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Blue tilapia

Oreochromis aureus
Oreochromis aureus (Blue tilapia)
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Distribution
no distribution map available



Information

Author: Caroline Marques Maia
Version: C | 1.1 (2024-12-31)


Reviewer: Jenny Volstorf
Editor: Jenny Volstorf

Initial release: 2024-10-09
Version information:
  • Appearance: C
  • Last minor update: 2024-12-31

Cite as: »Marques Maia, Caroline. 2024. Oreochromis aureus (WelfareCheck | farm). In: fair-fish database, ed. fair-fish. World Wide Web electronic publication. Version C | 1.1. https://fair-fish-database.net.«





WelfareScore | farm

Oreochromis aureus
LiPoCe
Criteria
Home range
score-li
score-po
score-ce
Depth range
score-li
score-po
score-ce
Migration
score-li
score-po
score-ce
Reproduction
score-li
score-po
score-ce
Aggregation
score-li
score-po
score-ce
Aggression
score-li
score-po
score-ce
Substrate
score-li
score-po
score-ce
Stress
score-li
score-po
score-ce
Malformations
score-li
score-po
score-ce
Slaughter
score-li
score-po
score-ce


Legend

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

WelfareScore = Sum of criteria scoring "High" (max. 10)

score-legend
High
score-legend
Medium
score-legend
Low
score-legend
Unclear
score-legend
No findings



General remarks

Oreochromis aureus is a freshwater and tropical fish that naturally inhabits warm ponds and impoundments as well as lakes and streams of Africa and Eurasia. It is found both in open waters and among stones and vegetation, being tolerant to very brackish waters and one of the most cold-tolerant tilapia species, occurring at temperatures ranging from 8 to 30 °C. O. aureus is a filter-feeding fish, but also feeds on aquatic vegetation, invertebrates, and even FISHES, thus being an opportunistic feeder. This tilapia is already introduced around the world as a food source, for vegetation control, and as a game fish. Despite that, there are reports about adverse ecological impact after introduction.

Aiming to avoid natural spawning and because males grow better than females, manual sexing, hybridisation with O. niloticus and hormonal sex reversal have been used to produce monosex-male populations in farms. Important wild information about home range, depth range, migration distances, and aggregation densities is still missing from the literature for this species. Moreover, further research about farming conditions related to aggression, stress responses, malformations, and substrate availability is needed for a better welfare assesment for farmed O. aureus. Additionally, farming information about home range, depth range, and aggregation conditions for the early life stages is still missing as well.

Note: we used some older sources that referred to O. aureus as Tilapia nilotica123 or Tilapia aurea exul4, as was common at the time.




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 unclear for minimal and high-standard farming conditions, given we mainly found data from farms. Our conclusion is based on a low amount of evidence, as further research is needed on home range in the wild.

Likelihoodscore-li
Potentialscore-po
Certaintyscore-ce

Eggs: does not apply.

LARVAE and FRY:

  • WILD: maternally mouthbred 12356789. MOUTHBROODER females release FRY not before 10 mm TOTAL LENGTH1, stay close to schooling FRY and take up into mouth again when necessary until 5 days old 10↶11 (the latter unclear whether it is WILD or FARM12). After females are gone, no data found yet on home range.
  • FARM: are collected from female’s mouth every 14 days 13, hatch in plastic hatching jars 7. For the related O. niloticus, hatch in female’s mouth in breeding ponds (females leave when FRY reach 9-10 mm TOTAL LENGTH) 14 or are collected from female’s mouth 1514 every 5-7 days 1614, 10 days 17 to hatch in incubation jars 15 or 1-10 m3 nursery tanks 14 or 1-2 m218, 9-40 m2 (3 x 3 m, 8 x 2.5 m, 8 x 5 m) hapas in nursery ponds or directly in 100-500 m2 nursery ponds 14, 100-1,000 m219 or 200 m3 tanks 20. From incubation jars to pre-growing ponds: 30 m2 (3 x 10 m) 15. FINGERLINGS ponds: 200 m221. Pre-growing cages: 1 m2 (1 x 1 m) 22, 4 m2 (2 x 2 m) 23. Further research needed to determine whether this applies to O. aureus as well.
  • LAB: does not apply.

JUVENILES:

  • WILD: no data found yet.
  • FARM: ponds: 10,000 m224, 25,000-65,000 m225; pens in ponds: 12 m2 (4 x 3 m) 26; cages: 3 m327; tanks: 13 m327.
  • LAB: does not apply.

ADULTS:

  • WILD: no data found yet.
  • FARM: ponds: 10,000 m224, 25,000-65,000 m225.
  • LAB: does not apply.

SPAWNERS:

  • WILD: nests of 0.4 m ∅ 5, 0.9 m ∅ 1. Maternal MOUTHBROODER12356789. MOUTHBROODER females release FRY not before 10 mm TOTAL LENGTH1, stay close to schooling FRY and take up into mouth again when necessary until 5 days old 10↶11 (the latter unclear whether it is WILD or FARM12).
  • FARM: spawning fibreglass tanks: 4 m2 (2 x 2 m) 7; spawning hapas in ponds: 3.2 m2 (2.7 x 1.2 m) 6. Normal or pseudofemales: spawning ponds: 200 m228; spawning tanks: 4 m2 (2 x 2 m) 28. IND of the same species or for hybridisation with O. niloticus: concrete ponds: 3 m2 (3 x 1 m) 29.
  • LAB: does not apply.



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 in case the unclear depth range is fully used (mean 9 m), as ponds, tanks, and pens do not cover this whole range in the wild. It is high for high-standard farming conditions, as ponds are easily imaginable to cover the whole depth range in the wild that we can be certain about (<2.4 m). Our conclusion is based on a medium amount of evidence, as further research is needed on the actual depth range used.

Likelihoodscore-li
Potentialscore-po
Certaintyscore-ce

Eggs:

  • WILD: maternally mouthbred 12356789.
  • FARM: incubated in plastic hatching jars 7. For the related O. niloticus, mouthbred 14 or collected from female’s mouth 1514 every 5-7 days 1614, 10 days 17 to hatch in jars and trays 14. Further research needed to determine whether this applies to O. aureus as well.
  • LAB: does not apply.

LARVAE and FRY:

  • WILD: maternally mouthbred 12356789. After spawning, MOUTHBROODER females move to deeper waters 10↶1131↶11, unclear whether it is WILD or FARM12. FRY: rivers: 0.5-1.5 m (non-native habitat: 32) with unclear depth range use.
  • FARM: are collected from female’s mouth every 14 days 13. For the related O. niloticus, hatch in female’s mouth in breeding ponds (females leave when FRY reach 9-10 mm TOTAL LENGTH) 14 or are collected from female’s mouth 1514 every 5-7 days 1614, 10 days 17. Ponds: 0.5-1.4 m 19. Hapas in nursery ponds: 0.8-1.5 m 14, 1-2 m 18, increasing pond and hapa depth increases hatching rate and improves larval development through providing lower temperatures 14. FINGERLINGS ponds (until market size and beyond): higher growth and lower mortality at 3 m than 0.5, 1, or 2 m 21. Pre-growing cages: 1 m 22, 2 m 23. Further research needed to determine whether this applies to O. aureus as well.
  • LAB: does not apply.

JUVENILES:

  • WILD: BENTHOPELAGIC33, preferring shallow waters 34. Lakes: 0.5-1.9 m 35, lake Maryut 5 with 0.6-2.7 m 36, artificial lake of 1-1.5 m 37, average 1.4 m 38, ca 2 m max 39, average 2.6 m 40, all with unclear depth range use; rivers: caught at 0.5-2.4 m (non-native habitat: 41); Rosetta branch of Nile river: 2-4 m 42↶43, rivers: 0.5-1.5 m (non-native habitat: 32), mean 9 m (non-native habitat: 9), all with unclear depth range use.
  • FARM: ponds: 1-2 m 2425; pens in ponds: 1 m 26.
  • LAB: does not apply.

ADULTS:

  • WILD: BENTHOPELAGIC33. Lakes: 0.5-1.9 m 35, lake Maryut 5 with 0.6-2.7 m 36, artificial lake of 1-1.5 m 37, average 1.4 m 38, ca 2 m max 39, average 2.6 m 40, all with unclear depth range use; rivers: caught at 0.5-2.4 m (non-native habitat: 41); Rosetta branch of Nile river: 2-4 m 42↶43, rivers: mean 9 m (non-native habitat: 9), all with unclear depth range use.
  • FARM: ponds: 1-2 m 2425.
  • LAB: does not apply.

SPAWNERS:

  • WILD: lakes: 0.5-1.9 m 35, lake Maryut 5 with 0.6-2.7 m 36, all with unclear depth range use; rivers: mean 9 m (non-native habitat: 9) with unclear depth range use. Nesting in <2 m (mainly at 0.3-0.8 m) 34, 0.6-0.9 m 1, and in shallow lagoon habitats, but also in open-shore areas with inundated vegetation 34. Nests are holes of ≤0.5 m depth 1. Maternal MOUTHBROODER12356789. After spawning, MOUTHBROODER females swim to deeper waters 10↶1131↶11, unclear whether it is WILD or FARM12.
  • FARM: spawning fibreglass tanks: 0.5 m 7; spawning hapas in ponds: 0.4-0.8 m 6. Normal or pseudofemales: spawning ponds: 0.5-1.5 m 28. IND of the same species or for hybridisation with O. niloticus: concrete ponds: 1.2 m 29.​
  • LAB: does not apply.



3  Migration

Some species undergo seasonal changes of environments for different purposes (feeding, spawning, etc.), and to move there, they migrate for more or less extensive distances.

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, as the species undertakes more or less extensive migrations (even though of unknown distance), and we cannot be sure that providing each age class with their respective environmental conditions will satisfy their urge to migrate or whether they need to experience the transition. It is unclear for high-standard farming conditions, as we lack wild information to compare the farming conditions to. Our conclusion is based on a low amount of evidence, as further research is needed on specific migration distances in the wild.

Likelihoodscore-li
Potentialscore-po
Certaintyscore-ce

POTAMODROMOUS44.

Eggs: does not apply.

LARVAE and FRY:

  • WILD: maternally mouthbred in brackish 1453545 to saline waters 545.
  • FARM: for details of holding systems →F1 and F2.
  • LAB: no data found yet.

JUVENILES:

  • WILD: brackish water 5353940 to saline waters 5. For the related O. niloticus, mainly in inshore waters of one (brackish) lake, sometimes moving offshore 46, in other lake: mostly open water 46, probably disperse after nursery phase into open waters 47. Non-native habitat: feeding at lake edges, in lagoons in estuaries of inflowing rivers, living off-shore in lakes 48, moving between littoral with vegetation close to shore and deeper off shore with sandy or rocky bottom 49. Further research needed to determine whether this applies to O. aureus as well.
  • FARM: cages: oligohaline to mesohaline waters (with maximum salinity 15 ppt) 27. Ponds: seawater (38.8-43.7‰), but with high mortality 24. For details of holding systems →F1 and F2.
  • LAB: no data found yet.

ADULTS:

  • WILD: brackish water 45353940 to saline waters 5. For the related O. niloticus→JUVENILES. 
  • FARM: ponds: seawater (38.8-43.7‰), but with high mortality 24. For details of holding systems →F1 and F2.
  • LAB: no data found yet.

SPAWNERS:

  • WILD: maternal MOUTHBROODER in brackish 14535 to saline waters 5. Breed close to shore 1. After spawning, MOUTHBROODER females swim to deeper waters 10↶1131↶11, unclear whether it is WILD or FARM12.
  • FARM: spawning fibreglass tanks: salinity: 3-5 g/L (low-salinity underground water) 7. For details of holding systems →F1 and F2.
  • LAB: no data found yet.



4  Reproduction

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 these circumstances?

It is high for minimal and high-standard farming conditions, as natural breeding (without manipulation) with farm-reared IND is possible and verified for the farming context. Our conclusion is based on a medium amount of evidence, as further research is needed on reproduction behaviour in the wild.

Likelihoodscore-li
Potentialscore-po
Certaintyscore-ce

Eggs: does not apply.

LARVAE and FRY: does not apply.

JUVENILES: does not apply.

ADULTS: does not apply.

SPAWNERS:

  • WILD: start maturing at 3 months of age 8, non-native habitat: 1.5-2.5 years, females earlier than males 50. Spawning season: April-August 24734 (spring-early summer 34), Feb-Nov with peaks in May and Sept-Oct 51, non-native habitat: year round 5253, highest activity January-May 53 or peak in July 52. Multiple spawnings 68, asynchronously 6. Courting behaviour in the nest: male displays to female 1, lateral display by both sexes with nipping and tail-flapping 10↶1131↶11 (the latter unclear whether it is WILD or FARM12). Maternal MOUTHBROODER12356789, females take eggs in mouth after fertilisation 1, caring from eggs to FRY8: stay close to FRY and take up into mouth again when necessary until 5 days old 10↶11 (the latter unclear whether it is WILD or FARM12). For nest building →F3.
  • FARM: in Egypt, IND may be taken from the wild 5, although unclear whether this is still the case 12. Mature at 15 months 28; used for spawning at 2 years old 67; spawn February-July, with peak in April-May 28. Natural spawning 24628729. Fibreglass tanks: sex ratio: 1:3 male:female 7; hapas: sex ratio: 1:1. Normal or pseudofemales: tanks or ponds: sex ratio: 1:3 male:female 28. IND of the same species or for hybridisation with O. niloticus: ponds: sex ratio: 1:3 male:female 29.
  • LAB: maternal MOUTHBROODER54.



5  Aggregation

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, as densities in pens, cages, and tanks go beyond the smallest density in the wild (although we cannot be sure in all age classes). It is medium for high-standard farming conditions, as densities in ponds at least overlap with the density range in the wild. Our conclusion is based on a low amount of evidence, as further research is needed on densities in the wild.

Likelihoodscore-li
Potentialscore-po
Certaintyscore-ce

Eggs: does not apply.

LARVAE and FRY:

  • WILD: maternally mouthbred 12356789. MOUTHBROODER females release FRY not before 10 mm TOTAL LENGTH1, stay close to schooling FRY and take up into mouth again when necessary until 5 days old 10↶11 (the latter unclear whether it is WILD or FARM12). After females are gone, no data found yet on aggregation type.
  • FARM: are collected from female’s mouth every 14 days 13. For the related O. niloticus, hatch in female’s mouth in breeding ponds (females leave when FRY reach 9-10 mm TOTAL LENGTH) 14 or are collected from female’s mouth 1514 every 5-7 days 1614, 10 days 17. FRY: stocking in FINGERLINGS ponds: 10 IND/m214, nursery ponds: 100-200 IND/m214, 500 IND/m3 (concrete) 17, 100-1,000 IND/m219. Incubation systems: 5 IND/L, hapas in earthen ponds: 1,000-2,000 IND/m214. Higher growth in hapa nets with 250 IND/m2 than hapa nets with 1,000 IND/m2 and concrete tanks with 1,000 IND/m255. Cages: survival >75% at 1,000-3,000 IND/m3 for pre-growing IND to 2 months, decreasing survival at densities beyond that 22, 800 IND/m2 for pre-growing 2 months old IND to 5 months 22, higher growth of monosex male FINGERLINGS at 400 IND/m2 than 500 or 600 IND/m223. Further research needed to determine whether this applies to O. aureus as well.
  • LAB: no data found yet

JUVENILES:

  • WILD: schooling 33; 0-5 IND/m234.
  • FARM: ponds: 0.01 IND/m2 in a polyculture with Sparus auratus, Liza aurata, and Trachinotus ovatus of overall density of 0.05 IND/m224. Pens in ponds: 1.7 IND/m226. Cages: 33.4 IND/m327. Tanks: 26.7-35.3 IND/m327.
  • LAB: monoculture: young IND: 1.3 IND/L, old IND: 0.4 IND/L; polyculture with Cyprinus carpio: young IND: 0.5 or 0.8 IND/L of overall density of 1.3 IND/L, old IND: 0.2 or 0.3 IND/L of overall density of 0.4 IND/L 56.

ADULTS:

  • WILD: schooling 33.
  • FARM: ponds: 0.01 IND/m2 in a polyculture with S. auratus, L. aurata, and T. ovatus of overall density of 0.05 IND/m224.
  • LAB: no data found yet.

SPAWNERS:

  • WILD: males visit female schools and attempt to attract a female spawning partner 10↶1131↶11, unclear whether it is WILD or FARM12. Nests with 1 m distance from each other 5.
  • FARM: spawning fibreglass tanks: 2.8 IND/m27; spawning hapas in ponds: 3.7 IND/m26. Normal or pseudofemales: spawning ponds: 1.8-2.3 IND/m228. IND of the same species or for hybridisation with O. niloticus: concrete ponds: 4 IND/m329.
  • LAB: no data found yet.



6  Aggression

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, as the species is aggressive in almost all age classes. It is medium for high-standard farming conditions, as ways to reduce (but not avoid) aggression (polyculture) are verified for the farming context. Our conclusion is based on a medium amount of evidence, as further species-specific research is needed on LARVAE, FRY, and SPAWNERS.

Likelihoodscore-li
Potentialscore-po
Certaintyscore-ce

Eggs: does not apply.

LARVAE and FRY:

  • WILD: maternally mouthbred 12356789. MOUTHBROODER females release FRY not before 10 mm TOTAL LENGTH1, stay close to schooling FRY and take up into mouth again when necessary until 5 days old 10↶11 (the latter unclear whether it is WILD or FARM12). After females are gone, no data found yet on aggression.
  • FARM: are collected from female’s mouth every 14 days 13. For the related O. niloticus, hatch in female’s mouth in breeding ponds (females leave when FRY reach 9-10 mm TOTAL LENGTH) 14 or are collected from female’s mouth 1514 every 5-7 days 1614, 10 days 17. Leaving LARVAE to develop in breeding pond and scooping FRY may be difficult to get all IND out and because of cannibalism 57, cannibalism and predation by larger IND may be prevented by avoiding high stocking densities, by regular size grading, or by using double hapa which separates breeders from FRY14. Stocking FRY of same age prevented cannibalism 22. Further research needed to determine whether this applies to O. aureus as well.
  • LAB: no data found yet.

JUVENILES:

  • WILD: territorial 33. Non-native habitat: cannibalism of youngs 58; competition for space and food 52.
  • FARM: cages and tanks: different tilapia species including O. aureus and hybrids kept separately to avoid aggressive behaviour 27. Ponds (with or without integrated system with ducks culture): no aggression reported in polyculture with Cyprinus carpio, Hypophthalmichthys molitrix, Mugil cephalus, O. niloticus25.
  • LAB: no aggression reported in polyculture with C. carpio, better growth for both species than in monocultures 56. Less aggression and higher growth in polyculture with C. carpio at 60 O. aureus:40 C. carpio than in monocultures or in 40:60 polycultures 59. Competition (possibly with aggression) in polyculture with Micropterus salmoides, suggested to explain the reduced growth rate of M. salmoides60. Higher growth and survival rate for both species in polyculture with Mesopotamichthys sharpeyi than monocultures – possible food competition and limited aggressive interactions mentioned 61.

ADULTS:

  • WILD: →JUVENILES.
  • FARM: ponds (with or without integrated system with ducks culture): no aggression reported in polyculture with C. carpio, H. molitrix, M. cephalus, O. niloticus25.
  • LAB: less aggression and higher growth in polyculture with C. carpio at 60 O. aureus: 40 C. carpio than in monocultures or in 40:60 polyculture 59.

SPAWNERS:

  • WILD: male guards nest 4.
  • FARM: for the related O. niloticus, important to select IND of similar size, otherwise males 30-40% larger than females become very aggressive, nipping at females until the point of mortality 14. Increasing aggression with increasing density 14. Further research needed to determine whether this applies to O. aureus as well.
  • LAB: such extreme aggression and mortality in pairs of breeders in aquaria that study had to be aborted 62. Pseudofemales (hormonally sex-reversed males) more aggressive and are more dominant than females, with tendeny to increase with increasing stocking density 63.



7  Substrate

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, turbidity).

What is the probability of providing the species' substrate and shelter needs in captivity?

It is low for minimal farming conditions, as almost all age classes of the species use substrate, but pens, cages, and some tanks are devoid of it. It is medium for high-standard farming conditions given a) eggs are left in female’s mouth, b) earthen ponds for FRY to ADULTS which are not replaced by concrete bottom, and given c) natural reproduction with spawning substrate in ponds for SPAWNERS. Our conclusion is based on a low amount of evidence, as further species-specific research is needed, also to determine whether shading and aerial protection nets suffice as replacements of inundated vegetation and macrophytes.

Likelihoodscore-li
Potentialscore-po
Certaintyscore-ce

Eggs:

  • WILD: maternally mouthbred 12356789.
  • FARM: for the related O. niloticus, ponds: shading increases hatching rate through lower temperatures 14. Further research needed to determine whether this applies to O. aureus as well. For details of holding systems →F2.
  • LAB: no data found yet.

LARVAE and FRY:

  • WILD: maternally mouthbred 12356789. MOUTHBROODER females release FRY not before 10 mm TOTAL LENGTH1, stay close to schooling FRY and take up into mouth again when necessary until 5 days old 10↶11 (the latter unclear whether it is WILD or FARM12). After females are gone, no data found yet on substrate.
  • FARM: for the related O. niloticus, ponds: rocks or tarpaulin at the bottom (with or without aerial protection nets) 19, shading improves larval development through lower temperatures 14. Further research needed to determine whether this applies to O. aureus as well. For details of holding systems →F1 and F2.
  • LAB: no data found yet.

JUVENILES:

  • WILD: found in open water as well as among stones and vegetation 64↶33, but prefer areas with inundated vegetation 34; burrowing in the mud 29. Non-native habitat: found in waters with aquatic vegetation (macrophytes) 58. Lakes: Secchi disc 0.1-0.2 m 39, 0.2-0.3 m 35.
  • FARM: for the related O. niloticus, ponds: higher growth with added bamboo poles where periphyton grew than without substrate 65, minimal silt on bottom 57, substrate or rocks at the bottom, very turbid water 19. Cages: turbidity: Secchi disc 0.7-1.1 m 66. Further research needed to determine whether this applies to O. aureus as well. For details of holding systems →F1 and F2.
  • LAB: no data found yet.

ADULTS:

  • WILD: found in open water as well as among stones and vegetation 64↶33; burrowing in the mud 29. Lakes: Secchi disc 0.1-0.2 m 39, 0.2-0.3 m 35. Non-native habitat: found in waters with aquatic vegetation (macrophytes) 58.
  • FARM: for the related O. niloticus, ponds: minimal silt on bottom 57. Further research needed to determine whether this applies to O. aureus as well. For details of holding systems →F1 and F2.
  • LAB: no data found yet.

SPAWNERS:

  • WILD: males dig a spawning pit (a shallow depression in the sediment 8) using tail and fins 1. Nesting in sand, among reeds or tamarisk bushes 1, among weeds 5, with soft substrate and sparse-intermediate inundated vegetation 34. Lakes: Secchi disc 0.2-0.3 m 35.
  • FARM: spawning fibreglass tanks: covered with a single polyethylene sheet and a single layer of net shading 7. For the related O. niloticus, ponds: decreasing dissolved oxygen and temperature with increasing shading over hapa nets (no shading, shading on top, half, complete), higher absolute fecundity, spawning rate, number FRY under shading than without 67. Cages with solid base and 25 cm sand layer 22. Tanks: artificial spawning shelters improve reproductive efficiency 14. Hapa nets on tank bottom with mud 16. Further research needed to determine whether this applies to O. aureus as well. For details of holding systems →F1 and F2.
  • LAB: no data found yet.



8  Stress

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, as the species is stressed (water quality, handling, transport). It is medium for high-standard farming conditions, as some ways to reduce (but not avoid) stress are verified for the farming context, others need to be verified for O. aureus. Our conclusion is based on a low amount of evidence, as further species-specific research is needed.

Likelihoodscore-li
Potentialscore-po
Certaintyscore-ce

Eggs:

  • WILD: no data found yet.
  • FARM: for the related O. niloticus, stressed (to the point of mortality) when exposed to ≤17 °C or 39.5 °C directly after fertilisation, best hatching at 28 °C 68. Further research needed to determine whether this applies to O. aureus as well.
  • LAB: no data found yet.

LARVAE and FRY:

  • WILD: no data found yet.
  • FARM: for the related O. niloticus, FRY: higher oxygen consumption and lower short-term growth after 6 h transport in polyethylene bags over bad road than over good road which might be improved through styrofoam pack absorbers 69. Stressed by handling in direct sunlight at noon, rather prefer handling in mornings or evenings and under shade 14, stressed by net material that will cause injuries, slightly larger mesh size that will entangle the gills, abrupt movements, dropping on the floor 14. Further research needed to determine whether this applies to O. aureus as well.
  • LAB: for the related O. niloticus, FRY: stressed by suppression of aeration (hypoxia), which may be reduced by the administration of sulfated polysaccharides (0.05-0.1 mg/g) in the feed (also improving growth) 20. Further research needed to determine whether this applies to O. aureus as well.

JUVENILES:

  • WILD: no data found yet.
  • FARM: for the related O. niloticus, stressed (to the point of mortality) by size grading 70. Cages: higher growth and lower cortisol of genetically improved strain at 75 than 113 and 150 IND/m271. Tanks in RAS: higher growth at 2,000 lux than 1,000 or 3,000 lux, lower cortisol at 18 and 24 h than 12 h PHOTOPERIOD72. Stressed by transport for 4 h in plastic bags with oxygen at density 4 IND/L, even more so at 10 IND/L 73. Further research needed to determine whether this applies to O. aureus as well.
  • LAB: stressed by hypoxia of 5 min 74, exposure to 10 °C (gradually adjusted) 75.

ADULTS:

  • WILD: no data found yet.
  • FARM: no data found yet.
  • LAB: for the related O. niloticus, stressed by netting, even more so if done repeatedly 76. Probably stressed by food competition in group of 15 IND77. No difference in growth under blue, violet, red, green, or yellow light when tested individually, but weight differences in groups of 4 IND except for yellow light with highest variation under red light 78. Stressed by confinement 79 plus white or green but not blue light 80 or more under white than blue light, yellow light in between 81. Higher auditory threshold when exposed to noise for 28 days at 800 Hz 82. Stressed by tailfin clipping 83. Single IND stressed by pairing with dominant IND84 or larger resident, confinement, electric shock 85. Further research needed to determine whether this applies to O. aureus as well.

SPAWNERS:

  • WILD: no data found yet.
  • FARM: stressed (to the point of mortality) by 72 h transport in plastic bags at density 5 IND/L which may be reduced by 0.2-1 g/L clove oil in transport water, but not to cortisol levels of control group 86.
  • LAB: no data found yet.



9  Malformations

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 unclear for minimal and high-standard farming conditions, given we just found unspecific data and information from a related species. Our conclusion is based on a low amount of evidence, as further research is needed.

Likelihoodscore-li
Potentialscore-po
Certaintyscore-ce

Eggs:

  • WILD: no data found yet.
  • FARM: no data found yet.
  • LAB: no data found yet.

LARVAE and FRY:

  • WILD: no data found yet.
  • FARM: tanks: malformations of operculum and curvature of spine when reared in winter, probably due to missing algae compensating for nutrient deficiencies 13.
  • LAB: no data found yet.

JUVENILES:

  • WILD: no data found yet.
  • FARM: for the related O. niloticus, skeletal deformities (lateral projections of the mandible, 'parrot-like head', scoliosis, kyphosis, lordosis, fusion of dorsal and anal fins) in 1.6-2.7% 87. Further research needed to determine whether this applies to O. aureus as well.
  • LAB: no data found yet.

ADULTS:

  • WILD: no data found yet.
  • FARM: no data found yet.
  • LAB: no data found yet.

SPAWNERS:

  • WILD: no data found yet.
  • FARM: no data found yet.
  • LAB: no data found yet.



10  Slaughter

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 (asphyxia, hypothermia, live exsanguination). It is medium for high-standard farming conditions, as electrical stunning – followed by exsanguination, evisceration, or filleting – induces unconsciousness fast (if done correctly) and kills while still unconscious, but needs to be verified for O. aureus. Our conclusion is based on a low amount of evidence, as further species-specific research is needed.

Likelihoodscore-li
Potentialscore-po
Certaintyscore-ce

Eggs: does not apply.

LARVAE and FRY: does not apply.

JUVENILES:

  • WILD: does not apply.
  • FARM: minimal slaughter method: exsanguination while still alive 88. For the related O. niloticus, sold alive 57 at local markets without ice 89 to postpone rigor mortis 14, so probably asphyxia; placing on ice or in refrigerator 8914, so probably asphyxia and/or hypothermia; mainly stunned by live chilling followed by asphyxia, but also followed by exsanguination or decapitation 90. Electrical stunner used in an inappropriate way and without amperage control, not followed by slaughter step resulting in IND receiving improper electrical shocks and being peeled and filleted alive, so probably asphyxia, hypothermia, or during processing 19. High-standard slaughter method: for the related O. niloticus, rapid killing (unspecified) followed by gutting or filleting 89, electronarcosis followed by exsanguination 90, in-water electrical stunning followed by bleeding 91. Further research needed to determine whether this applies to O. aureus as well.
  • LAB: no data found yet.

ADULTS:

  • WILD: does not apply.
  • FARM: probably →JUVENILES, but sources do not specify the age class 12.
  • LAB: no data found yet.

SPAWNERS:

  • WILD: does not apply.
  • FARM: no data found yet.
  • LAB: no data found yet.



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 492, 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: native (artificial lake) and non-native habitat: omnivorous 60379358, but mainly phytoplankton 3, plants and algae 37. FRY: feed on zooplankton 45.
  • FARM: for the related O. niloticus, fish meal may be completely* replaced by non-forage fishery components 94. Ponds: no external feed administered in extensive culture systems 14. Cages: feed without fish meal and fish oil 95. Higher growth of SPAWNERS in fertilised than unfertilised ponds, higher number of hatched FRY at 25-30% protein level for SPAWNERS in pre-spawning period 17. Further research needed to determine whether this applies to O. aureus as well.
  • LAB: FRY: fed on zooplankton 54. Fish meal may be not replaced by one type of non-forage fishery components 96 or sustainable sources 97, but completely* replaced by another type of non-forage fishery components 98.

*partly = <51% – mostly = 51-99% – completely = 100%




Side note: Commercial relevance

How much is this species farmed annually?

 3,100 t/year 1990-2019 amounting to estimated 4,000,000-6,000,000 IND/year 1990-2019 99.




Glossary

ADULTS = mature individuals
BENTHOPELAGIC = living and feeding near the bottom of a body of water, floating above the floor
DOMESTICATION LEVEL 4 = entire life cycle closed in captivity without wild inputs 92
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
FISHES = using "fishes" instead of "fish" for more than one individual - whether of the same species or not - is inspired by Jonathan Balcombe who proposed this usage in his book "What a fish knows". By referring to a group as "fishes", we acknowledge the individuals with their personalities and needs instead of an anonymous mass of "fish".
FRY = larvae from external feeding on
IND = individuals
JUVENILES = fully developed but immature individuals
LAB = setting in laboratory environment
LARVAE = hatching to mouth opening
MOUTHBROODER = also "mouthbreeder"; parent taking eggs into the mouth after fertilisation
PHOTOPERIOD = duration of daylight
POTAMODROMOUS = migrating within fresh water
RAS = Recirculating Aquaculture System - almost completely closed system using filters to clean and recirculate water with the aim of reducing water input and with the advantage of enabling close control of environmental parameters to maintain high water quality
SPAWNERS = adults during the spawning season; in farms: adults that are kept as broodstock
TOTAL LENGTH = from snout to tip of caudal fin as compared to fork length (which measures from snout to fork of caudal fin) or standard length (from head to base of tail fin) or body length (from the base of the eye notch to the posterior end of the telson) 30
WILD = setting in the wild



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