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)
Huso huso is a long-lived and late maturing species endemic to the Ponto-Caspian Sea region, which includes the Caspian Sea, the Sea of Azov, and the Black Sea. It is also present in the Adriatic Sea, although rare, and is critically endangered due to the construction of hydroelectric dams and the effects of human activities. It spawns in the lower Danube and a few other rivers in Kazakhstan, Azerbaijan, Iran, and Turkey. H. huso is highly valued for its caviar and meat and is intensively farmed. However, there are many knowledge gaps about its natural habitat and behaviour, such as its home range and its social and reproductive behaviour. Currently, the depth and migratory needs of H. huso are not met in farming conditions, the reproduction is highly invasive, and a humane slaughtering method needs to be researched and implemented. Further research in these areas would improve the welfare of the species.
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. Our conclusion is based on a medium amount of evidence.
JUVENILES: WILD: no data found yet. FARM: fibreglass tanks: 4 m2 (2 x 2 m) 7 8, 1 m2 (1 x 1 m) 9, 2 m diameter 10 8 2; concrete tanks: 1.9-3 m diameter 11 8; coloured glass tanks: 0.4 m2 (0.9 x 0.5 m) 12; enriched earthen ponds 6: 20,000 m2 2, 43,200 m2 (180 x 240 m) 1. For sturgeons in general, cages: 20-100 m2 (15-20 m2 for overwintering), earthen ponds: 1-4 ha 13. Further research needed to determine whether this applies to H. huso as well.
SPAWNERS: WILD: no data found yet. FARM: concrete tanks 14: 36 m3 6, 200 m2 (14.3 x 14 m) 2. For sturgeons in general, pre-spawn holding in "Kazansky" type earthen ponds: 120-130 m 13 or "Kurinsky" type earthen ponds: 30-60 x 12 m 13; long-term holding in concrete tanks: 30-50 m2 13 or cages: 20-100 m2 13; overwintering of breeders in plastic and concrete tanks: >40 m3 13 or "Kurinsky" type concrete ponds: 105 x 17 m or 1,000-4,000 ha separated into different compartments 13. Further research needed to determine whether this applies to H. huso as well.
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 and high-standard farming conditions. Our conclusion is based on a medium amount of evidence.
JUVENILES: WILD: in the Danube delta: 4.5-20 m 16. FARM: fibreglass tank: 0.5 m 7 10 8, 0.6 m 9, water depth 0.3 m 7 9 2; circular tanks: water depth 0.5 m 11; glass tanks: 0.4 m 12. For sturgeons in general, ponds: 2.3-2.5 m 13; cages: 2.5-3.5 m 13. Further research needed to determine whether this applies to H. huso as well.
ADULTS: WILD: in the Caspian Sea: in winter: >30 m 17; in spring: 10-20 m 17. In the Danube delta: in summer: 12.8-19.2 m 16; in autumn: 12.5-18 m 16. FARM: concrete tanks: 1.5 m with slope 2, 0.4 m 2.
SPAWNERS: WILD: in winter: deep zones of the river 17 18; in spring: spawn in deep pebble bottoms 17. When migrating: 2.4-21.2 m 19, 1-35 m (with preference for 8-12 m for upstream migration and 9-15 m for downstream migration) 20. Spawning at 4-40 m 18, 9-22 m 21. FARM: for sturgeons in general, pre-spawn holding in "Kazansky" type earthen ponds: 0.5-2.5 m 13 or "Kurinsky" type earthen ponds: 1.5-2.5 m 13; long-term holding in concrete tanks: 2 m 13 or cages: 3-3.5 m 13; overwintering of breeders in plastic and concrete tanks: >1.5 m 13. Further research needed to determine whether this applies to H. huso as well.
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 low for minimal and high-standard farming conditions. Our conclusion is based on a medium amount of evidence.
LARVAE and FRY: WILD: lower Danube 15. Downstream migration at 60 km/day 23-18. Based on distribution, 9-15 h photoperiod. FARM: ponds: 16-24 °C 13, fresh water gradually increasing in salinity to 13 ppt at 35 days 24-13. For details of holding systems ➝ crit. 1 and 2.
JUVENILES: WILD: in shallow coastal waters 18. Live in the NW shelf of the Black Sea 25. Potential overwintering in the Lower Danube 15. Based on distribution, 9-15 h photoperiod. FARM: higher survival at 12L:12D cycle than at 0L:24D, 18L:6D, and 24L:0D, stressed by 0L:24D or 24L:0D cycles (12L:12D cycle induced less stress than other ones) 9. Blue light improved weight gain 12, red light decreased growth and increased stress 12. Tendency of increased growth and decreased stress in black tanks 12. Tanks: 10-22 °C 13. For details of holding systems ➝ crit. 1 and 2.
ADULTS: WILD: populations in Caspian Sea, Black Sea, Azov Sea, Adriatic Seas 17 18. In Caspian Sea: in summer, in SE region 17, in autumn, feeding migration to south of the Gasan-Kuli-Aster line 17. In Black Sea: return to the NW shelf after spawning in the Danube 25. Based on distribution, estimated 9-15 h PHOTOPERIOD. FARM: tanks: 12 h PHOTOPERIOD 12, 10-22 °C 13. For details of holding systems ➝ crit. 1 and 2.
SPAWNERS: WILD: populations in Volga, Dnieper 17, Danube, Ural, Kura 17 18, and other rivers 18. In Black Sea: migrate <1,700 km 26-22 27-22 into the Danube in the winter (Aug-Nov) or spring (Jan-April) 26-22 27-22 18 19 at 0-14.4 °C 19 at about 13.8-34 km/day. Winter strain: overwinters in the river 22 17 near spawning areas easily accesible in the spring 18. Based on distribution, estimated 9-15 h PHOTOPERIOD. FARM: for sturgeons in general, "Kazansky" or "Kurinsky" type earthen ponds simulate spawning reaches of rivers 13, 4-21 °C and fresh water in tanks 13, overwintering at 2-6 °C 13. Further research needed to determine whether this applies to H. huso as well. For details of holding 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.
WILD: males mature at age 12-16 and spawn every 4-7 years 18. Females mature at 16-22 years and spawn every 5-7 years 18. Spawn in spring with water temperature of 9-17 ºC 28-18, or 13-15 ºC 21. Spawning requires a strong river flow (25,000 m3/s) for 15-20 days 29-17. FARM: males mature at 5-8 years, females at 9-12 years 30-13. Kept at constant high temperatures (15-22 °C) year round (except overwintering period) to decrease generation intervals, i.e. time between spawning 13. Females fail to reach sexual maturity naturally under farm conditions 31-32, so breeders are taken from the wild 13. Biopsy or minimally invasive laparoscopy to identify sex and assess maturity 2, after 3-4 years of age also non-invasively via ultrasonography 33-2 13. Stressed by handling for sex identification (endoscopy) 8. Ovulation and spermiation induced by hormonal injection 34 35 36 37. Collection of sperm and eggs for fertilisation 35 36 with catheter 37, stripping 38 13, laparotomy 13, minimally invasive surgery 39 – under anaesthesia 13 39 – or after killing 2.
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 and high-standard farming conditions. Our conclusion is based on a medium amount of evidence.
LARVAE and FRY: WILD: no data found yet. FARM: concrete tanks: 24,000 IND/m3 1, 3,600 IND/m3 4, 5,000-10,000 IND/m3 or 1,000-2,000 IND/m2 13; fibreglass tanks: 942 IND/m3 5, 5,000-10,000 IND/m3 or 1,000-2,000 IND/m2 13; enriched earthen ponds: 1.3 IND/m2 1, 9 IND/m2 13.
JUVENILES: WILD: solitary 40. FARM: decreasing growth 7 8 41 and increasing stress with increasing density from 1 kg/m2 to 8 kg/m2 7 or from 50 IND/m3 to 125 IND/m3 41. Densities of 7 kg/m2 8 11 and 75-125 IND/m3 41 increase stress during husbandry practices compared to lower densities. Enriched earthen ponds: 1.3 IND/m2 1.
ADULTS: WILD: solitary, except in winter 16. FARM: no data found yet.
SPAWNERS: WILD: migrate in large shoals 42 40. FARM: tanks: 5-12 kg/m2 for junior replacement, 15-40 kg/m2 for senior replacement 13; cages: 6-9 kg/m2 for junior replacement 13, 10-30 kg/m2 for senior replacement 13, 15-20 kg/m2 during overwintering 13; ponds: 3-5 kg/m2 for junior replacement 13, 6-10 kg/m2 for senior replacement 13, 25-30 kg/m3 during overwintering 13.
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. It is medium for 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 high for high-standard farming conditions. Our conclusion is based on a medium amount of evidence.
Eggs: WILD: attached to gravel or cobble until hatching (10-14 days) 18. FARM: no data found yet.
JUVENILES: WILD: no data found yet. FARM: clay loam and cow manure in enriched earthen ponds 1. For details of holding systems ➝ crit. 1 and 2.
ADULTS: WILD: PELAGIC 18. FARM: for details of holding systems ➝ crit. 1 and 2.
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 and high-standard farming conditions. Our conclusion is based on a medium 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?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.
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: hypothermia by immersion in ice-water slurry 38. High-standard slaughter method: for Acipenser gueldenstaedtii, A. naccarii, A. ruthenus, A. stellatus, A. transmontanus, percussive stunning through manual spiking or percussive gun performed by experienced staff, followed by bleeding 45; for A. baerii, electronarcosis and percussive stunning by spiking, followed by bleeding 46. Further research needed to determine whether this applies to H. huso 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 5 , 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 clases: WILD: carnivorous 25 17 18 with focus on invertebrates in JUVENILES 18 and fishes in ADULTS 25 17 18. FARM: fish meal may be partly* replaced by sustainable components 48, fish oil completely* by 49 50, but no data found yet for ADULTS and SPAWNERS.
partly = <51% – mostly = 51-99% – completely = 100%
0L = 0h light
12D = 12 h dark
12L = 12 h light
18L = 18 h light
24D = 24 h dark
24L = 24 h light
6D = 6 h dark
ADULTS = mature individuals, for details ➝ Findings 10.1 Ontogenetic development
ANADROMOUS = migrating from the sea into fresh water to spawn
DOMESTICATION LEVEL 5 = selective breeding programmes are used focusing on specific goals 47
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
IND = individuals
JUVENILES = fully developed but immature individuals, for details ➝ Findings 10.1 Ontogenetic development
LARVAE = hatching to mouth opening, for details ➝ Findings 10.1 Ontogenetic development
PELAGIC = living independent of bottom and shore of a body of water
PHOTOPERIOD = duration of daylight
SPAWNERS = adults during the spawning season; in farms: adults that are kept as broodstock
WILD = setting in the wild
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