Version: B | 1.4 (2022-07-29)
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)
Ctenopharyngodon idella is a native Chinese freshwater fish with a widespread distribution and considered one of the four Chinese major carps (among Hypophthalmichthys molitrix, H. nobilis, and Mylopharyngodon piceus). This species has been introduced into more than 50 countries throughout the world for aquatic weed control and aquaculture. In some countries, the Grass carp is an integral part of fish culture and forms an important source of protein for human consumption. Due to its success it is the third most commonly cultured species in the world. However, further research is needed on current farming conditions relating to reproduction without manipulation, aggregation, aggression, stress, and the current harvesting practices. Carp welfare can be improved using extensive culture systems promoting a natural habitat and behaviour 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?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: no data found yet. FARM: intensive conditions: raceways: 0.8 m 1; extensive conditions: ponds: 0.1-0.2 ha 1.
JUVENILES: WILD: home range <20 m 2 3. FARM: tanks: 122 cm diameter 4; ponds: 0.2-0.3 ha 1; cages: China: 60 m2 1.
ADULTS: ➝ JUVENILES.
SPAWNERS: WILD: no data found yet. FARM: tanks: 1.83 m diameter 5; raceways: 6-10 m 1.
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 low for minimal farming conditions. It is medium for high-standard farming conditions. Our conclusion is based on a medium amount of evidence.
LARVAE: WILD: remain in fresh water 6. FARM: fresh water 1. For details of holding systems ➝ crit. 1 and 2.
JUVENILES: WILD: may migrate upstream or downstream up to 1,700 km 10 6 1 7. High dispersion 11. Larger individuals move greater distances 12 3. FARM: ➝ LARVAE.
ADULTS: ➝ JUVENILES.
SPAWNERS: WILD: spawning migration upstream to reach grounds with strong current 6 1 13. FARM: ➝ LARVAE.
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 theses circumstances?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.
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.
LARVAE and FRY: WILD: no data found yet. FARM: intensive conditions: 1.2-1.5 million IND/ha 17 1; ponds for FRY: 200-250 IND/m² 18 1.
JUVENILES: WILD: shoaling 19. FARM: China: semi-intensive to intensive polyculture: ponds: 1,000-3,000 kg/ha, cages: 30-50 kg/m³ 1. Other countries: ponds: 1.5-3 IND/m², cages: 20-30 IND/m³ 1.
ADULTS: ➝ JUVENILES.
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 no findings for minimal and high-standard farming conditions.
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 low amount of evidence.
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 low 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.
LARVAE: late or non-inflated swim bladder and lower survival at 20 °C compared to higher temperatures 29.
JUVENILES: malformations of the caudal fin due to deficiently formulated diets 30 and of the vertebral column due to diets deficient in essential fatty acids 31 and vitamin E 32.
ADULTS: ➝ 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 medium for high-standard farming conditions. Our conclusion is based on a medium amount of evidence.
Common slaughter method: for the related Cyprinus carpio, 85% are sold alive, of the 15% processed in plants 33, the common methods are a) asphyxia (followed by evisceration 33 or percussive killing 34), b) percussive stunning (followed by evisceration 33 35, gill cut or destruction of the heart 35), and c) electrical stunning (followed by evisceration 33 35, gill cut or destruction of the heart 35). Further research needed to determine whether this applies to C. idella as well. High-standard slaughter method: indications that stunning in ice slurry is beneficial for flesh quality 36. Further research needed to confirm for farming conditions. For Hypophthalmichthys molitrix, another Chinese major carp, percussive stunning (one or two blows on the head with a wooden club) followed by scaling, gutting, and filleting is less stressful than immersion in ice or gill cutting followed by the same slaughter procedures 37 38. For C. carpio, electrical plus percussive stunning (followed by evisceration, gill cut or destruction of the heart) 35 or immersion in clove oil (followed by percussive killing 34). Further research needed for a specific protocol and to determine whether this applies to C. idella 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 39, 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: herbivorous 40 23. FARM: fish meal and fish oil my be partly* 17 27 41 or completely* replaced by non-forage fishery components 42. Further research needed to replicate complete replacement.
*partly = <51% – mostly = 51-99% – completely = 100%
DOMESTICATION LEVEL 5 = selective breeding programmes are used focusing on specific goals 39
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
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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