Version: B | 1.1 (2022-07-20)
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)
A variety of life-history strategies are known for Salmo trutta. This enhances the adaptability of the species to different environments and explains the success of the species' worldwide introduction. S. trutta populations can be strictly resident or anadromous, but often populations are partially anadromous, where a fraction of the populations migrate to the sea and the other fraction remains resident. The S. trutta production is insignificant compared to other Salmonidae; generally, production is destined for restocking, recreational fishing, and local consumption (mainly a niche market). In general, there is limited information on current farming conditions making it difficult to assess this species' potential when cultured in captivity. However, some biological aspects such as substrate needs and reproduction without manipulation can be considered welfare limitations to keep this species in captivity. To bridge the lack of information on welfare improvement in this species, the available information in related species such as S. salar may be a good starting point, but needs further research for validation.
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 no findings for minimal and high-standard farming conditions.
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?There are unclear findings for minimal and high-standard farming conditions. Our conclusion is based on a low 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?There are unclear findings for minimal and high-standard farming conditions. Our conclusion is based on a low amount of evidence.
Eggs: WILD: no data found yet. FARM: optimal temperature for incubation: 8 °C (range 4-12 °C) 1.
FRY: WILD: Lake trout: migration from the coastal nurseries to the rivers/lakes 3. Optimal temperature: 14 °C (range 12-16 °C). Sea trout: close to coast 3. Tolerate temperatures between 1-27 °C, but only grow when temperatures >4 °C 1. FARM: temperature: Lake trout: 10 °C, Sea trout: <12 °C 1. For details of holding systems ➝ crit. 2.
JUVENILES: WILD: Sea and Lake trout forage in pelagic and littoral habitats, Sea trout mainly close to coast, not very far from estuary of natural river 3. Optimal temperature: 14 °C (range 12-16 °C). Tolerate temperatures between 1-27 °C, but only grow when temperatures >4 °C 1. FARM: ➝ FRY.
ADULTS: WILD: ➝ JUVENILES. FARM: ➝ FRY.
SPAWNERS: spawning in rivers and streams 3. FARM: for details of holding systems ➝ crit. 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 high 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?There are unclear findings for minimal and high-standard farming conditions. Our conclusion is based on a low amount of evidence.
FRY: WILD: no data found yet. FARM: <15 kg/m³ 1.
JUVENILES: WILD and FARM: no data found yet.
ADULTS: WILD and FARM: no data found yet.
SPAWNERS: WILD and FARM: no data found yet.
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?There are unclear findings 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.
FINGERLINGS: WILD: usually found on stone, gravel, sand, silt, and mud bottoms 6 8. FARM: grown in earthen ponds 9. LAB: structural enrichment in the hatchery rearing environment improved performance in natural environment after release 10 11.
ADULTS: ➝ FINGERLINGS.
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. Our conclusion is based on a high amount of evidence.
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 no findings for minimal and high-standard farming conditions.
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. Our conclusion is based on a medium amount of evidence.
Common slaughter method: for the related O. kisutch, anaesthesia with high CO2 or iced water 16, then bled by cutting gill arches and immersing in iced water 16 17. High-standard slaughter method: electrical stunning immediately followed by ice-water slurry 9. For the related S. salar 18 19 and Oncorhynchus mykiss 20 21, humane slaughter protocol available. Further research needed to determine whether these apply to S. trutta 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 4 22, 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)?
* partly = <51% – mostly = 51-99% – completely = 100%
ALEVINS = larvae until the end of yolk sac absorption, for details ➝ Findings 10.1 Ontogenetic development
ANADROMOUS = migrating from the sea into fresh water to spawn
DOMESTICATION LEVEL 4 = entire life cycle closed in captivity without wild inputs 22
FARM = setting in farming environment or under conditions simulating farming environment in terms of size of facility or number of individuals
FINGERLINGS = early juveniles with fully developed scales and working fins, the size of a human finger; for details ➝ Findings 10.1 Ontogentic development
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
LAB = setting in laboratory environment
SPAWNERS = adults during the spawning season; in farms: adults that are kept as broodstock
WILD = setting in the wild
2 Rikardsen, Audun H., Ola H. Diserud, J. Malcolm Elliott, J. Brian Dempson, Johannes Sturlaugsson, and Arne J. Jensen. 2007. The marine temperature and depth preferences of Arctic charr (Salvelinus alpinus) and sea trout (Salmo trutta), as recorded by data storage tags. Fisheries Oceanography 16: 436–447. https://doi.org/10.1111/j.1365-2419.2007.00445.x.
3 Elliott, J. M. 1994. Biology and Ecology of the Brown Trout and Sea Trout. In Oxford Series in Ecology and Evolution, 1–283. Oxford University Press.
4 Lahti, Katriina, Anssi Laurila, Katja Enberg, and Jorma Piironen. 2001. Variation in aggressive behaviour and growth rate between populations and migratory forms in the brown trout, Salmo trutta. Animal Behaviour 62: 935–944. https://doi.org/10.1006/anbe.2001.1821.
5 Kristensen, E. A., and G. P. Closs. 2008. Variation in growth and aggression of juvenile brown trout (Salmo trutta) from upstream and downstream reaches of the same river. Ecology of Freshwater Fish 17: 130–135. https://doi.org/10.1111/j.1600-0633.2007.00266.x.
6 Heggenes, J., J. L. Baglinière, and R. A. Cunjak. 1999. Spatial niche variability for young Atlantic salmon (Salmo salar) and brown trout (S. trutta) in heterogeneous streams. Ecology of Freshwater Fish 8: 1–21. https://doi.org/10.1111/j.1600-0633.1999.tb00048.x.
7 Schneider, Bruno. 2000. Spawning Microhabitat Selection by Brown Trout in the Linthkanal, a Mid-Sized River. Journal of Freshwater Ecology 15: 181–187. https://doi.org/10.1080/02705060.2000.9663735.
8 Ayllón, D., A. Almodóvar, G. G. Nicola, and B. Elvira. 2010. Ontogenetic and spatial variations in brown trout habitat selection. Ecology of Freshwater Fish 19: 420–432. https://doi.org/10.1111/j.1600-0633.2010.00426.x.
9 Castanheira, Maria Filipa. 2017. Personal communication.
10 Härkönen, Laura, Pekka Hyvärinen, Juuso Paappanen, and Anssi Vainikka. 2014. Explorative behavior increases vulnerability to angling in hatchery-reared brown trout (Salmo trutta). Canadian Journal of Fisheries and Aquatic Sciences 71: 1900–1909. https://doi.org/10.1139/cjfas-2014-0221.
11 NOT FOUND
12 Brabrand, A., A.G. Koestler, and R. Borgstrom. 2002. Lake spawning of brown trout related to groundwater influx. Journal of Fish Biology 60: 751–763.
13 Pickering, A. D., and A. Stewart. 1984. Acclimation of the interrenal tissue of the brown trout, Salmo trutta L., to chronic crowding stress. Journal of Fish Biology 24: 731–740. https://doi.org/10.1111/j.1095-8649.1984.tb04844.x.
14 Pickering, A. D. 1989. Environmental stress and the survival of brown trout, Salmo trutta. Freshwater Biology 21: 47–55. https://doi.org/10.1111/j.1365-2427.1989.tb01347.x.
15 Pickering, A. D., R. Griffiths, and T. G. Pottinger. 1987. A comparison of the effects of overhead cover on the growth, survival and haematology of juvenile Atlantic salmon, Salmo salar L., brown trout, Salmo trutta L., and rainbow trout, Salmo gairdneri Richardson. Aquaculture 66: 109–124. https://doi.org/10.1016/0044-8486(87)90226-2.
16 Fairgrieve, W. 2009. Cultured Aquatic Species Information Programme. Oncorhynchus kisutch. Rome: FAO Fisheries and Aquaculture Department.
17 LocalCoho Farms. 2021. Personal communication.
18 European Food Safety Authority (EFSA). 2009. Species-specific welfare aspects of the main systems of stunning and killing of farmed Atlantic Salmon. EFSA Journal 7: 1–77. https://doi.org/10.2903/j.efsa.2009.1011.
19 Lambooij, E., E. Grimsbø, J. W. van de Vis, H. G. M. Reimert, R. Nortvedt, and B. Roth. 2010. Percussion and electrical stunning of Atlantic salmon (Salmo salar) after dewatering and subsequent effect on brain and heart activities. Aquaculture 300: 107–112. https://doi.org/10.1016/j.aquaculture.2009.12.022.
20 Lines, J. A., D. H. Robb, S. C. Kestin, S. C. Crook, and T. Benson. 2003. Electric stunning: a humane slaughter method for trout. Aquacultural Engineering 28: 141–154. https://doi.org/10.1016/S0144-8609(03)00021-9.
21 European Food Safety Authority (EFSA). 2009. Species-specific welfare aspects of the main systems of stunning and killing of farmed fish: Rainbow Trout. EFSA Journal 7: 1012. https://doi.org/10.2903/j.efsa.2009.1012.
22 Teletchea, Fabrice, and Pascal Fontaine. 2012. Levels of domestication in fish: implications for the sustainable future of aquaculture. Fish and Fisheries 15: 181–195. https://doi.org/10.1111/faf.12006.
23 Pentelow, F. T. K. 1932. The Food of the Brown Trout (Salmo trutta L.). Journal of Animal Ecology 1: 101–107. JSTOR. https://doi.org/10.2307/972.
24 Arslan, Murat, Necdet Sirkecioglu, Abdulkadir Bayir, Harun Arslan, and Mevlut Aras. 2012. The influence of substitution of dietary fish oil with different vegetable oils on performance and fatty acid composition of brown trout, Salmo trutta. Turkish Journal of Fisheries and Aquatic Sciences 12: 575–583.
25 Oliva-Teles, Aires, Paula Enes, and Helena Peres. 2015. Replacing fishmeal and fish oil in industrial aquafeeds for carnivorous species. Feed and Feeding Practices in Aquaculture. Woodhead Publishing Series in Food Science, Technology and Nutrition: 203–233.