Version: B | 1.2 (2022-07-20)
Please note: This part of the profile is currently being revised.
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
FishEthoScore = Sum of criteria scoring "High" (max. 10)
Thymallus thymallus is reared for re-stocking and for feeding purposes. It is a highly appreciated species for sports fishing in northern Europe, where several initiatives have been undertaken for conservation of endangered populations. Its breeding in aquaculture relies mostly on wild parents, and many aspects of its rearing remain undisclosed. In addition, several welfare issues are probably not addressed so further research should focus mainly on substrate needs and stress effects of farming, spatial needs, reproduction without manipulation, aggregation, aggression, territoriality, and humane slaughtering.
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?It is low for minimal and high-standard farming conditions. Our conclusion is based on a medium amount of evidence.
ALEVINS: WILD: remain in the same area 1 2, avoid downstream drift 3. FARM: hatchery tanks: 1m2 4.
JUVENILES: WILD: no data found yet. FARM: rearing tanks: 16 m2 (4x4 m) 5.
ADULTS: WILD: 18-34 m 6. FARM: ➝ JUVENILES
SPAWNERS: WILD: pre-spawning: 10-950 m 7, spawning: 70-5,000 m 8 9, post-spawning: 66-144 m 9. FARM: concrete flow-through tanks 6-250 m2 (Mikolajczyk 2008)
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. It is high for high-standard farming conditions. Our conclusion is based on a medium amount of evidence.
Some species undergo seasonal changes of environments for different purposes (feeding, spawning, etc.) and with them, environmental parameters (photoperiod, temperature, salinity) may change, too. What is the probability of providing farming conditions that are compatible with the migrating or habitat-changing behaviour of the species?It is high for minimal and high-standard farming conditions. Our conclusion is based on a low amount of evidence.
ALEVINS: WILD: non-migratory, inhabiting rivers with fast moving water 14 6 15. FARM: freshwater tanks 4. For details on rearing systems ➝ crit. 1 and 2.
JUVENILES: WILD: non-migratory, inhabiting rivers with fast moving water 11 14. FARM: freshwater tanks 5. For details on rearing systems ➝ crit. 1 and 2.
ADULTS: WILD: non-migratory, inhabiting rivers with fast moving water 13 14. FARM: freshwater tanks 5. For details on rearing systems ➝ crit. 1 and 2.
SPAWNERS: WILD: may perform considerable displacements within freshwater systems 7 8 9. FARM: freshwater tanks or river-like sytems (Mikolajczyk 2008). For details on rearing systems ➝ crit. 1 and 2.
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?It is low for minimal and high-standard farming conditions. Our conclusion is based on a medium amount of evidence.
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 high for minimal and high-standard farming conditions. Our conclusion is based on a medium amount of evidence.
ALEVINS: WILD: shoal 1 12 15 6. FARM: rearing density: 4-50 larvae/L 19 20.
JUVENILES: WILD: shoal in nature 21. FARM: up to 50 kg/m3 did not decrease growth or increase mortality 5.
ADULTS: ➝ JUVENILES
SPAWNERS: WILD: form spawning aggregations 22 9. FARM: All or at least some parents in farms are wild types 4 5 18. All-female maturation tanks: 3.2-7 ind/m2; mixed-sex tanks: 0.5-2.6 ind/m2 (Mikolajczyk 2008).
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 and high-standard farming conditions. Our conclusion is based on a low amount of evidence.
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). What is the probability of providing the species' substrate and shelter needs in captivity?It is low for minimal farming conditions. It is medium for high-standard farming conditions. Our conclusion is based on a medium amount of evidence.
Eggs: WILD: adhesive 14, buried in the substrate 10. FARM: barren tanks or bottles 4 5.
ALEVINS: WILD: use substrate, prefer silt, sand, gravel 2 23 6 or pebbles 15. FARM: Ponds of Salvelinus alpinus and S. fontinalis usually have stones, pebbles and gravel as substrate (pers. obs). Further research needed to determine whether this applies to T. thymallus as well.
JUVENILES: WILD: use substrate, prefer pebbles and boulders 2 23. FARM: Ponds of Salvelinus alpinus and S. fontinalis usually have stones, pebbles and gravel as substrate (pers. obs). Further research needed to determine whether this applies to T. thymallus as well.
ADULTS: WILD: use substrate outside spawning 2 23. FARM: ➝ JUVENILES.
SPAWNERS: Use gravel 16, pebbles and stones as spawning substrate 16 7. May spawn in areas with branches and tree roots 16. FARM: maturation ponds of Salvelinus alpinus and S. fontinalis usually have stones, pebbles and gravel as substrate (pers. obs). Further research needed to determine whether this applies to T. thymallus as well.
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?There are unclear findings for minimal and high-standard farming conditions. Our conclusion is based on a low amount of evidence.
ALEVINS: no data found yet.
JUVENILES: no data found yet.
ADULTS: no data found yet.
SPAWNERS: very sensitive when spawning 17.
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?There are unclear findings for minimal farming conditions. It is medium for high-standard farming conditions. Our conclusion is based on a medium amount of evidence.
Fry: WILD: NO DATA FOUND YET. FARM: 0.1% 20.
Juveniles: WILD: NO DATA FOUND YET. FARM: When fed with live zooplankton or formulated dry food with zooplankton (DFZO): 0.1% 20. When fed with commercial dry food for salmonids, 75% develop bent tails and enlarged abdomen 20. These malformations are reversible upon feeding back with live zooplankton or DFZO 20.
Adults: WILD, FARM: NO DATA FOUND YET. All or at least some parents in farms are wild types 4 5 18.
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 medium for high-standard farming conditions. Our conclusion is based on a low amount of evidence.
Common slaughter method: for the related O. kisutch, anaesthesia with high CO2 or iced water 24, then bled by cutting gill arches and immersing in iced water 24 25. High-standard slaughter method: for O. mykiss, indications that electrical stunning before killing by chilling or bleeding is most effective 26 27 28 29. For S. salar, electrical and percussive stunning and killing by bleeding 30 31 32 33. For S. trutta, electrical stunning immediately followed by ice-water slurry 34. Further research needed whether this applies to T. thymallus as well.
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 3 35, level 5 being fully domesticated.
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 1 36 (except for omnivorous FRY stage 1 37). FARM: Replacement of fish meal and fish oil not reported in literature.
ALEVINS = larvae until the end of yolk sac absorption, for details ➝ Findings 10.1 Ontogenetic development
DOMESTICATION LEVEL 3 = entire life cycle closed in captivity with wild inputs 35
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, for details ➝ Findings 10.1 Ontogenetic development
JUVENILES = fully developed but immature individuals, for details ➝ Findings 10.1 Ontogenetic development
SPAWNERS = adults during the spawning season; in farms: adults that are kept as broodstock
WILD = setting in the wild
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25 LocalCoho Farms. 2021. Personal communication.
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