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)
Acipenser ruthenus is the smallest of the sturgeon family. Its current populations are considered vulnerable, majorly due to overfishing and river disruption, and differ from the original in size and biology. Although there are farms rearing this species (many of them for repopulation purposes), it is farmed majorly interbred with Huso huso as 'bester'. There is lack of knowledge on its biology in the wild as well as under farming environment, where aspects such as aggregation, aggression, stress, and malformation rate remain undisclosed. A functional stunning and slaughter protocol remains to be established. Further research directed specifically to this species should be conducted to improve its present and prospective welfare state under farming conditions.
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 farming conditions. It is medium for high-standard farming conditions. Our conclusion is based on a medium amount of evidence.
LARVAE: WILD: no data found yet. FARM: rectangular troughs: 100 L 1. For sturgeons in general, circular tanks: 2-4 m2 2; ponds: 1-4 ha 2. Further research needed to determine whether this applies to A. ruthenus as well.
JUVENILES: WILD: no data found yet. FARM: tanks: 4 m2 (2 x 2 m) 2 3 4; ponds: 1-100 ha 2 3 4. For sturgeons in general, cages: 20-100 m2 (15-20 m2 for overwintering) 2. Further research needed to determine whether this applies to A. ruthenus as well.
ADULTS: WILD: no data found yet. FARM: ➝ JUVENILES.
SPAWNERS: WILD: no data found yet. FARM: maturation tanks: 4 m2 5. For sturgeons in general, pre-spawn holding in "Kazansky" type earthen ponds: 120-130 m 2 or "Kurinsky" type earthen ponds: 30-60 x 12 m 2; long-term holding in concrete tanks: 30-50 m2 2 or cages: 20-100 m2 2; overwintering of breeders in plastic and concrete tanks: >40 m3 2 or "Kurinsky" type concrete ponds: 105 x 17 m or 1,000-4,000 ha separated into different compartments 2. Further research needed to determine whether this applies to A. ruthenus 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.
LARVAE: WILD: no data found yet. FARM: troughs: 30 cm 6. For sturgeons in general, circular tanks: 1 m 2; rearing tanks or trays: 20 cm 2. Further research needed to determine whether this applies to A. ruthenus as well.
ADULTS: ➝ JUVENILES.
SPAWNERS: WILD: 1-14 m 8 9. FARM: maturation tanks: 0.4 m 5. For sturgeons in general, pre-spawn holding in "Kazansky" type earthen ponds: 0.5-2.5 m 2 or "Kurinsky" type earthen ponds: 1.5-2.5 m 2; long-term holding in concrete tanks: 2 m 2 or cages: 3-3.5 m 2; overwintering of breeders in plastic and concrete tanks: >1.5 m 2. Further research needed to determine whether this applies to A. ruthenus 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 farming conditions. It is medium for high-standard farming conditions. Our conclusion is based on a medium amount of evidence.
JUVENILES: WILD: rivers 11, may migrate further downstream after the end of larval stages 7. FARM: reared in freshwater tanks or ponds 3 4. Dark background of tanks reduces stress responses and improves growth 12.
ADULTS: WILD: rivers 11. FARM: ➝ JUVENILES.
SPAWNERS: WILD: some populations resident, others may migrate <100-322 km 7 13 at a speed of ca 6.2 km/day 7. FARM: kept in tanks 5. Stressed by long PHOTOPERIOD under red light 14. For sturgeons in general, "Kazansky" or "Kurinsky" type earthen ponds simulate spawning reaches of rivers 2. Further research needed to determine whether this applies to A. ruthenus as well.
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 3-6, females at 4-8 years old 9. May spawn yearly or skip seasons 11. Spawning takes place in the riverbed or flooded plains 9 where adhesive eggs are laid 2 from late spring to autumn 7. FARM: temperature manipulation 2, hormonal induction of spawning 15 16 17. Stripping or highly invasive surgical methods are applied for egg collection 2 18 and maturity assessment, but less invasive ultrasound technique is available 2. Hermaphrodites and self-fertilisation occur 15.
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. It is medium for high-standard farming conditions. Our conclusion is based on a medium amount of evidence.
JUVENILES: WILD: resident populations live in aggregations of undescribed size 19. FARM: cages: 5 IND/m2 4; ponds: 0.01 kg/m2 (large ponds, extensive culture) to 20-40 kg/m2 (small ponds, intensive culture) 4.
ADULTS: ➝ JUVENILES.
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 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.
LARVAE: WILD: most sturgeons use pebbles and stones for concealment 22. Further research needed to determine whether this applies to A. ruthenus as well. FARM: usually reared in plastic tanks 1 or earthen ponds 2, where the addition of suitable substrate is possible 23.
ADULTS: ➝ JUVENILES.
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 medium amount of evidence.
Eggs: low hatching success if stored >15 ºC, best at 7-11 ºC 25.
LARVAE: no data found yet.
JUVENILES: acute stress effects of air exposure, water level reduction, and hypoxia reduced by vitamin C and E supplementation 26. For stress and tank background ➝ crit. 3.
ADULTS: no data found yet.
SPAWNERS: for stress and PHOTOPERIOD ➝ crit. 3.
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 medium amount of evidence.
LARVAE: malformations in body shape, external and internal organs, tissue structure, as well as functional and mechanical abnormalities may arise generally in sturgeons, with unknown incidence 2. Ploidy abnormalities following gynogenesis, with hatching rates of 0-50% and survival rates at day 7 of <5% 27. Thyamine administration to spawners increases larval performance and survival with no effect on parents 28.
JUVENILES: malformations of the olfactory organs, eyes, pectoral fins, and opercula, as well as phenodeviations may occur, with variable incidence and dependent on incorrect water temperatures in early stages 2 .
ADULTS: ➝ JUVENILES.
SPAWNERS: ➝ JUVENILES.
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 low amount of evidence.
Common slaughter method: for the related A. baerii, hypothermia by immersion in ice-water slurry 29. Further research needed to determine whether this applies to A. ruthenus as well. High-standard slaughter method: percussive stunning through manual spiking or percussive gun performed by experienced staff, followed by bleeding 21.
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 30, 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 8 9 31. FARM: fish meal may be partly* replaced by non-forage fishery components 32. It is possible for sturgeon farms to produce live feeds for their reared fish 2.
*partly = <51% – mostly = 51-99% – completely = 100%
DOMESTICATION LEVEL 4 = entire life cycle closed in captivity without wild inputs 30
FARM = setting in farming environment or under conditions simulating farming environment in terms of size of facility or number of individuals
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
PHOTOPERIOD = duration of daylight
POTAMODROMOUS = migrating within fresh water
SPAWNERS = adults during the spawning season; in farms: adults that are kept as broodstock
WILD = setting in the wild
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