stress inducing. It is medium for high-standard farming conditions, as densities around 20 kg/m3 in cages increase welfare. Our conclusion is based on a medium amount of evidence, as wild information for SMOLTS, GRILSE, and KELTS is missing

Likelihoodscore-li
Potentialscore-po
Certaintyscore-ce

Eggs: does not apply.

ALEVINS and FRY:

  • WILD: live solitary after emerging from the gravel, but remain in the same areas as siblings 2 52, in artificial stream: 1.1-306 IND/100 m2 18.
  • FARM: 50+ kg/m3 9.
  • LAB: no data found yet

PARR and SMOLTS:

  • WILD: PARR: live solitary or in small groups 53, in artificial stream: 9.5-87.6 IND/100 m2 18. SMOLTS: migrate downstream in schools 53 during the day, individually at night 54.
  • FARM: PARR: 40-70 kg/m3 for growth to harvestable size 8. Tanks: lower glucose levels in PARR at 21 and 43 kg/m3 than 65 and 86 kg/m3 before transfer to seawater, thereafter decrease and no differences in sea cages in SMOLTS 55. Decreasing condition factor at 21-86 kg/m3, no difference in PARR before transfer to seawater, then better condition factor at 21 kg/m3 than 86 kg/m3 in sea cages in SMOLTS, leveling out over time 55. After 12 weeks in seawater cages, no differences in growth, condition factor, glucose in SMOLTS 55. SMOLTS: sea cages: usually 20 kg/m3 9, 50 IND/m3 3; 15-25 kg/m3 3. Cages: decreasing welfare score with increasing density from 22 kg/m3 on 56. In 14 m deep cage, preference for 16-18 °C during the day and surface layer during the night resulted in higher density in the respective water layers and thus lower oxygen, even more so at 35 kg/m3 than 15 kg/m3 57. In 15 m deep cage, at 0.7 kg/m3, separated into 2 schools at different depths 11.
  • LAB: PARR: higher welfare at 25 kg/m3 than 15 and 35 kg/m3 58. Lower weight at 8 kg/m3 than 30 kg/m3 59.

ADULTS:

  • WILD: no data found yet.
  • FARM: sea cages: usually 20 kg/m3 9, 50 IND/m3 3; 15-25 kg/m3 3. Cages: decreasing welfare score with increasing density from 22 kg/m3 on 56. In 14 m deep cage, preference for 16-18 °C during the day and surface layer during the night resulted in higher density in the respective water layers and thus lower oxygen, even more so at 35 kg/m3 than 15 kg/m3 57. In 15 m deep cage, at 0.7 kg/m3, separated into 2 schools at different depths 11.
  • LAB: no data found yet.

SPAWNERS:

  • WILD: no data found yet.
  • FARM: 25 kg/m3 60↶55.
  • LAB: no data found yet.

6  Aggression

There is a range of adverse reactions in species, spanning from being relatively indifferent towards others to defending valuable resources (e.g., food, territory, mates) to actively attacking opponents.

What is the probability of the species being non-aggressive and non-territorial in captivity?

It is low for minimal farming conditions, as – even in the absence of aggression data in the wild – we may conclude from studies in labs that some densities and current velocities potentially induce aggression. It is medium for high-standard farming conditions, as innovations to decrease aggression by decreasing density or increasing current velocity need to be verified for the farming context. Our conclusion is based on a medium amount of evidence.

Likelihoodscore-li
Potentialscore-po
Certaintyscore-ce

Eggs: does not apply.

ALEVINS and FRY:

  • WILD: aggressive and territorial after emerging from the gravel 2.
  • FARM: no data found yet.
  • LAB: food competition in groups of 2 61 62 and groups of 10 52. Pools: increasing aggression with increasing density (6 → 18 IND/m2) 63.

PARR and SMOLTS:

  • WILD: PARR: no data found yet. SMOLTS: decreased agonistic and territorial behaviour and increased schooling during downstream migration 64↶35 65↶35, probably induced by changing environmental conditions like increases in water velocity 53↶35.
  • FARM: no data found yet
  • LAB: PARR: tanks: aggressive in groups of 20, more so in IND with high compared to low standard metabolic rate 66. More fin biting at 30 than 8 kg/m3, but more overall aggression (though not as severe) at 8 kg/m3 67. Tanks: aggressive in groups of 10 at 10 kg/m3, more so in IND with restricted feeding ration 68. SMOLTS: raceways (33 ppt): little aggression at current velocity of 0.8 and 1.5 body lenghts/s, higher frequency at 0.2 body lengths/s, but higher frequency of caudal fin erosion at fast than slow velocity 69.

ADULTS:

  • WILD: no data found yet.
  • FARM: no data found yet.
  • LAB: raceways (33 ppt): little aggression at current velocity of 0.8 and 1.5 body lenghts/s, higher frequency at 0.2 body lengths/s, but higher frequency of caudal fin erosion at fast than slow velocity 69.

GRILSE and KELTS:

  • WILD: ANADROMOUS males chase away mature PARR 35.
  • FARM: no data found yet.
  • LAB: male competition for females 51. Females were less aggressive towards males with higher adipose fin index indicating mate choice 51.

7  Substrate

Depending on where in the water column the species lives, it differs in interacting with or relying on various substrates for feeding or covering purposes (e.g., plants, rocks and stones, sand and mud, turbidity).

What is the probability of providing the species' substrate and shelter needs in captivity?

It is low for minimal farming conditions, as the species uses substrate, but many or all farming facilities for each age class are devoid of it. It is medium for high-standard farming conditions a) given hatching substrate for ALEVINS as well as cover and enrichment for PARR in tanks, b) as improvements for GRILSE and KELTS are unlikely, and c) as innovations for enrichment need to be verified for the farming context. Our conclusion is based on a medium amount of evidence, as innovations for cages are missing, for example.

Likelihoodscore-li
Potentialscore-po
Certaintyscore-ce

Eggs:

  • WILD: for redds → GRILSE and KELTS. Decreasing survival of pre-eyed and eyed stages with increasing percentage of silts and clays (<0.06 mm) probably by restricting oxygen consumption 70.
  • FARM: no data found yet.
  • LAB: no data found yet.

ALEVINS and FRY:

  • WILD: ALEVINS: in gravel 13 31 1. FRY: gravel 17 1, pebbles 5, cobbles 5, “home stone” (mean 6.6 cm in summer, mean 17.8 cm in autumn) over which they hovered in summer, under which they hid in autumn 15. Hid behind rocks or in gravel 2, preferred complete over partial or no cover 5.
  • FARM: ALEVINS: trays or troughs with artificial hatching substrate 9 (stones, gravel, astroturf, biomatting, etc.) until yolk sac absorption 19 3. Astroturf increased growth compared to flat-screen rearing 71. FRY: tanks 3, probably without substrate.
  • LAB: FRY reared in tanks with plastic plants and pipes did not differ in exploratory behaviour of a maze from non-enriched IND 72.

PARR and SMOLTS:

  • WILD: PARR: gravel and cobbles 17. Younger IND found in rivers with cobbles and pebbles, older IND with cobbles to boulders 36. “Home stone” (mean 6.4-6.7 cm in summer, mean 20.9-24.4 cm in autumn) over which they hovered in summer, under which they hid in autumn 15. Habitat preference not only determined by substrate but by complex interaction between hydro-geomorphologic, ecologic, and dynamic factors 40. Non-ANADROMOUS strain: mostly gravel to boulder, sometimes fine substrate or bedrock 7. SMOLTS: based on depth (→ F2), probably PELAGIC at sea.
  • FARM: PARR: tanks, often outdoor and thus requiring protection from predators 3, probably without substrate. Tanks: lower stress and higher growth in FRY-SMOLTS with 67% cover 73. Lower mortality after disease outbreak in enriched (variable water inflow, gravel, shelters) than non-enriched tanks 74 75. For details of holding systems → F1 and F2.
  • LAB: PARR: rearing in enriched tanks (pebbles, cobbles, vertically-floating plastic plants) increased neural plasticity and spatial learning (fewer mistakes in maze, faster exit) than in non-enriched tanks 76. Tanks: tendency of better growth with vertically-suspended PVC pipes 77. IND reared in tanks with plastic plants and pipes explored maze more readily than non-enriched IND 72.

ADULTS:

  • WILD: no data found yet.
  • FARM: for details of holding systems → F1 and F2.
  • LAB: no data found yet.

GRILSE and KELTS:

  • WILD: female builds redd 13 24 in gravel substrate 24 with 2.3-12.5% 13 24, ≤29.2% fine material <1 mm 70.
  • FARM: for details of holding systems → F1, for stripping → F4.
  • LAB: no data found yet.

8  Stress

Farming involves subjecting the species to diverse procedures (e.g., handling, air exposure, short-term confinement, short-term crowding, transport), sudden parameter changes or repeated disturbances (e.g., husbandry, size-grading).

What is the probability of the species not being stressed?

It is low for minimal farming conditions. It is medium for high-standard farming conditions, as some innovations to reduce stress need to be verified for the farming context. Our conclusion is based on a medium amount of evidence.

Likelihoodscore-li
Potentialscore-po
Certaintyscore-ce

Eggs:

  • WILD: no data found yet.
  • FARM: no data found yet.
  • LAB: no data found yet.

ALEVINS and FRY:

  • WILD: no data found yet.
  • FARM: FRY: stressed by handling and confinement 38. Incubators: water cortisol levels can be used as a non-invasive method to measure stress 38. For stress and artificial light at night→ F5.
  • LAB: stressed by confinement 62.

PARR and SMOLTS:

  • WILD: no data found yet.
  • FARM: PARR: tanks: size-graded 2-5 times; (freshwater and sea) cages: usually size-graded once 3. SMOLTS: after smoltification, transport to sea by trucks or wellboats 9 3 12. Stressed by transport, especially loading (reducing water level, crowding, pumping) 78. Stressed by crowding and confinement 79. Occasional submergence of cages may counteract detrimental surface conditions (low oxygen levels, storms, ice, algal bloom, sea lice larvae) 11. Acoustic delicing was effective and stressless 80 and is potentially less stressful than other methods, which involve removal from water and handling. For slaughter, crowded in cages, pumped, and slaughtered on site or transported to slaughtering plant 9 81 by wellboat 81. For stress and a) aggregation → F6, b) cover → F3.
  • LAB: PARR: stressed by repeated chasing, crowding or draining the tank 82. Husbandry disturbance with no effect at 25 kg/m3, positive effect at 15 and 35 kg/m3, probably due to suppressing direct aggression 58. Stressed by confinement – more so if subordinate 83. Stressed by unpredictable chronic events (chasing, netting, sudden temperature increase or decrease, noise, darkness+flash light, hypoxia, emptying the tank) 84. SMOLTS: cages: stressed by infrasound and surface disturbance 41. Increased jumping behaviour after cage submergence could be used as a stress-free delousing method from sea lice when jumping individuals break water surface with floating chemical therapeutant infused in oil 85. For stress and light → F5.

ADULTS:

  • WILD: no data found yet.
  • FARM: after smoltification, transport to sea by trucks or wellboats 9 3 12. Stressed by transport, especially loading (reducing water level, crowding, pumping) 78. Stressed by crowding and confinement 79. Occasional submergence of cages may counteract detrimental surface conditions (low oxygen levels, storms, ice, algal bloom, sea lice larvae) 11. Acoustic delicing was effective and stressless 80 and is potentially less stressful than other methods, which involve removal from water and handling. For slaughter, crowded in cages, pumped, and slaughtered on site or transported to slaughtering plant 9 81 by wellboat 81. For stress and a) aggregation → F6, b) cover → F3.
  • LAB: no data found yet.

SPAWNERS:

  • WILD: no data found yet.
  • FARM: no data found yet.
  • LAB: no data found yet.

9  Malformations

Deformities that – in contrast to diseases – are commonly irreversible may indicate sub-optimal rearing conditions (e.g., mechanical stress during hatching and rearing, environmental factors unless mentioned in crit. 3, aquatic pollutants, nutritional deficiencies) or a general incompatibility of the species with being farmed.

What is the probability of the species being malformed rarely?

It is low for minimal farming conditions, as malformation rates exceed 10%. It is medium for high-standard farming conditions, as some malformations result from conditions that may be changed (handling, heritability). Our conclusion is based on a medium amount of evidence, as improvement of the situation by adjusting conditions needs more proof.

Likelihoodscore-li
Potentialscore-po
Certaintyscore-ce

Eggs:

  • WILD: no data found yet.
  • FARM: fragile at 8-220 degree days during which handling may have repercussions 3.
  • LAB: no data found yet.

ALEVINS and FRY:

  • WILD: no data found yet.
  • FARM: no data found yet.
  • LAB: no data found yet.

PARR and SMOLTS:

  • WILD: PARR: higher frequency of otoliths containing vaterite and therefore impairing hearing in hatchery-reared than wild-caught IND (41% versus 10%) 86.
  • FARM: vertebral deformities in 2.3-21.5% coinciding with reduced growth and probably due to heritability 87. Skeletal deformities in 12% of which some do not progress after seawater transfer but instead transform from fused vertebrae into one non-deformed vertebra 88.
  • LAB: no data found yet.

ADULTS:

  • WILD: no data found yet.
  • FARM: → PARR and SMOLTS.
  • LAB: no data found yet.

GRILSE and KELTS:

  • WILD: vertebral deformities in 43% – mostly minor deviations of vertebra no 2 (compared to more severe deformities in farms) as well as fused vertebrae resulting in more stable large vertebra 44.
  • FARM: no data found yet.
  • LAB: no data found yet.

10  Slaughter

The cornerstone for a humane treatment is that slaughter a) immediately follows stunning (i.e., while the individual is unconscious), b) happens according to a clear and reproducible set of instructions verified under farming conditions, and c) avoids pain, suffering, and distress.

What is the probability of the species being slaughtered according to a humane slaughter protocol?

It is low for minimal farming conditions. It is high for high-standard farming conditions, as percussive stunning or electrical stunning, each followed by exsanguination, induce unconsciousness fast, kill while still unconscious, and are verified for the farming context. Our conclusions are based on a medium amount of evidence, as a reproducible set of rules for electrical stunning is missing.

Likelihoodscore-li
Potentialscore-po
Certaintyscore-ce

Eggs: does not apply.

ALEVINS and FRY: does not apply.

PARR and SMOLTS:

  • WILD: does not apply.
  • FARM: common slaughter method: asphyxia in air, carbon dioxide, hypothermia in ice slurry, each followed by exsanguination 81. Higher plasma cortisol levels with live chilling than control 79. High-standard slaughter method: percussive stunning 9 with a non-penetrating bolt 12 followed by exsanguination 81 12 and immersion in ice water 9, electrical stunning followed by exsanguination 81 12.
  • LAB: shorter time to loss of visual evoked response with percussive stunning or spiking (0-1 min) than with exsanguination by gill-cutting (2.5-7.5 min) or carbon dioxide narcosis (3-9 min), also vigorous movements and escape attempts with carbon dioxide 89.

ADULTS:

  • WILD: does not apply.
  • FARM: → PARR and SMOLTS.
  • LAB: no data found yet.

SPAWNERS:

  • WILD: does not apply.
  • FARM: females slaughtered after one spawning, males may be used more often 3. Isoeugenol followed by exsanguination 81.
  • LAB: no data found yet.

Side note: Domestication

Teletchea and Fontaine introduced 5 domestication levels illustrating how far species are from having their life cycle closed in captivity without wild input, how long they have been reared in captivity, and whether breeding programmes are in place.

What is the species’ domestication level?

DOMESTICATION LEVEL 5 90, fully domesticated. Cultured since 19th century 9.

Side note: Forage fish in the feed

450-1,000 milliard wild-caught fishes end up being processed into fish meal and fish oil each year which contributes to overfishing and represents enormous suffering. There is a broad range of feeding types within species reared in captivity.

To what degree may fish meal and fish oil based on forage fish be replaced by non-forage fishery components (e.g., poultry blood meal) or sustainable sources (e.g., soybean cake)?

All age classes:

  • WILD: carnivorous 91 92 93.
  • FARM: no data found yet.
  • LAB: SMOLTS: fish oil may be partly* replaced by sustainable sources 94. Fish meal may be partly* replaced by sustainable sources parallel to fish oil being mostly* replaced 95.

* partly = <51% – mostly = 51-99% – completely = 100%

Side note: Commercial relevance

How much is this species farmed annually?

Glossary

ADULTS = mature individuals
ALEVINS = larvae until the end of yolk sac absorption
ANADROMOUS = migrating from the sea into fresh water to spawn
DOMESTICATION LEVEL 5 = selective breeding programmes are used focusing on specific goals 90
FARM = setting in farming environment or under conditions simulating farming environment in terms of size of facility or number of individuals
FRY = larvae from external feeding on
GRILSE = adults returning from sea to home river to spawn
IND = individuals
JUVENILES = fully developed but immature individuals
KELTS = adults surviving spawning
LAB = setting in laboratory environment
LARVAE = hatching to mouth opening
PARR = juvenile stage in rivers
PELAGIC = living independent of bottom and shore of a body of water
PHOTOPERIOD = duration of daylight
RAS = Recirculating Aquaculture System - almost completely closed system using filters to clean and recirculate water with the aim of reducing water input and with the advantage of enabling close control of environmental parameters to maintain high water quality
SMOLTS = juvenile stage migrating to the sea
SPAWNERS = adults during the spawning season; in farms: adults that are kept as broodstock
WILD = setting in the wild

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