Oreochromis niloticus x O. aureus (Hybrid tilapia): WelfareCheck|farm

Information

Version: C | 1.0 (2025-03-27)

Reviewer: Jenny Volstorf
Editor: Jenny Volstorf

Initial release: 2025-03-27
Version information:

Appearance: C

Cite as: »Marques Maia, Caroline. 2025. Oreochromis niloticus x O. aureus (WelfareCheck | farm). In: fair-fish database, ed. fair-fish. World Wide Web electronic publication. Version C | 1.0. https://fair-fish-database.net.«

WelfareScore | farm

Oreochromis niloticus x O. aureus

LiPoCe

Criteria

Home range

Depth range

Migration

Reproduction

Aggregation

Aggression

Substrate

Stress

Malformations

Slaughter

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)

High

Medium

Low

Unclear

No findings

General remarks

Israeli fish farmers started using an Oreochromis niloticus ♀ x O. aureus ♂ hybrid in the 1960s aiming to prevent uncontrolled propagation of tilapias in production ponds. It is also cultured in Saudi Arabia, with a great interest for aquaculture, especially because it has a better growth and yield than O. niloticus, O. aureus, and O. mossambicus. Furthermore, among several interspecific tilapia hybrids, O. niloticus x O. aureus has shown to be the most suitable one in terms of growth rate, sex ratio, cold tolerance, and body coloration. Stocking hormonally sex reversed FINGERLINGS has become the generalised practice to cope with the uncontrolled spawning issue under farming conditions. Usually, only males are farmed, but 2-3% of the sex-reversed FINGERLINGS remain as females which are still able to spawn in grow-out ponds. Thus, predator species are used to feed on these unwanted eggs, LARVAE, and FRY in warm freshwater aquaculture ponds.

Currently, important information about this hybrid is still missing in the literature, making it difficult to better assess its welfare in farms. Considering wild information, findings about home range as well as aggression and migratory distances is still missing for the parental species O. niloticus, whereas there are important knowledge gaps about home range, depth range, and migration patterns for the parental species O. aureus. Further research on reproduction, stress response, and malformations in farms are urgently needed. Moreover, important farming information about aggregation for the early life stages and substrate use for these age classes and SPAWNERS is still missing.

Note: because this is a hybrid species, we refer to the wild needs and behaviours of the parent species, Oreochromis niloticus and O. aureus, where available, in order to compare them with what the hybrid is provided with in captivity. For a hybrid species, however, welfare studies on the current farming conditions might be even more important than these wild needs.

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 did not find wild data for JUVENILES and ADULTS of the parent species O. niloticus and O. aureus. Our conclusion is based on a medium amount of evidence, as further research is needed on home range in the wild but – maybe more importantly in a hybrid species – on welfare under current farming conditions.

Likelihood score-li

Potential

Certainty

Eggs: does not apply.

LARVAE and FRY:

WILD: O. niloticus: maternally mouthbred 1 2 (non-native habitat: 3 4 5). MOUTHBROODER females release FRY1 after yolk sac absorption, maximum 13.5 mm TOTAL LENGTH6, guard over clouds of FRY1, external feeding from 15 mm on 7. After females are gone, no data found yet on home range. O. aureus: maternally mouthbred 8 9 10 11 12 13 14 15. MOUTHBROODER females release FRY not before 10 mm TOTAL LENGTH8, stay close to schooling FRY and take up into mouth again when necessary until 5 days old 16↶17 (the latter unclear whether it is WILD or FARM18). After females are gone, no data found yet on home range.
FARM: hatch in female’s mouth in 400 m² ponds 19 or in 6-50 m²20 concrete tanks 21 20. From concrete tanks, FRY are moved to 900 L fibreglass tanks 21.
LAB: does not apply.

JUVENILES:

WILD: O. niloticus and O. aureus: no data found yet.
FARM: ponds: 300-400 m²19 22 23, 18,000 m²24, concrete ponds with BIOFLOC: 50 m²25. Cages: 1.5 m² (1.5 x 1 m) 26, 4 m³27; cages in ponds: 1 m³24; cages in lagoons: 3 m³28. Tanks: 13-40 m³28; overwintering tanks: 4 m² (2 x 2 m) 19; outdoor concrete tanks (young IND): 10 m² (3.8 x 2.6 m) 21; outdoor tanks with BIOFLOC: 18.6 m² (16.6 m³) 29.
LAB: does not apply.

ADULTS:

WILD: O. niloticus and O. aureus: no data found yet.
FARM: ponds: 300-400 m²19 22 23 30, 1,000 m²19, 18,000 m²24. Cages in ponds: 1 m³24; cages in lagoons: 3 m³28. Tanks: 13-40 m³28.
LAB: does not apply.

SPAWNERS:

WILD: O. niloticus: nests may be >1 m ∅ 1. Non-native habitat: bowers with pit of 0.4-1.9 m ∅ 31, nests of range 0.05-1 m ∅, mean 0.4-0.6 m ∅ 32. MOUTHBROODER females stay inactive until FRY require external feed, then move to shallow areas 33 and guard FRY1, external feeding from 15 mm on 7. O. aureus: nests of 0.4 m ∅ 11, 0.9 m ∅ 8. Maternal MOUTHBROODER8 9 10 11 12 13 14 15. MOUTHBROODER females release FRY not before 10 mm TOTAL LENGTH8, stay close to schooling FRY and take up into mouth again when necessary until 5 days old 16↶17 (the latter unclear whether it is WILD or FARM18).
FARM: concrete indoor tanks: 50 m²21, concrete holding tanks: 12 m² (4 x 3 m), concrete spawning tanks: 6 m² (3 x 2 m) 20.
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 given up to 4-30 m depth range in O. niloticus and in case the unclear depth range is fully used (mean 9 m) in O. aureus, as ponds, cages, and tanks do not cover the whole range in the wild. It is medium for high-standard farming conditions, as the mentioned systems at least overlap with the range in the wild. Our conclusion is based on a medium amount of evidence, as further research is needed on depth range in the wild and – maybe more importantly in a hybrid species – on welfare under current farming conditions.

Likelihood score-li

Potential

Certainty

Eggs:

WILD: O. niloticus: maternally mouthbred 1 2 (non-native habitat: 3 4 5). O. aureus: maternally mouthbred 8 9 10 11 12 13 14 15.
FARM: hatch in female’s mouth in ponds 19 or in concrete tanks 21 20. Ponds: 1 m 19.
LAB: does not apply.

LARVAE and FRY:

WILD: O. niloticus: maternally mouthbred 1 2 (non-native habitat: 3 4 5). MOUTHBROODER females move to shallow areas 1 (non-native habitat: MOUTHBROODER females in 0-4 m littoral 4), release FRY1 after yolk sac absorption, maximum 13.5 mm TOTAL LENGTH6, guard over clouds of FRY1, external feeding from 15 mm on 7. After females are gone, abundant in littoral <4 m 36, at 0.05-0.3 m during the day, deeper at night 7. O. aureus: maternally mouthbred 8 9 10 11 12 13 14 15. After spawning, MOUTHBROODER females move to deeper waters 16↶17 37↶17, unclear whether it is WILD or FARM18. FRY: rivers: 0.5-1.5 m (non-native habitat: 38) with unclear depth range use.
FARM: hatch in female’s mouth in ponds 19 or in concrete tanks 21 20. From concrete tanks, FRY are moved to fibreglass tanks 21. Ponds: 1 m 19.
LAB: does not apply.

JUVENILES:

WILD: O. niloticus: caught at 0-4 m 39, ≤10 m, seldomly at 10-30 m 40; non-native habitat: caught at 0-4 m 4, ≤10 m 41, 0-15 m 42, at 12-16 m during day and night 43, some ≤20 m 42. Caught in lakes of 0.8-6.4 m 2, 2-4.9 m (non-native habitat: 44), 20 m (non-native habitat: 45↶46) with unclear depth range use. Seldomly in open water and deeper depths at low turbidity 40, but also on the bottom in thick deposit of organic mud (non-native habitat: 43). Non-native habitat: moving between littoral with vegetation close to shore 4 and deeper off shore with sandy or rocky bottom 41; detritus in stomach indicates bottom grazing 44 47 48 49. O. aureus: BENTHOPELAGIC50, preferring shallow waters 51. Lakes: 0.5-1.9 m 52, lake Maryut 11 with 0.6-2.7 m 53, artificial lake of 1-1.5 m 54, average 1.4 m 55, ca 2 m max 56, average 2.6 m 57, all with unclear depth range use; rivers: caught at 0.5-2.4 m (non-native habitat: 58); Rosetta branch of Nile river: 2-4 m 59↶60, rivers: 0.5-1.5 m (non-native habitat: 38), mean 9 m (non-native habitat: 15), all with unclear depth range use.
FARM: ponds: 1-3 m 19 24, shallow 22; concrete ponds with BIOFLOC: 1 m 25. Cages: 1.2 m 26; cages in ponds: 1 m 24. Outdoor tanks with BIOFLOC: 0.9 m 29; outdoor concrete tanks (young IND): 0.5 m 21; overwintering tanks: 1 m 19.
LAB: does not apply.

ADULTS:

WILD: O. niloticus: →JUVENILES. O. aureus: BENTHOPELAGIC50. Lakes: 0.5-1.9 m 52, lake Maryut 11 with 0.6-2.7 m 53, artificial lake of 1-1.5 m 54, average 1.4 m 55, ca 2 m max 56, average 2.6 m 57, all with unclear depth range use; rivers: caught at 0.5-2.4 m (non-native habitat: 58); Rosetta branch of Nile river: 2-4 m 59↶60, rivers: mean 9 m (non-native habitat: 15), all with unclear depth range use.
FARM: ponds: 1-3 m 19 24, shallow 22. Cages in ponds: 1 m 24.
LAB: does not apply.

SPAWNERS:

WILD: O. niloticus: nests in 0.6-1.2 m 1. Non-native habitat: bowers with pit of 0.4-1.4 m depth, rim height of 0.01-0.5 m 31, nesting depth 0.8-1.4 m 32, MOUTHBROODER females in 0-4 m littoral 4. O. aureus: lakes: 0.5-1.9 m 52, lake Maryut 11 with 0.6-2.7 m 53, all with unclear depth range use; rivers: mean 9 m (non-native habitat: 15) with unclear depth range use. Nesting in <2 m (mainly at 0.3-0.8 m) 51, 0.6-0.9 m 8, and in shallow lagoon habitats, but also in open-shore areas with inundated vegetation 51. Nests are holes of ≤0.5 m depth 8. Maternal MOUTHBROODER8 9 10 11 12 13 14 15. After spawning, MOUTHBROODER females swim to deeper waters 16↶17 37↶17, unclear whether it is WILD or FARM18.
FARM: concrete indoor tanks: 0.5 m 21, concrete holding tanks: 1 m, concrete spawning tanks: 0.5 m 20.
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 given that the parent species O. niloticus and O. aureus undertake more or less extensive migrations (even though of partly 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 the lower end of the migration distance is unknown and therefore also the degree to which the space range in captivity potentially overlaps with it. Our conclusion is based on a medium amount of evidence, as further research is needed on specific migration distances in the wild and – maybe more importantly in a hybrid species – on welfare under current farming conditions.

Likelihood score-li

Potential

Certainty

Parental species: O. niloticus: possibly POTAMODROMOUS7 61. O. aureus: POTAMODROMOUS61.

Eggs: does not apply.

LARVAE and FRY:

WILD: O. niloticus: maternally mouthbred in fresh 2 (non-native habitat: 4) or brackish water 1 39 (non-native habitat: 5). Afterwards, abundant inshore 36, but present in all parts of the lake 7. Movement from one lake side to the opposite (lake breadth: 13-44 km), probably assisted by lake currents 7. O. aureus: maternally mouthbred in brackish 8 62 11 52 63 to saline waters 11 63.
FARM: for details of holding systems → F1 and F2.
LAB: no data found yet.

JUVENILES:

WILD: O. niloticus: mainly in inshore waters of one (brackish) lake, sometimes moving offshore 1, in other lake: mostly open water 1, probably disperse after nursery phase into open waters 7. Non-native habitat: feeding at lake edges, in lagoons in estuaries of inflowing rivers, living off-shore in lakes 3, moving between littoral with vegetation close to shore and deeper off shore with sandy or rocky bottom 41. O. aureus: brackish water 11 52 56 57 to saline waters 11.
FARM: cages in lagoon: salinity ≤15 ppt (oligo-mesohaline waters) 28. Tanks: salinity ≤15 ppt (oligo-mesohaline waters) 28. For details of holding systems → F1 and F2.
LAB: no data found yet.

ADULTS:

WILD: O. niloticus: →JUVENILES. O. aureus: brackish water 62 11 52 56 57 to saline waters 11.
FARM: →JUVENILES.
LAB: no data found yet.

SPAWNERS:

WILD: O. niloticus: fresh (non-native habitat: 4) or brackish water 1 39. If not already inshore, move there from open water to breed 1 7. MOUTHBROODER females stay inactive until FRY require external feed, then move to shallow areas 33. O. aureus: maternal MOUTHBROODER in brackish 8 62 11 52 to saline waters 11. Breed close to shore 8. After spawning, MOUTHBROODER females swim to deeper waters 16↶17 37↶17, unclear whether it is WILD or FARM18.
FARM: for O. aureus, spawning fibreglass tanks: salinity: 3-5 g/L (low-salinity underground water) 13. Further research needed to determine whether this applies to the hybrid as well. 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 and – maybe more importantly in a hybrid species – on welfare under current farming conditions.

Likelihood score-li

Potential

Certainty

Eggs: does not apply.

LARVAE and FRY: does not apply.

JUVENILES: does not apply.

ADULTS: does not apply.

SPAWNERS:

WILD: O. niloticus: mature in first year of life (non-native habitat: 4), spawn throughout the year 7 (non-native habitat: 4) every 30-90 days (non-native habitat: 5) in batches (non-native habitat: 64). MOUTHBROODER: female takes eggs in mouth after fertilisation 1 7 2 (non-native habitat: 4 5) until after yolk sac absorption, maximum 13.5 mm TOTAL LENGTH6, and guards them 1, external feeding from 15 mm on 7. For nest building →F3. O. aureus: start maturing at 3 months of age 14, non-native habitat: 1.5-2.5 years, females earlier than males 65. Spawning season: April-August 66 13 51 (spring-early summer 51), Feb-Nov with peaks in May and Sept-Oct 67, non-native habitat: year round 68 69, highest activity January-May 69 or peak in July 68. Multiple spawnings 12 14, asynchronously 12. Courting behaviour in the nest: male displays to female 8, lateral display by both sexes with nipping and tail-flapping 16↶17 37↶17 (the latter unclear whether it is WILD or FARM18). Maternal MOUTHBROODER8 9 10 11 12 13 14 15, females take eggs in mouth after fertilisation 8, caring from eggs to FRY14: stay close to FRY and take up into mouth again when necessary until 5 days old 16↶17 (the latter unclear whether it is WILD or FARM18). For nest building →F3.
FARM: spawn at 1-4 years old 21 20 with more eggs in 1 year olds than 2-4 years 20; males mature earlier than females 21. Sex ratio: 1:2-5 males:females 21 20 with higher eggs/females/day and kg/female/day at 1:2 and 1:3 20. Natural spawning without manipulation 21 20. Spawn asynchronously and successively throughout the breeding season 21. Female MOUTHBROODER, eggs are left to hatch in female’s mouth 21 20.
LAB: no data found yet.

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 hapas, cages, tanks, and some ponds go beyond the smallest density of the parent species O. niloticus and O. aureus in the wild (although we cannot be sure in all age classes). It is medium for high-standard farming conditions, as densities in other ponds at least overlap with the density range in the wild. Our conclusion is based on a high amount of evidence, unless farm studies show that hybrid tilapia is well under higher densities than its parent species in the wild.

Likelihood score-li

Potential

Certainty

Eggs: does not apply.

LARVAE and FRY:

WILD: O. niloticus: maternally mouthbred 1 2 (non-native habitat: 3 4 5). MOUTHBROODER females release FRY1 after yolk sac absorption, maximum 13.5 mm TOTAL LENGTH6, guard over clouds of FRY1, external feeding from 15 mm on 7. After females are gone, live in shoals 1 7 or schools (non-native habitat: 70). Estimated density in bed of Potamogeton pectinatus of IND 16-126 mm TOTAL LENGTH: 3.1 IND/m² or 0.01 kg/m²36. Non-native habitat: at 10-30 mm TOTAL LENGTH: 12-30 IND/m²4. O. aureus: maternally mouthbred 8 9 10 11 12 13 14 15. MOUTHBROODER females release FRY not before 10 mm TOTAL LENGTH8, stay close to schooling FRY and take up into mouth again when necessary until 5 days old 16↶17 (the latter unclear whether it is WILD or FARM18). After females are gone, no data found yet on aggregation type.
FARM: hatch in female’s mouth in ponds 19 or in concrete tanks 21 20. From concrete tanks, FRY are moved to fibreglass tanks 21. For O. niloticus, hatch in female’s mouth in breeding ponds (females leave when FRY reach 9-10 mm TOTAL LENGTH) 71 or are collected from female’s mouth 72 71 every 5-7 days 73 71, 10 days 74. FRY: stocking in FINGERLINGS ponds: 10 IND/m²71, nursery ponds: 100-200 IND/m²71, 500 IND/m³ (concrete) 74, 1,000 IND/m²75. Incubation systems: 5 IND/L, hapas in earthen ponds: 1,000-2,000 IND/m²71. Higher growth in hapa nets with 250 IND/m² than hapa nets with 1,000 IND/m² and concrete tanks with 1,000 IND/m²76. Cages: survival >75% at 1,000-3,000 IND/m³ for pre-growing IND to 2 months, decreasing survival at densities beyond that 77, 800 IND/m² for pre-growing 2 months old IND to 5 months 77, higher growth of monosex male FINGERLINGS at 400 IND/m² than 500 or 600 IND/m²78. For O. aureus, are collected from female’s mouth every 14 days 79. Further research needed to determine whether this applies to the hybrid as well.
LAB: no data found yet

JUVENILES:

WILD: O. niloticus: shoal when in open water 1. Estimated density in bed of Potamogeton pectinatus of IND 16-126 mm TOTAL LENGTH: 3.1 IND/m² or 0.01 kg/m²36, estimated density from bottom trawls: 0.00003 kg/m²40. Non-native habitat: 0.001-0.01 IND/m² given type of vegetation 4. O. aureus: schooling 50; 0-5 IND/m²51.
FARM: ponds: 0.5 IND/m² in polyculture with Cyprinus carpio, Mugil cephalus, and Hypophthalmichthys molitrix of overall density of 2 IND/m²24; 1.5 IND/m² in polyculture with predators (Morone saxatilis x M. chrysops and Sciaenops ocellatus) to reduce uncontrolled spawning of overall density of 1.6 IND/m²22; 0.6-1.4 IND/m² in polyculture with C. carpio, H. molitrix, and Ctenopharyngodon idella of overall density of 1.1-2 IND/m²19, 0.8 IND/m² in polyculture with C. carpio, H. molitrix, C. idella, and red tilapia of overall density of 1.5 IND/m²19 organic culture (~half density than in conventional ponds): 1.2 IND/m² in polyculture with C. idella, hybrid carp (H. molitrix x H. nobilis), C. carpio, a mullet species, and predator species to reduce uncontrolled spawning of overall density of 1.4 IND/m²23; concrete ponds with BIOFLOC: 320 IND/m² (young IND), 163-184 IND/m² (older IND) 25. Cages: 17 IND/m³26 (ca 20 IND/m²18); better growth at 10 IND/m³ than at 18 IND/m³27; cages in ponds: 50 IND/m³24 (ca 50 IND/m²18); cages in lagoon: 33 IND/m³28. Tanks: 7.5-8 IND/m³28; outdoor tanks with BIOFLOC: 25 IND/m² (29 IND/m³) 29; outdoor concrete tanks (young IND): 40 IND/m²21.
LAB: no data found yet.

ADULTS:

WILD: O. niloticus: shoal when in open water 1. Non-native habitat: 0.001-0.01 IND/m² given type of vegetation 4. O. aureus: schooling 50.
FARM: ponds: 0.5 IND/m²in polyculture with C. carpio, M. cephalus, and H. molitrix of overall density of 2 IND/m²24; 1.5 IND/m² in polyculture with predators (M. saxatilis x M. chrysops and S. ocellatus) to reduce uncontrolled spawning of overall density of 1.6 IND/m²22; 0.7 IND/m² in polyculture with C. carpio, H. molitrix, and C. idella of overall density of 1.1-1.2 IND/m²19, 0.9 IND/m² in polyculture with C. carpio, H. molitrix, C. idella, and red tilapia of overall density of 1.4 IND/m²19; organic culture (~half density than in conventional ponds): 1.2 IND/m² in polyculture with H. molitrix, C. idella, and Sciaenops ocellatus or with C. idella, hybrid carp (H. molitrix x H. nobilis), C. carpio, a mullet species, and predator species to reduce uncontrolled spawning of overall density of 1.4 IND/m²23 30. Cages in ponds: 50 IND/m³24 (ca 50 IND/m²18); cages in lagoon: 33 IND/m³28. Tanks: 7.5-8 IND/m³28.
LAB: no data found yet.

SPAWNERS:

WILD: O. niloticus: spotted once: round shoals of several 100 IND with 3 m ∅, possibly in connection with breeding habit 1. Non-native habitat: bowers distributed in pond at 0.01-0.02 bowers/m²31, nests aggregated in reservoir at 0.2-0.6 nests/m² (the higher the turbidity the higher the nest density) 32. MOUTHBROODER females form small groups until FRY require external feed, then separate to care for FRY individually 33. O. aureus: males visit female schools and attempt to attract a female spawning partner 16↶17 37↶17, unclear whether it is WILD or FARM18. Nests with 1 m distance from each other 11.
FARM: concrete indoor tanks: 4 IND/m²21, concrete holding tanks: 35 females/m² or 13 males/m², concrete spawning tanks: 2-5 IND/m² with more eggs/female/day and eggs/kg/day under 2 IND/m²20.
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 there are hints for aggression in all age classes. It is medium for high-standard farming conditions, as ways to reduce (but not avoid) aggression (amount feeding, keeping separate, size grading, density) are verified for the farming context. Our conclusion is based on a medium amount of evidence, as further (species-specific) research is needed.

Likelihood score-li

Potential

Certainty

Eggs: does not apply.

LARVAE and FRY:

WILD: O. niloticus: maternally mouthbred 1 2 (non-native habitat: 3 4 5). MOUTHBROODER females release FRY1 after yolk sac absorption, maximum 13.5 mm TOTAL LENGTH6, guard over clouds of FRY1, external feeding from 15 mm on 7. After females are gone, live in shoals 1 7 or schools (non-native habitat: 70), thus probably no aggression. O. aureus: maternally mouthbred 8 9 10 11 12 13 14 15. MOUTHBROODER females release FRY not before 10 mm TOTAL LENGTH8, stay close to schooling FRY and take up into mouth again when necessary until 5 days old 16↶17 (the latter unclear whether it is WILD or FARM18). After females are gone, no data found yet on aggression.
FARM: hatch in female’s mouth in ponds 19 or in concrete tanks 21 20. From concrete tanks, FRY are moved to fibreglass tanks 21. FRY: cannibalism caused 10-35% mortality rate, inversely related to the level of feeding 80.
LAB: no data found yet.

JUVENILES:

WILD: O. niloticus: no data found yet. O. aureus: territorial 50. Non-native habitat: cannibalism of youngs 81; competition for space and food 68.
FARM: no aggression reported in polyculture with C. idella, hybrid carp (H. molitrix x H. nobilis), C. carpio, mullet species, and predator species to reduce uncontrolled spawning 23. Kept separately from other hybrids or tilapia species to avoid aggressive behaviours 28. Parental strains resulting in low number of hybrid males lead to considerable uncontrolled reproduction and increased competition, eventually decreasing growth in other polyculture species (carps, other tilapia hybrids) 19.
LAB: no data found yet.

ADULTS:

WILD: O. niloticus: no data found yet. O. aureus:→JUVENILES.
FARM: no aggression reported in polyculture with H. molitrix, C. idella and S. ocellatus30 or with C. idella, hybrid carp (H. molitrix x H. nobilis), C. carpio, mullet species, and predator species to reduce uncontrolled spawning 23, no aggression reported. Kept separately from other hybrids or tilapia species to avoid aggressive behaviours 28. Parental strains resulting in low number of hybrid males lead to considerable uncontrolled reproduction and increased competition, eventually decreasing growth in other polyculture species (carps, other tilapia hybrids) 19.
LAB: no data found yet.

SPAWNERS:

WILD: O. niloticus: no data found yet. O. aureus: male guards nest 62.
FARM: for 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 71. Increasing aggression with increasing density 71. Further research needed to determine whether this applies to the hybrid as well.
LAB: no data found yet.

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 parent species O. niloticus and O. aureus use substrate, but hapas, cages, and some ponds and 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 with (plastic) substrate for FRY to ADULTS which are not replaced by tarpaulin or concrete bottom, and given c) natural reproduction with spawning substrate in ponds or cages for SPAWNERS which need to be verified for the hybrid. Our conclusion is based on a medium amount of evidence, as further species-specific research is needed

Likelihood score-li

Potential

Certainty

Eggs:

WILD: O. niloticus: maternally mouthbred 1 2 (non-native habitat: 3 4 5). O. aureus: maternally mouthbred 8 9 10 11 12 13 14 15.
FARM: hatch in female’s mouth in ponds 19 or in concrete tanks 21 20. For O. niloticus, hatch in female’s mouth in breeding ponds (females leave when FRY reach 9-10 mm TOTAL LENGTH) 71 or are collected from female’s mouth 72 71 every 5-7 days 73 71, 10 days 74. Ponds: shading increases hatching rate through lower temperatures 71. Further research needed to determine whether this applies to the hybrid as well. For details of holding systems → F2.
LAB: no data found yet.

LARVAE and FRY:

WILD: O. niloticus: maternally mouthbred 1 2 (non-native habitat: 3 4 5), afterwards over sand (non-native habitat: 4) along shores or in muddy lagoons 1, in well-sheltered gulfs or bays 36, among inundated vegetation 7, seek shelter of macrophytes at night 7. O. aureus: maternally mouthbred 8 9 10 11 12 13 14 15. MOUTHBROODER females release FRY not before 10 mm TOTAL LENGTH8, stay close to schooling FRY and take up into mouth again when necessary until 5 days old 16↶17 (the latter unclear whether it is WILD or FARM18). After females are gone, no data found yet on substrate.
FARM: hatch in female’s mouth in ponds 19 or in concrete tanks 21 20. From concrete tanks, FRY are moved to fibreglass tanks 21. For O. niloticus, hatch in female’s mouth in breeding ponds (females leave when FRY reach 9-10 mm TOTAL LENGTH) 71 or are collected from female’s mouth 72 71 every 5-7 days 73 71, 10 days 74. Ponds: rocks or tarpaulin at the bottom (with or without aerial protection nets) 75, shading improves larval development through lower temperatures 71. Further research needed to determine whether this applies to the hybrid as well. For details of holding systems → F1 and F2.
LAB: no data found yet.

JUVENILES:

WILD: O. niloticus: live along sheltered sandy beaches 1, in well-sheltered gulfs or bays 36, over sand and mud 2 (non-native habitat: 4 5 82). Seldomly in open water and deeper depths at low turbidity 40, but also on the bottom in thick deposit of organic mud (non-native habitat: 43). Non-native habitat: moving between littoral with vegetation close to shore 4 and deeper off shore with sandy or rocky bottom 41; detritus in stomach indicates bottom grazing 44 47 48 49; seek shelter from predatory Lates niloticus in complex wetlands 83↶47 84↶47 85↶47 86↶47; Secchi disc depth 0.2 m 44, 0.7-0.8 44 47. Higher abundance at lower transparency and higher abundance in structurally complex wetlands compared to open water might indicate taking shelter from Lates niloticus47. O. aureus: found in open water as well as among stones and vegetation 87↶50, but prefer areas with inundated vegetation 51; burrowing in the mud 88. Non-native habitat: found in waters with aquatic vegetation (macrophytes) 81. Lakes: Secchi disc 0.1-0.2 m 56, 0.2-0.3 m 52.
FARM: concrete ponds with BIOFLOC: covered with polyethylene sheets for overwintering 25. Ponds: submerged plastic substrates for periphyton growth (equivalent to 40% of the pond surface) 23; turbidity: 0.3-0.5 m 23. For details of holding systems → F1 and F2.
LAB: no data found yet.

ADULTS:

WILD: O. niloticus: →JUVENILES. O. aureus: found in open water as well as among stones and vegetation 87↶50; burrowing in the mud 88. Lakes: Secchi disc 0.1-0.2 m 56, 0.2-0.3 m 52. Non-native habitat: found in waters with aquatic vegetation (macrophytes) 81.
FARM: ponds: submerged plastic substrates for periphyton growth (equivalent to 40-50% of the pond surface) from the surface to 0.2 m above the bottom 23 30; turbidity: 0.3-0.5 m 23. For details of holding systems → F1 and F2.
LAB: no data found yet.

SPAWNERS:

WILD: O. niloticus: male builds nest in sand or inshore reed areas 1, in sandy sheltered conditions 7. Non-native habitat: bowers in sediment of mud and fine sand or silt and fine sand with 0-9.2 m distance to vegetation 31, nests in medium and fine sand at turbidity 3.1-11.3 NTU (the higher the turbidity the higher the nest density), sometimes covered by vegetation 32, MOUTHBROODER females in littoral with vegetation 4. O. aureus: males dig a spawning pit (a shallow depression in the sediment 14) using tail and fins 8. Nesting in sand, among reeds or tamarisk bushes 8, among weeds 11, with soft substrate and sparse-intermediate inundated vegetation 51. Lakes: Secchi disc 0.2-0.3 m 52.
FARM: for 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 89. Cages with solid base and 25 cm sand layer 77. Tanks: artificial spawning shelters improve reproductive efficiency 71. Hapa nets on tank bottom with mud 73. For O. aureus, spawning fibreglass tanks: covered with a single polyethylene sheet and a single layer of net shading 13. Further research needed to determine whether this applies to the hybrid 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 parent species O. niloticus and O. aureus are stressed (water quality, handling, confinement, crowding, transport). It is medium for high-standard farming conditions, as most ways to reduce (but not avoid) stress need to be verified for the hybrid. Our conclusion is based on a low amount of evidence, as further species-specific research is needed.

Likelihood score-li

Potential

Certainty

Eggs:

WILD: O. niloticus and O. aureus: no data found yet.
FARM: for 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 90. Further research needed to determine whether this applies to the hybrid as well.
LAB: for O. niloticus, higher hatching and higher survival rate in round-bottom than conical hatching jars, probably due to less mechanical stress through less friction 90. Further research needed to determine whether this applies to the hybrid as well.

LARVAE and FRY:

WILD: O. niloticus and O. aureus: no data found yet.
FARM: for 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 91. Stressed by handling in direct sunlight at noon, rather prefer handling in mornings or evenings and under shade 71, stressed by net material (that will cause injuries), slightly larger mesh size (that will entangle the gills), abrupt movements, dropping on the floor 71. Further research needed to determine whether this applies to the hybrid as well.
LAB: for O. niloticus, 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) 92. Further research needed to determine whether this applies to the hybrid as well.

JUVENILES:

WILD: O. niloticus and O. aureus: no data found yet.
FARM: cages in ponds: pathological alterations proposed as a consequence of stressful conditions under a density of 50 IND/m³ in cages of 1 m³, which may be minimised by 150 mg/kg of L-carnitine in the diet 24.
LAB: for O. niloticus, higher stress in groups of 10 than in singly-held IND or pairs, indicating crowding stress 93. Stressed by chasing with net for 60 s 93 94. Stressed by handling 95 96 which could not be reduced with eugenol but made handling IND easier 95, anaesthetisation with clove oil (250 m/L) more successive, but induced some stress itself 96. Stressed (to the point of mortality) under 24 h or 0 h PHOTOPERIOD compared to 12 h PHOTOPERIOD97. No difference in ventilatory frequency under white, blue, or yellow light when tested individually 98. Higher cortisol levels in IND exposed to water from stressed conspecifics than in control group 94. Individual differences in boldness: males with more number of returns to and more time spent in former confinement area also displayed lower cortisol levels after emerged netting, faster food intake recovery in a novel environment, less neophobia towards a novel object, and more body displacements in an emerged net, indicating boldness 99; males escaping faster from a confinement situation also returned to the area the confinement took place slower, spent less time there, and displayed higher cortisol levels, indicating stress 99. Higher frequency of “comfort behaviour” (chafing, resting, surfacing, elimination) at 100 than 200 or 400 IND/m³, no effect on schooling, increasing cortisol levels with increasing density 100. Lower ventilatory frequency when provided with artificial water hyacinth (frayed nylon rope) than shelters (PVC pipes), 2.6% tryptophan in diet, or control 101. Higher cortisol levels in 50% than 100% cover indicating disadvantage of 50% cover 102. For O. aureus, stressed by hypoxia of 5 min 103, exposure to 10 °C (gradually adjusted) 104. Further research needed to determine whether this applies to the hybrid as well.

ADULTS:

WILD: O. niloticus and O. aureus: no data found yet.
FARM: →JUVENILES.
LAB: for O. niloticus, stressed by netting, even more so if done repeatedly 105. Probably stressed by food competition in group of 15 IND106. 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 107. Stressed by confinement 108 plus white or green but not blue light 109 or more under white than blue light, yellow light in between 98. Higher auditory threshold when exposed to noise for 28 days at 800 Hz 110. Stressed by tailfin clipping 111. Single IND stressed by pairing with dominant IND112 or larger resident, confinement, electric shock 113. Further research needed to determine whether this applies to the hybrid as well.

SPAWNERS:

WILD: O. niloticus and O. aureus: no data found yet.
FARM: for O. niloticus, extraction of eggs from mouth of female by lowering pond water level from 0.7 to 0.2 m, scooping female out and placing on plate, which frightened female so that she released eggs 72. For O. aureus, 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 114. Further research needed to determine whether this applies to the hybrid as well.
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 high for minimal and high-standard farming conditions, as malformation rates of the parent species O. niloticus does not exceed 10%. Our conclusion is based on a low amount of evidence, as further species-specific research is needed.

Likelihood score-li

Potential

Certainty

Eggs:

WILD: O. niloticus and O. aureus:no data found yet.
FARM: no data found yet.
LAB: no data found yet.

LARVAE and FRY:

WILD: O. niloticus and O. aureus:no data found yet.
FARM: for O. niloticus, deformities in 3.3-8.3% of IND, with no effect of amount of inbreeding 115. For O. aureus, tanks: malformations of operculum and curvature of spine when reared in winter, probably due to missing algae compensating for nutrient deficiencies 79. Further research needed to determine whether this applies to the hybrid as well.
LAB: no data found yet.

JUVENILES:

WILD: O. niloticus and O. aureus:no data found yet.
FARM: cages in ponds: pathological alterations proposed as a consequence of stressful conditions under a density of 50 IND/m³ in cages of 1 m³, which may be minimised by 150 mg/kg of L-carnitine in the diet 24. For 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% 116. Further research needed to determine whether this applies to the hybrid as well.
LAB: no data found yet.

ADULTS:

WILD: O. niloticus and O. aureus:no data found yet.
FARM: →JUVENILES.
LAB: no data found yet.

SPAWNERS:

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

Likelihood score-li

Potential

Certainty

Eggs: does not apply.

LARVAE and FRY: does not apply.

JUVENILES:

WILD: does not apply.
FARM: minimal slaughter method: for O. aureus, exsanguination while still alive 117; for O. niloticus, sold alive 118 at local markets without ice 119 to postpone rigor mortis 71, so probably asphyxia; placing on ice or in refrigerator 119 71, so probably asphyxia and/or hypothermia; mainly stunned by live chilling followed by asphyxia, but also followed by exsanguination or decapitation 120. 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 75. High-standard slaughter method: for O. niloticus, rapid killing (unspecified) followed by gutting or filleting 119, electronarcosis followed by exsanguination 120, in-water electrical stunning followed by bleeding 121. Further research needed to determine whether this applies to the hybrid as well.
LAB: no data found yet.

ADULTS:

WILD: does not apply.
FARM: probably → JUVENILES, but sources do not specify the age class 18.
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?

Hybrid: DOMESTICATION LEVEL 518, 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: O. niloticus: opportunistic – either mainly herbivorous 7 (non-native habitat: 44 43 48 123 82) or mainly omnivorous (non-native habitat: 4 47 42 49). O. aureus: native (artificial lake) and non-native habitat: omnivorous 124 54 125 81, but mainly phytoplankton 10, plants and algae 54. FRY: feed on zooplankton 63.
FARM: ponds: hard plastic substrates for periphyton growth equivalent to 50% of the pond surface may reduce up to 40% in the feed amount supplied 30. Fish meal may be completely* replaced by non-forage fishery components, but with the inclusion of fish oil 26.
LAB: JUVENILES: fish meal may be completely* replaced by sustainable sources in fresh water but not in brackish water (20%) – with even higher mortality 126; fish oil may be mostly* and fish meal may be completely* replaced by a mix of sustainable sources and non-forage fishery components 127; fish meal may be partly* 128 129 or mostly* 129 replaced by sustainable sources but with an increase in fish oil; fish meal may be partly* replaced by sustainable sources 130; fish meal may be completely* replaced by non-forage fishery components 131; fish oil may be completely* replaced by sustainable sources 132. JUVENILES-ADULTS: fish meal and fish oil may be partly* replaced by sustainable sources 133.

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

Side note: Commercial relevance

How much is this species farmed annually?

410,553 t/year 1990-2019 amounting to estimated 681,000,000 IND/year 1990-2019 134.

Glossary

ADULTS = mature individuals
BENTHOPELAGIC = living and feeding near the bottom of a body of water, floating above the floor
BIOFLOC = dense microbial communities growing in flocs 35
DOMESTICATION LEVEL 5 = selective breeding programmes are used focusing on specific goals 122
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
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
NTU = Nephelometric Turbidity Units
PHOTOPERIOD = duration of daylight
POTAMODROMOUS = migrating within fresh water
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) 34
WILD = setting in the wild

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