Reviewer: Billo Heinzpeter Studer
Editor: Billo Heinzpeter Studer

Initial release: 2015-01-15
Version information:

• Appearance: B
• Last minor update: 2022-01-22

Cite as: »Volstorf, Jenny, and Caroline Marques Maia. 2022. Oreochromis niloticus (Dossier). In: fair-fish database, ed. fair-fish. World Wide Web electronic publication. Version B | 1.1. https://fair-fish-database.net.«

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• Unpredictable influence: no data found yet.
• Competition:
  • Observations WILD: food competitors to native species (axolotl) 1.
• Disease transmission: no data found yet.
• Interbreeding: no data found yet.

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• For breeding ➝ 2 3.

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• For daily rhythm ➝ 4 5.
• For nest building ➝ 6 7 8 9 10.
• For courtship ➝ 7 9.
• For breeding ➝ 11.
• For acoustic communication ➝ 12.
• For shoaling ➝ 13.
• For dominance and subordination ➝ 14 15 16 17 7 18 19 20 21 8 22 23.
• For aggression ➝ 16 19 21 24.
• For learning ➝ 4 25 26.
• For coping styles ➝ 20 27 26.
• For observable stress reactions ➝ 28 20 29.

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• Observations: coastal rivers of Israel 31↶32, Nile basin 33↶32, West Africa 34↶32.

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• Observations Africa: Nyanza Gulf of lake Victoria, Kenya 35, lake Nyamusingiri and lake Kyasanduka, Uganda 36, lake Nabugabo, Uganda 37, Ero reservoir, Nigeria 38, Limpopo river, South Africa 39.
• Observations North America: Mississippi bayou, USA 2, Xochimilco wetland, Mexico 1.

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• Observations Nile perch WILD: Lates niloticus: lake Nyamusingiri and lake Kyasanduka, Uganda (introduced) 36, lake Nabugabo, Uganda (introduced) 37.
• Observations Mozambique tilapia WILD: Oreochromis mossambicus: Limpopo river, South Africa (introduced) 39.

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• Plants: no data found yet.
• Rocks and stones:
  • For substrate and nest building ➝ D1.
• Sand and mud: lives over sand and mud:
  • Observations WILD: brackish marshes of Mississippi bayou, USA (introduced) 2, Opa reservoir, Nigeria 3, Limpopo river, South Africa (introduced) 39.
• Other substrate: no data found yet.

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• Environmental enrichment and aggression:
  • LAB: pairs of size-matched male JUVENILES in 40 x 24 x 20 cm 20 L tank, environmentally enriched with 1 kg of river pebbles and plastic kelp models. Higher number of bites and lateral fights than in control condition; no difference in latency to fight, duration of fights, frequency of chases, and mouth wrestles. Corresponds to hypothesis that enriched environment increases resource value which in turn prompts more intense fights 24.

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• FARM: FINGERLINGS in 75 m² 1.2 m deep earthen ponds at 20,000 IND/ha. After five months, higher weight gain (202 g versus 155 g) and better FOOD CONVERSION RATIO (1.4 versus 1.9) with added bamboo poles where periphyton grew than without substrate. Addition of substrate without effect on chlorophyll-a-concentration 40.

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• Plants: no data found yet.
• Rocks and stones: no data found yet.
• Sand and mud: no data found.
• Other cover:
  • WILD: takes refuge from predatory Nile perch (Lates niloticus) in structurally complex wetlands of lake Nabugabo (introduced) 41↶37 42↶37 43↶37 44↶37.
  • LAB, ADULTS: after two months under laboratory conditions, more females were sexually active (61-63.5% versus 51-53%) when the concrete tank had an artificial reef installed made of bricks than when the tank had a bare bottom. Percentages for a sandy bottom (10 cm layer) were in between (56.6-57.2%). Trend towards fewer but heavier oocytes in females in the reef tanks than in the bare bottom tanks, sandy tanks in between 45.
  • LAB, ADULTS: males preferred aquaria with shelter over those without, and aquaria with gravel over those without. In aquaria with shelter and gravel and bare bottom compartment, males preferred the gravel compartment on the first day and were indifferent between shelter, gravel, and bare bottom compartments on the following days 46.

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• Observations: 2.0±0.0 se 32.

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• Omnivorous D2. The fishery that provides fish meal and fish oil has two major impacts:
  1. It contributes considerably to overfishing, as it accounts for 1/4 47 or even 1/3 48 of the world catch volume.
  2. It challenges animal welfare, because in the face of 450-1,000 MILLIARD wild fishes caught worldwide each year to be processed into fish meal or fish oil 49, the individual fish gets overlooked and, thus, suffering increases at rearing, live marketing, and slaughtering levels 50.

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• Food items: either predominantly herbivorous, mainly Phytoplankton (algae, epiphytic diatoms) and bottom debris, or omnivorous, mainly (macro)invertebrates and detritus:
  • Observations herbivorous WILD: 53↶37 54↶37 55↶37; lake Nyamusingiri and lake Kyasanduka, Uganda (introduced) 36, Ero reservoir, Nigeria (introduced) 38, Xochimilco wetland, Mexico (introduced) 1, Limpopo river, South Africa (introduced) 39.
  • Observations omnivorous WILD: 56↶37 57↶37; lake Nabugabo, Uganda (introduced) 37, Mississippi bayou, USA (introduced) 58.
• Food items and habitat:
  • WILD: mainly detritus in open water and wetland ecotone, mainly insects (chironomid and ephemeropteran larvae) and plant material in forest edge. Greater diet richness in forest edge and wetland ecotone than open water. In wetland ecotone, highest percentage of Oligochaetes and Phytoplankton: blue green algae Microcystis and Anabaena: lake Nabugabo, Uganda (introduced) 37.
• Food items and life stages:
  • WILD: JUVENILES mainly animals and plants, ADULTS mainly Phytoplankton: lake George, Uganda 55↶37.
  • WILD: JUVENILES mainly detritus and Phytoplankton, ADULTS mainly detritus, insects, and plants: lake Nabugabo, Uganda (introduced) 37.
  • WILD: JUVENILES mainly phytoplankton, ADULTS from 21 cm on mainly detritus and unidentified green spheres: lake Nyamusingiri and lake Kyasanduka, Uganda (introduced) 36.
• Food preference: no data found yet.
• Food partitioning:
  • WILD: food items differ given presence of Lates niloticus: mainly detritus and insects given introduced L. niloticus, mainly Phytoplankton (1. Chlorophyta, mainly Scenedesmus, and 2. Cyanophyta, mainly Microcystis) and detritus without L. niloticus 57↶37 36 37.
  • WILD: great overlap in diet of introduced O. niloticus and indigenous O. mossambicus but difference in isotopic composition indicates food partitioning 39.
• Prey density: no data found yet.
• Prey size selectivity: no data found yet.
• Particle size:
  • LAB, JUVENILES: optimum particle size relative to mouth width for fastest growth: 28 to 25% mouth width from 3 to 20 g fish weight. Particle size for highest food intake smaller than that for fastest growth 59.

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• WILD: depending on diet either filter feeding (Phytoplankton) or active pursuit and pecking (animals) 55↶37.
• High percentage of mud, detritus, debris, sand grains in stomach indicates that species is bottom grazer:
  • Observations WILD: ADULTS: Ero reservoir, Nigeria (introduced) 38; Mississippi bayou, USA (introduced) 58.

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• LAB: when fed the same daily ration for 12 weeks, JUVENILES grew heavier at a low compared to high initial stocking density (0.2 kg/m³ versus 0.6 kg/m³) and at a high compared to low feeding frequency (3 or 4 times/d versus 2 times/d). Increasing stocking density increased the variation in body weight for groups of 2 feedings/d but decreased the body weight variation at 3 or 4 feedings/d 60.

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• LAB: in groups of 15 ADULTS, increased plasma cortisol levels even 1 h after feeding (ca 60 ng/mL) indicate food competition. No plasma cortisol increase in single-held ADULTS after feeding and in unfed ADULTS in groups of 15 (ca 10-20 ng/mL) 25.

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• Daily rhythm:
  • LAB, FRY: mainly diurnal feeding pattern with peaks at dawn and dusk 4.
  • LAB, ADULTS: large inter-individual differences in activity rhythms:
    a) When held under a cycle of "12 h light and 12 h dark", four of 12 males were diurnal, displaying average locomotor activity of 70.3% during the photophase, five males were nocturnal, displaying average locomotor activity of 64.4% during the scotophase, three males were arrhythmic.
    b) When held in complete darkness, six of 12 males developed locomotor activity free-running rhythms of 24.1 hours on average.
    c) When held under pulses of 45 min light and 45 min dark, seven of 12 males developed locomotor activity free-running rhythms of 23.9 hours on average.
    d) When shifted to a cycle of "12 h dark and 12 h light", three males changed their locomotor activity to match the new photoscope immediately, four did so gradually, others did not resynchronise at all.
    e) When held under a cycle of "12 h light and 12 h dark", five of 11 females were diurnal, displaying average locomotor activity of 74.4% during the photophase, one female was nocturnal, displaying average locomotor activity of 68.0% during the scotophase, five females were arrhythmic. In nine of 10 females that spawned during the experiment, reproductive activity decreased the locomotor activity prior, during, and/or after spawning 5.
• Nocturnal activity: ➝ Daily rhythm.
• Phototaxis: no data found yet.

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• LAB: JUVENILES under 12 h PHOTOPERIOD had lower mortality (20% versus 40% versus 76.7%) and lower growth than under 24 h PHOTOPERIOD and 24 h scotopheriod. Under 24 h scotoperiod, JUVENILES displayed injuries on their bodies as well as suppressed behaviour and swimming activity compared to the other conditions 61.

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• LAB: groups of three similar-sized male ADULTS in 60 x 60 x 40 cm 140 L aquaria. Tendency of fewer aggression under low light intensity of 280.8 lux than under high intensity of 1,394.1 lux. No effect of light intensity on social hierarchy 22.

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• LAB: single individuals in 12 x 20 x 30 cm aquaria under 12 hours white, blue, or yellow light (ca 50 lux each) per day (06:00-18:00 h) for seven days. No difference in ventilatory frequency (85.7-94.7 opercular or buccal movements/min) 29.

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• LAB: individual ADULTS in 40 x 25 x 20 cm 15 L glass aquaria covered with gelatin filter of different colours: blue 434.5 nm, violet 430.0 nm, red 609.7 nm, green 525.2 nm, yellow 545.2 nm. After 30 days, no difference in weight 62.
• LAB: groups of four similar-sized ADULTS in 60 x 40 x 30 cm 50 L glass aquaria. After 30 days, weight differences within groups under each light colour except yellow light. Highest variation under red light, lowest under yellow light, other light colours in between. No difference between individuals of the same size category under the different light colours 62.

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• Standard temperature range:
  • Observations WILD: 16-29 °C: Mississippi bayou, USA (introduced) 2, 24-25 °C: lake Nabugabo, Uganda (introduced) 37.
• Optimum range for survival: 22-34 °C:
  • Observations FARM, FRY: >26 °C 63.
  • Observations LAB, FRY: 28-30 °C 11, 20 day old FRY: 22-34 °C 64, first-feeding FRY: 32-34 °C 64.
• Temperature preference: no data found yet.
• For temperature and spawning ➝ D7.

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• Lower and upper lethal limits:
  • FARM: eggs died within 24 hours when exposed to water temperatures of ≤17 °C and 39.5 °C directly after fertilisation, best hatching rates at 25-30 °C with peak at 28 °C. Eggs reared at 28 °C for 48 hours after fertilisation hatched best at 23.5-32 °C with peak at 28 °C. The higher the temperature the faster morphological differentiation and hatching 11.
  • Range of temperature tolerance: 8-42 °C 65.
• High temperatures: contradictory results on influence of elevated water temperatures for 21 days on survival of first-feeding FRY:
  a) No influence on survival: LAB: 34 or 36 °C water compared to 27 °C rearing temperature 66.
  b) Lower survival: LAB: putative all-female population: 62.7% at 36.5 °C versus 71.9% at 27.9 °C, putative all-male (XY and YY each) population of temperature-sensitive (Egypt-Swansea) strain: XY males: 70.3% at 37.1 °C versus 90.7% at 30.1 °C, YY males: 53.0% at 36.5 °C versus 90.7% at 29.7 °C 67; 28 days treatment: 75% at 36.5 °C versus 93.3% at 32 °C 64.
  c) Higher survival: LAB: putative all-male (XY) population: 59.5% at 36.5 °C versus 35.1% at 27.9 °C, putative all-female population of temperature-sensitive (Egypt-Swansea) strain: 75.0% at 37.5 °C versus 58.3% in 29.6 °C 67.

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• Temperature must exceed: no data found yet.
• Temperature must not go beyond: no data found yet.
• Optimal temperature for growth:
  • LAB: 20 day old FRY grew better when reared in 30 °C water than in 26 °C, 34 °C, and 22 °C. Higher food intake in 30 °C water than in 26 °C, 34 °C, or 22 °C 64.

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• Observations WILD: 7.6 mg/L at surface, 0 mg/L in 4 m depth: lake Nyamusingiri, Uganda (introduced) 36, 12.0 m/L at surface, 0.1 mg/L in 2 m depth: lake Kyasanduka, Uganda (introduced) 36, 6.5 mg/L: lake Nabugabo, Uganda (introduced) 37.
• Observations FARM, JUVENILES: dissolved oxygen preferably >4 mg/L to prevent furunculosis. Alternatively, decrease density in cages 63.

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• Salinity tolerance:
  • Natural and introduced distribution in fresh water or brackish water at most D8 D9.
• Standard salinity range: no data found yet.

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• Lower and upper lethal limits:
  • LAB: no difference in survival of first-feeding FRY reared at salinities of 0-26.8‰ for 21 days, lower survival in one sample at 0‰ because of bacterial infection 67.
  • LAB: some JUVENILES survived 35‰ salinity for up to six weeks when gradually exposed to increasing salinity beginning at 15 days old. Mortality in intermediate levels of up to 50‰ in first days after transfer 68.
• Salinity change and stress: no data found yet.

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• Standard pH range:
  • Observations WILD: pH 7.9-8.0: lake Nyamusingiri and lake Kyasanduka, Uganda (introduced) 36.
• pH preference: no data found yet.

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• Standard turbidity range: no data found yet.
• Secchi depth (water transparency): 0.2-0.8 m:
  • Observations WILD: 0.2 m: lake Kyasanduka, Uganda (introduced) 36, 0.8 m lake Nyamusingiri, Uganda (introduced) 36.
  • WILD: 0.7-0.8 m: lake Nabugabo, Uganda (introduced), with higher abundance at lower water transparency – protection from Lates niloticus 37?

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• Observations: 69↶32 70↶32.

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• Depth range in the wild:
  • Observations WILD: 2 m: lake Kyasanduka, Uganda (introduced) 36, 4.9 m: lake Nyamusingiri, Uganda (introduced) 36, 0.75-6.4 m, Opa reservoir, Nigeria 3, 20 m 71↶32.
  • WILD: JUVENILES and smaller ADULTS more abundant in the forest and wetland ecotone habitat than in the open-water habitat 55↶37 57↶37 72↶37 37.
• Depth in cages or tanks: no data found yet.
• Depth preference: no data found yet.
• Depth and daily rhythm: no data found yet.
• Depth and low temperatures: no data found yet.
• Depth and high temperatures: no data found yet.
• Position in habitat and age: no data found yet.
• Depth and light intensity: no data found yet.
• Depth and noise: no data found yet.
• Depth and threat: no data found yet.

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• Observations time from fertilisation until hatching LAB: 90-102 hours 11, average 5 days 73.
• Observations size: 1.5 mm 33↶32; WILD: average 2.47±0.02 mm: Opa reservoir, Nigeria 3.
• Observations weight: no data found yet.

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• Observations age at yolk sac absorption LAB: day 9-12 11, day 6-8 73.
• Observations TOTAL LENGTH: 4 mm 33↶32; LAB: 4.5 mm 11, 4.9±0.1 mm 73.
• Observations weight LAB: 1.7-3.7 mg 11.

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• Observations age and TOTAL LENGTH at beginning of exogenous feeding LAB: 4 days at 20 °C and 5-6 days at 28 °C 11, 5-8 days, 9.9 mm 73.
• Observations pigmentation of the eyes, swim bladder inflation LAB: 5-6 days 11, 1-2 days 73.
• Observations weight: no data found yet.

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• Fingerlings: FRY with fully developed scales and working fins, the size of a finger, 12.6 cm, 1.8-40.3 g:
  • Observations TOTAL LENGTH and weight FARM: 12.6 cm, 40.3 g 75, 16.3-16.5 g 76, 1.8 g 40.
  • Observations weight LAB: 20 g 77.
• Juveniles: fully developed to beginning of maturity, 7.6-9.4 cm, 5.3-25.5 g:
  • Observations TOTAL LENGTH and weight LAB: 8.7-9.4 cm and 21.5-25.5 g 14, average 5.3-6.8 g 78, average 7.6 cm and 12.8 g 27.
• Sexual maturity: 3-7 months depending on temperature (although it has also been reported at 50-60 days), 7-37 cm, 16-90 g:
  • Observations TOTAL LENGTH WILD: 17-37 cm 79↶11, length at maturity for 50%: 12-15 cm: lake Nyamusingiri and lake Kyasanduka, Uganda (introduced) 36, females: 8-35 cm: Mississippi bayou, USA (introduced) 2, length at maturity for 50% females: 11.3 cm: Mississippi bayou, USA (introduced) 2.
  • Observations age, TOTAL LENGTH, and weight LAB: 3-6 months, 30 g 33↶32, 5-7 months, 50-60 days, 7-12 cm, ca 16-90 g 11, average: 18.6 cm, range: 10-28 cm 32.

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• Observations age: ➝ D10.
• Observations TOTAL LENGTH and weight WILD: 28-56 cm, 360-2,940 g: Nyanza Gulf of lake Victoria, Kenya (introduced) 35, 4,300 g 80↶32, 22-26 cm: lake Nyamusingiri, Uganda (introduced) 36, 22-29.5 cm: lake Kyasanduka, Uganda (introduced) 36, males: 43 cm, females: 15-35 cm, Mississippi bayou, USA (introduced) 2, 18-37.7 cm, 110-969 g: Opa reservoir, Nigeria 3.
• Observations TOTAL LENGTH and weight LAB: 7.3-11.1 cm 28, 14.4 cm 20, 663 g 81, 7.8 cm, 17.2 g, 12.8 cm, 62.9 g 62, male 12.9 cm, 67 g, female 12.3 cm, 55.8 g 10, 493.3 g 82.

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• Sex and temperature manipulation: mixed effects of elevated temperatures:
  a) increase in portion of males: transfer to elevated water temperature after first feeding increases portion of male FRY compared to control rearing temperature:
  • Observations LAB: 81% males at 36 °C versus 53% at 27 °C 66, putative all-female population: 0-89.6% males at 36.5 °C versus 0-36.8% at 27.9 °C, trend among putative all-female population of temperature-sensitive (Egypt-Swansea) strain: 37.3% at 37.5 °C versus 20.2% at 29.6 °C 67, average 61.4-78.4% at 36 °C versus 49.9-53.1% at 28 °C, no further increase at 38 °C 83, 64.2-80.0% at 36.5-36.8 °C versus 43.6-56.7% at 19.2-34.4 °C 64.
  • LAB, FRY: temperature manipulation less effective at later transfer (from 15 days post fertilisation on) 66. Duration of 10 days under elevated temperature sufficient 66 83. Other influencing factors: less effective with interbred than with purebred individuals 83, effectiveness heritable 83, effectiveness varies with breeding pairs, as both partners influence sex ratio 83.
  b) decrease in portion of males:
  • LAB, FRY: elevated water temperature decreased portion of males in all-male YY populations of temperature-sensitive (Egypt-Swansea) strain compared to control rearing temperature: 7.6% at 37.5 °C versus 100% at 29.7 °C, 33.3-90.8% at 36.5 °C versus 100% at 28.8 °C 67.
• Sex and hormone treatment: highest portion of male FRY and concurrently highest weight gain and survival at androgen treatment of 40 mg/kg 17-alpha-methyltestosterone and 2,000 IND/m³ stocking density:
  • FARM:
    a) FRY at either 2,000 IND/m³ in hapa net versus 5,000 IND/m³ in concrete tank. Treatment after first feeding with 40 mg/kg of the androgen 17-alpha-methyltestosterone increased portion of male FRY compared to control (average 95.4-98.4% versus 52.3-53.3%) independent of stocking density. Higher weight gain at low density (221.4 mg versus 74.4 mg).
    b) FRY in hapa nets at either high densities of 6,000 or 10,000 IND/m³ or low density of 2,000 IND/m³. Treatment with 60 mg/kg 17-alpha-methyltestosterone increased portion of male FRY more at high stocking densities compared to control, lower at low stocking density (average 96.7-99.4% verus 91.2% at versus 55.2% control). Lower survival (68.9-76.1% versus 92.2%) and lower weight gain (33.5-56.2 mg versus 138.4 mg) than at low density 84.
  • FARM: FRY in earthen ponds at either high densities of 200 or 260 IND/m² or low density of 75 IND/m². Treatment with 60 mg/kg 17-alpha-methyltestosterone increased portion of male FRY more at high stocking densities than at low stocking density (average 96.5-98.2% versus 87.0-94.0%) 85.
  • LAB: treatment after first feeding with 40 mg/kg of the androgen 17-alpha-methyltestosterone increased portion of male FRY compared to control (average 93.3% versus 53.1%) 86.
• Sex and genetic manipulation: breeding programme for large-scale application in aquaculture:
  1. Crossing XY delta females (i.e., males sex reversed using 1,000 mg/kg of the estrogen diethylstilbestrol) with XY males and progeny testing the resulting males yields YY males,
  2. crossing XY delta females with YY males and progeny testing the resulting males yields a higher proportion of YY males,
  3. crossing XY delta females with YY males and progeny testing the resulting females yields YY delta females,
  4. crossing YY delta females with YY males and progeny testing the resulting males and females yields an average 98.9-100% males 87.
• Sex and other manipulation: salinity
  • LAB: no influence of salinity (0-26.8‰) on sex of first-feeding FRY of putative all-female population 67.

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• Observations WILD: 1:1: lake Nyamusingiri and lake Kyasanduka, Uganda (introduced) 36, 1.0:0.8: Opa reservoir, Nigeria 3, 2.08:1.0: Nyanza Gulf of lake Victoria, Kenya (introduced) 35.

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• Observations bimodal pattern LAB, JUVENILES: males developed faster than females 73.
• Beginning of noticeable size difference: at 2-5 months:
  • Observations FARM: 2-5 months 63.
  • Observations LAB: at 2 months, YY males in monosex population heavier than XX females in monosex population, at 3 months, additionally in 50-50 mixed population 88.
  • LAB: using a self-feeder, although food intake was similar, 4 month old male FRY gained more weight over 41 days than females in mixed populations (average 58.4 g versus 40.1-42.8 g), most in male monosex populations (average 70.1 g). Females gained more weight when in monosex (average 42.8 g versus 40.1 g) than in mixed populations 4.
  • LAB: after ca 130 days ad libitum feeding, male first-feeding FRY gained more weight than females a) in XY monosex population (versus females in 17% males and 83% females population) and b) in mixed populations (75% XY and 25% XX, 50% YY and 50% XY). Males grew better in a XY monosex population than in a YY monosex population, XX delta monosex population (i.e., males sex reversed using 30 mg/kg of the androgen 17-alpha-methyltestosterone) in between. Females gained most weight when proportion of population was 25% than when higher (50, 75, 100%), even surmounting that of YY males in population 88.

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• Growth and size-grading:
  • LAB, JUVENILES: size-grading at 8 weeks (stocking density 0.2 kg/m³) did not reduce size variation but established it anew in small, medium, and large size groups. In contrast, size variation in mixed groups decreased. Higher specific growth rate (log weight difference given time) at week 10 in mixed groups than size-graded groups 60.
• Growth, size-grading, and density:
  • LAB: JUVENILES in a low initial size variability (0 versus 58%) and low density group (2.5 versus 10 kg/m³) grew heavier after 16 days than at high size variability and high density. After 30 days, high initial size variability did not influence weight anymore: weight of JUVENILES in low density groups was higher than weight of JUVENILES in high density groups. Coefficients of variance in both low and both high density groups converged by day 30 with variance in low density groups being lower (ca 15 versus 45%) than in high density groups 18.

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• Growth and age of female:
  • LAB: eggs from 1+ and 2+ years females were larger than from 0+ females. LARVAE grew larger and survived longer the larger the egg (i.e., yolk sac) or the older the female respectively. A higher number of FRY were able to feed exogenously and survive longer the older the female (50% survival at 16 and 17.5 days versus 13.5 days). When adding exogenous feed, the initial difference in growth rates of FRY ceased by day 60 11.
• Growth in polyculture:
  • FARM: five months of polyculture of genetically improved O. niloticus strain with freshwater prawn Macrobrachium rosenbergii at 20,000 IND/ha of FINGERLINGS or POST-LARVAE did not affect survival or weight gain 40.
  • FARM: FINGERLINGS in 150 m² (1.5 m deep) earthen ponds either stocked under monoculture or polyculture at 3:1 ratio with Clarias gariepinus at low (30,000 IND/ha), medium (60,000 IND/ha), or high density (90,000 IND/ha). C. gariepinus were deliberately stocked 30 days after O. niloticus (5 g mean weight) so that these were too big for C. gariepinus to prey on. After 240 days, higher growth of O. niloticus under poly- than monoculture (75,460 g weight gain versus 66,879 g), specifically under low stocking density (204.7 g versus 141.6 g under high, 132 g under medium stocking density). Also, higher survival (98.1% versus 86.6-89.3%) and higher specific growth rate (1.6% versus 1.4%) but higher FOOD CONVERSION RATIO (3.5 versus 2.6-3.1) under low density. In C. gariepinus, higher weight gain under low than medium and high stocking density (579.5 g versus 519.2 under medium, 341.3 under high density). Also, higher survival (97.9% versus 89.5-96.6%) and higher specific growth rate (2.2% versus 2% in high density) but FOOD CONVERSION RATIO (3.5 versus 2.6 under high density). Results indicate that polyculture with C. gariepinus is beneficial for O. niloticus probably because C. gariepinus preys on O. niloticus juveniles that would otherwise compete for food with adults 89.

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• Nest building and substrate:
  • ADULTS spawn in firm sand in 0.6-2 m water depth 33↶32.
  • LAB, ADULTS: males and females built nests in aquaria with 3 cm gravel layer. Average 0.3-0.6 nests per individual of average 85-311 cm² area 9.
  • LAB, ADULTS: groups of one male, two females in 60 x 60 x 40 cm glass aquaria divided into four compartments with 3 cm substrate: sand, mixture of sand and bivalve shells, stones, glass plate (no substrate). Before nesting, females and males did not prefer either compartment but explored all substrata by nipping with mouth. Males nested within five days, preferred sand over sand-shell-mixture, did not nest in other compartments 10.
• Nest building and water velocity: no data found yet.
• Nest building and water depth: no data found yet.
• Nest building: no data found yet.

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• Nest building and light colour:
  • LAB, ADULTS: males moved larger mass for nest building (average 311 versus 131 g) and built wider nests (average 208 versus 98 cm² area) under blue than under white light (100-120 lux) in aquaria with 2 cm gravel layer 6.
• Nest building and olfaction:
  • LAB, ADULTS: anosmic males built fewer and smaller nests than males with intact sense of olfaction in aquaria with 2 cm gravel layer. Not being able to smell did not influence spermatogenesis and aggressive, foraging, and courtship behaviour like nudging, leading, and circling. Olfactory input seems to influence motivation – but not consummation – of male reproductive behaviour 7.
• Nest building and dominance:
  • LAB, ADULTS: in groups of two males and three females, the dominant males built nests and defended them against male and female conspecifics. The higher the investment in nest building (weight of gravel displaced per body weight), the higher the spawning frequency and the more frequent female nest visits 8.

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• Attraction and body colour:
  • WILD: mature males and females changed colour on ventral surface and especially around pharyngeal region to reddish-brown: Opa reservoir, Nigeria 3.
• Signals of maturity:
  • LAB, ADULTS: nest building and swollen urogenital papilla in females signalled readiness to spawn 86.

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• Courtship sequence:
  • LAB, ADULTS: male gently bit or nudged the female near the anal region, swam ostentatiously in front of her to lead her to the spawning site, quivered sideways and circled around the female 7.
  • LAB, ADULTS: increased male and female undulation behaviour (component of courtship) when visual or visual and chemical communication between male and female possible than when chemical communication alone or isolation 9.
• Courtship duration:
  • Courtship lasts several hours 33↶32.

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• Rather K selection, but may convert to r selection under aquaculture conditions 90.

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• Monogamy:
  • WILD, ADULTS: temporary pair bond between ripe female and nesting male 33↶11.
• Polygyny:
  • Observations: 33↶32.
• Polyandry:
  • Observations: 91↶32.
• Diverse mating systems:
  • LAB, ADULTS: 25 females and 12 males in 8 x 2 x 1 m³ hapa nets mated. 21.05% of fry from mating between single male and single female (monogamy), in 46.05% up to four males fertilised single batch of eggs (polyandry), in 10-30% a single male fertilised eggs from multiple mothers (polygyny), in 25% of batches multiple males fertilised eggs from multiple females (polygamy) 92.

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• Spawning substrate:
  • LAB, ADULTS: spawning frequency and latency independent of substrate in glass aquaria 8.
• Spawning season: several yearly spawnings every 20-90 days:
  • Observations WILD: 30-90 days: Mississippi bayou, USA (introduced) 2.
  • Observations FARM: 21 days 93, 40-90 days 63.
  • Observations LAB: 20-36 days 11.
  • For spawning frequency and nest building and dominance ➝ D4.
• Spawning (day)time: no data found yet.
• Spawning temperature:
  • Reproduction occurs only at temperatures >20 °C 33↶32.
• Spawning salinity: no data found yet.
• Spawning and water velocity: no data found yet.
• Spawning depth: no data found yet.
• Spawning density: no data found yet.

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• Male:female ratio resulting in spawning: 1:1-1:10:
  • Observations FARM, ADULTS: 1:4 93, 1:7 93, 1:10 93.
  • Observations LAB, ADULTS: 1:1 86 87 9, 2:3 8 or 1:3 11 63 87 45 17.
• Composition of broodstock: no data found yet.

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• Spawning sequence: no data found yet.
• Spawning duration:
  • 45-120 min 33↶11.

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• Spawning and dominance:
  • LAB, ADULTS: among groups of three similar-sized females, the dominant female did not have priority mating when one male was added to the aquaria, but was first mating in four of eight cases, the beta-female in three of eight cases 17.
  • LAB, ADULTS: spawning only in dominant males 8.
• Spawning and communication:
  • LAB, ADULTS: spawning only when visual or visual and chemical communication between male and female possible 9.

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• Number of batches:
  • WILD, ADULTS: judging by five or more stages of oocytes in disected ovary, authors conclude that eggs are shed in batches 35.
  • WILD, ADULTS: largest oocytes of ≥1 mm form batch in disected ovary 2.
• Fecundity per batch:
  • Observations absolute fecundity WILD (disection studies), ADULTS: 864-6,316 eggs 35, 30-2,603 eggs 2, 73-1,810 eggs of all stages per female 3.
  • Observations absolute fecundity FARM, ADULTS: depending on hatchery system, stocking density, and sex ratio, average 2.2-8.8 seeds (eggs or FRY) per spawner per day with peaks in February-April and July-September 93, 62-183 FRY per female per month 63.
  • Female sheds eggs in batches of 20-50 eggs, male sheds sperms over the site 33↶11.
  • Observations LAB, ADULTS: 121-2,030 eggs 11.
  • Observations relative fecundity WILD (disection study), ADULTS: 0.3-26.8 eggs/g body weight 3.

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• Number of spawns:
  • LAB, ADULTS: spawning in males 2-4 times a day. The higher the spawning frequency, the less fertilised eggs 11.
• Fecundity per spawn: no data found yet.

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• Fecundity and aquaculture system:
  • FARM, ADULTS: higher seed production (eggs or FRY) in concrete tanks than hapa nets, no difference between male:female ratios of 1:4, 1:7, 1:10, no difference between stocking densities of male:female 4:16, 7:28, 10:40 93.
• Fecundity and age:
  • LAB, ADULTS: the higher the female's age, weight, and length the higher the total fecundity (number of eggs per spawn). The older the female the higher the relative fecundity (number of eggs per kg weight) 11.

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• Breeding type: mouthbreeder:
  • Observations number of eggs: ≤200 eggs 33↶32; WILD: 39-241 eggs 3.
  • Observations duration of carrying: ca 1 week 33↶32; LAB: 11-18 days 11.
  • Observations carrying FRY WILD: Mississippi bayou, USA (introduced) 2, Opa reservoir, Nigeria 3.
• Churning:
  • LAB, ADULTS: females' churning of the clutch in their mouth decreased from 95-105 times/min after spawning to 20-30 times/min on day 3 and occasional churning (3-8 times/min) on days 5-10 11.
• Artificial incubation versus natural rearing:
  • LAB, ADULTS: no difference in hatchability and survival of FRY between artificial incubation and natural rearing in first 72 hours 11.
  • LAB, ADULTS: most of loss or damage to eggs or FRY in buccal cavity happened on days 5-8 after spawning, cumulating to 25% of clutch 11.

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• Mouthbreeding and light colour:
  • LAB, ADULTS: higher proportion of mouthbreeding under blue than under white light 6.
• Rearing container:
  • Eggs hatched at a higher rate (91.6% versus 74.6%) and survived with higher probability (92.3% versus 80.7%) in round-bottom than conical hatching jars, suggesting mechanical stress through friction between eggs and between eggs and container as major influence 11.

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• LAB: ADULTS had sensitivity peaks at short (380-420 nm, 440-480 nm), middle (500-600 nm), and long wavelengths (600-680 nm) 94.

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• Olfaction and risk perception:
  • LAB: cortisol levels of mixed-sex JUVENILES that were exposed to water from stressed conspecifics were higher than those of a control group for at least 2 h. Cortisol levels after 2 h were similar to the stressed conspecifics. After 8 h, the levels were back to normal 95.
• For olfaction and nest building ➝ D4.

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• Hearing type:
  • LAB, ADULTS: hearing GENERALIST 96.
• Hearing spectrum:
  • LAB: ADULTS did not react at the onset and did not avoid the area around the source of white noise of 0.1-10 kHz at 164-170 dB re µPa. Auditory brainstem responses to noise at 100-800 Hz, auditory thresholds at 90-130 dB re µPa 96.

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• LAB, ADULTS: no hearing loss when exposed to noise at 100-800 Hz for seven days. When exposed to noise for 28 days, only at 800 Hz (not below) auditory threshold 10 dB higher than control, indicating slight hearing loss 96.

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• LAB: female ADULTS in 140 L tanks half covered with black plastic had caudoventral corner of tailfin clipped. Higher activity, predominantly random swimming, compared to untreated individuals and individuals, which were just caught by net and applied pressure to the tailfin, for at least 6 h after clipping. Back to control levels at next observation 24 h after clipping. Higher cortisol levels compared to untreated individuals at 6 h after clipping (334.6 nM versus 24.6 nM), back at control levels at 24 h after clipping. No difference in glucose and lactate levels. Decrease of mucus cells at 1 h after clipping indicate excretion of mucus and discriminates between pain from tail clip and stress from handling without clipping 99.

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• LAB, ADULTS: when another male entered the territory, nesting males released pulse trains of 2-4 pulses of 57.4 Hz, each pulse lasting 114 ms and comprising a high pitched part and broader peaks, by moving the scapular and pelvic girdles backward while simultaneously moving the second pterygiophore of the anal fin forward. This compresses the rib cage and the swim bladder. They achieve the movement by contracting sonic muscles close to the swim bladder which results in resonance. Deflating the swim bladder artificially weakened the sound pressure but maintained duration and frequency 12.

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• LAB, ADULTS: sounds by the pharyngeal jaws of a frequency of 2,868.1 Hz lasted 22.9 ms 12.

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• LAB: 27 individuals of 2 months old JUVENILES (2 cm length) built a shoal 13. 12 days old JUVENILES (12 mm length) built shoals with density of 10 to 100 individuals 13, amounting to ca 2-20 g shoal weight (estimate by FishEthoBase).

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• FARM, FRY: survival >75% at density of 1,000-3,000 IND/m³ during two month growing period, decreasing survival at increasing density 63.
• LAB: FINGERLINGS in 100 L tanks with 30% daily water exchange at densities 1, 2, 5, 10 IND/tank. After 60 days, higher plasma cortisol level in 10 FINGERLINGS group compared to single FINGERLINGS or pair tanks (ca 45 ng/mL versus 10 ng/mL); 5 FINGERLINGS groups in between. Lower weight gain in 5 and 10 FINGERLINGS groups (ca 11 versus 14 g) compared to single FINGERLINGS and pair tanks indicating chronic stress by overcrowding 77.

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• Inverse relation:
  • FARM, FRY: higher weight gain (average 419.0 mg versus 278.3 mg versus 92.1 mg) in ponds with stocking density 500 IND/m³ than hapa nets with 2,000 IND/m³ and concrete tanks with 5,000 IND/m³ 84.
  • FARM: FINGERLINGS in 1 m deep 100 m² stagnant earthen ponds at 1 IND/m² (ca 0.02 kg/m²), 3 IND/m² (ca 0.05 kg/m²), or 5 IND/m² (ca 0.08 kg/m²). After 90 days, no difference in survival (74-78.9%), but higher final weight (108.3-115.1 g versus 89.5 g), higher daily weight gain (1-1.1 g versus 0.8 g), and lower FOOD CONVERSION RATIO (1.3 versus 1.6) in low and middle stocking densities compared to high density. Probably due to lower dissolved oxygen (3.2 versus 5.3 mg/L) in high compared to low density; middle density in between. Probably higher feeding pressure in high density condition indicated by higher Secchi disc (51.3 versus 35 cm), lower chlorophyll a (11.6 versus 17.4 µg/L), and lower Zooplankton (561 versus 906) in high than low stocking density; middle density in between 76.
  • For stocking density, growth, and size-grading ➝ D19.
• No effect:
  • FARM: all-male FINGERLINGS in 2.5 x 1.5 x 1.1 m 3.75 m³ concrete outdoor tanks with water flow rate of 1 L/min/kg at densities 16 IND/m³ (ca 0.6 kg/m³), 32 IND/m³ (ca 1.3 kg/m³), 42.5 IND/m³ (ca 1.7 kg/m³). After 164 days, no difference in survival (95.9-99.2%), final weight (322-336 g), daily weight gain (1.7-1.8 g), and FOOD CONVERSION RATIO (1.8-2) 75.

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• Hierarchy and group size: in small groups, individuals establish linear hierarchy, although not always:
  • Observations linear hierarchy LAB, JUVENILES: of four males, one became dominant, two were of secondary dominance, and the fourth became subordinate 18.
  • Observations linear hierarchy LAB, ADULTS: between two similar-sized males 16, of three similar-sized females, one became dominant, the others beta and gamma subordinate 17, between two males 7, of two males and three females, one male became dominant 8, of three similar-sized males, one became dominant, one intermediate, one subordinate 22.
  • Observations exception LAB: pairs of size-matched FINGERLINGS in 100 L tanks separated by biological filter. After 60 days, no dominance hierarchies probably due to huge space available and establishment of territories in opposite corners 77. ADULTS: in seven of 10 groups of two males, one male became dominant 15.
• Establishing hierarchy: after 25-150 min:
  • LAB: in pairs of size-matched male JUVENILES in 40 x 24 x 20 cm 20 L tank, fighting began after 4 min on average for ca 25 min on average 24.
  • LAB: among groups of two similar-sized male ADULTS, hierarchy was established via fightings in about 2.5 hours. In the initial 5 min of pairing, both males did not differ in their colour pattern and the number of attacks initiated. Fightings increased in aggressiveness. Dominance relationship at a second pairing, 14 days after the first pairing, was again fought out and remained the same 16.
  • LAB: groups of three similar-sized male ADULTS in 60 x 60 x 40 cm 140 L aquaria. Hierarchy had established at first observation session at day 3. Tendency of decreasing frequency of aggression after seven days 22.

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• Features of dominance:
  a) Dominant individual has lighter body and eye colour than subordinate:
  • Observations body colour LAB, JUVENILES: lighter body colour 21 24.
  • Observations body colour LAB, ADULTS: silver colouration with black stripes 16, pinkish-red colour 7, lighter body colour 20 8.
  • Observations eye colour LAB, ADULTS: decreased percentage iris and sclera darkening compared to basal condition 15, lighter eye colour 20.
  b) Dominant individual raises dorsal fin:
  • Observations LAB: JUVENILES 18; ADULTS 17.
  c) Dominant individual stays in the confrontation area:
  • Observations LAB: JUVENILES 18; ADULTS 15.
  d) Dominant individual holds the spawning site:
  • Observations LAB: ADULTS 7.
  e) Dominant individual chases and (occasionally) attacks the conspecific, wins more fights than the subordinate(s):
  • Observations chases and attacks LAB: JUVENILES: 18 21 24 23; ADULTS: 16 15 17 8 22.
  • Observations more wins LAB: JUVENILES: 18, proportion of attacks given all interactions: dominant JUVENILES 0.85-0.87, subordinate 0.17-0.20 24; ADULTS 17.
• Hierarchy and territoriality: the resident becomes dominant over the intruder:
  • Observations LAB, ADULTS: in six of seven groups of two males 15, larger male became resident over smaller male intruder 19 20.
• Hierarchy and sex:
  • LAB: no difference in fighting latency, fighting duration, and frequency of aggressive interactions between pairs of immature male FRY, pairs of immature females, and mixed-sex pairs. No effect of sex on dominance: of 30 mixed-sex pairs, 17 males and 13 females became dominant 23.
• For dominance and...
  ...nest building ➝ D4,
  ...spawning ➝ D18.

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• Features of subordination:
  a) Subordinate individual has darker body colour than dominant:
  • Observations LAB, JUVENILES: darker body colour 21 24.
  • Observations LAB, ADULTS: dark grey colouration without stripes 16 17, dark “zebra-like” pigmentation 7.
  b) Subordinate ADULTS has darker eye colour than dominant:
  • Observations LAB, ADULTS: increased percentage iris and sclera darkening compared to basal condition 15 17, darker eyes than dominant males (>80% versus 25%) 15.
  • LAB, ADULTS: both eye colour effects (difference to basal condition, difference between dominant and subordinate male) occurred only in pairs with 1-111 attacks (first and second quartile), not in pairs with 112-168 attacks (third and fourth quartile), although they might have occurred in high-attack pairs after the end of the observation period. This indicates that the eye colour changes only after establishment of hierarchy which can take place sooner (low-attack pairs) or later (high-attack pairs) 15.
  c) Subordinate ADULTS flees attacks, does not fight back:
  • Observations LAB: fled attacks 17, did not fight back 16 17.
  d) Subordinate ADULTS withdraws the dorsal fin:
  • Observations LAB, ADULTS: 17.
  e) Subordinate individual tries to avoid contact with dominant:
  • Observations LAB: JUVENILES stayed in groups, at bottom or water surface 21.
  • Observations LAB: ADULTS swam slowly, avoided contact with the dominant male, and stayed in the opposite corner 16 or close to the aquarium surface 15 7.
• Hierarchy and stress: in pair of dominant and subordinate, the subordinate is stressed:
  • LAB, ADULTS: dominant and subordinate males did not differ in levels of plasma cortisol, glucose, triglycerides, and total protein, but these levels were higher when the individuals were paired than when they were isolated 16.
  • LAB, ADULTS: after pairing subordinate with dominant males for 60 min, the cortisol level in subordinates was increased immediately after the end of the pairing for at least 30 min. Glucose level was increased only at 30 min after the end of the pairing. Increased levels of cortisol and glucose were as high as those from groups of conspecifics receiving mild electroshocks (AC shock with 20 V, 15 mA and 100 Hz) for 60 min – without the delay in glucose level 19.
  • LAB: single male ADULTS in 60 x 28 x 31 cm 48 L glass aquaria were paired with larger male residents resulting in focal individuals becoming subordinate. After 60 min, increased ventilatory frequency (ca 72 versus 98 opercular or buccal movements/min) compared to pre-stress condition. Of nine ADULTS, eight increased and one decreased their individual ventilatory frequency 20.

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• Size-matched pairs:
  • LAB, JUVENILES: in pairs of size-matched males, dominants displayed higher frequency of a) biting on anterior (head), tail fin, median or ventral area, b) chases, and c) lateral fights. Only seldomly mouth wrestling 24.
  • LAB, ADULTS: fights to establish hierarchy between two similar-sized males (➝ D20) comprised (in descending order of frequency) approaching, tail beating, and fleeing, then mouth fighting and ramming, then chasing and biting the flanks 16.
• Non-matched pairs:
  • LAB, JUVENILES: in mixed-sex groups, dominant individuals displayed biting, ramming, cornering, and chasing of subordinate individuals and biting, ramming, and mouth-fighting of other dominant individuals 21.
  • LAB, ADULTS: non-mature males paired with larger residents for 60 min received mostly nipping of the median body (not anterior, seldomly caudal or ventral), seldomly mouth fights and chasing, no lateral fights 19.

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• Aggression and sex:
  • LAB: no difference in frequency of aggressive acts between (descending order) pairs of immature male FRY, pairs of females, and mixed-sex pairs: mainly threats and bites, then lateral and frontal display, then chases, lateral fights, and mouth wrestles 23.

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• LAB: in a group of 15, ADULTS learned to associate a conditioned stimulus (aeration off for 30 s) – in place of the unconditioned stimulus air emersion – with a conditioned response (stress = increased plasma cortisol level). Conditioning failed when the unconditioned stimulus was food – because food-competition-induced stress is milder than air-emersion-induced stress (48.9 ng/mL versus 228.4 ng/mL plasma cortisol)? 25.

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• Managing self-feeder:
  • LAB: FRY learned how to manage a self-feeder (➝ D26) 4.
• Initiating flight:
  • LAB: of 24 male JUVENILES, 22 learned to associate a conditioned stimulus (water off for 20 s) – in place of the unconditioned stimulus confinement stress – to initiate flight response. Latency to escape decreased from 513 s on day 1 to <30 s on day 7. JUVENILES avoided the aquarium department where confinement took place or took longer to return there compared to conspecifics only experiencing “water off” respectively 26.

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• LAB: single naive JUVENILES in 28.0 x 11.4 x 19.6 cm glass aquaria increased ventilatory frequency when exposed to the predator Pseudoplatystoma corruscans in an adjacent aquarium; no change in ventilatory frequency with a harmless fish Leporinus macrocephalus or an empty aquarium. Increasing ventilatory frequency improves oxygen uptake for upcoming flight 14.
• LAB: isolated predator-naive JUVENILES in 40 x 20 x 25 cm 12 L glass aquaria. On 10th day, paired with either smaller South American predator catfish spotted sorubim, Pseudoplatystoma corruscans, or smaller harmless South American threespot leporinus, Leporinus friderici. JUVENILES kept larger distance (measured as distance of fish eyes) to predator than non-predator. Higher number of dorsal fin displays and time of dorsal fin display compared to basal condition. Increase in time of fin display higher when paired with non-predator probably to enlarge body size and intimidate territory intruder. Three of seven JUVENILES displayed nipping of predator. Higher frequency of nipping (24.9%) and chasing (11.0%) of and lateral fights (1.9%) with non-predator. Results indicate innate predator recognition 78.

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• Individual differences in response to stress:
  • LAB: single male ADULTS in 60 x 28 x 31 cm 48 L glass aquaria were:
    a) confined by opaque partition to 10% aquarium volume. After 60 min, increased ventilatory frequency (ca 86 versus ca 70 opercular or buccal movements/min), but of nine ADULTS, five increased and four decreased their individual ventilatory frequency.
    b) AC shocked with 20 V, 15 mA and 100 Hz for 1 min each 4 min. After 60 min, ventilatory frequency within range of pre-stress level (ca 62-72 opercular or buccal movements/min). Of nine ADULTS, four increased and five decreased their individual ventilatory frequency 20.

^{In the structure of menu item 16 and the definition of "SHYNESS-BOLDNESS", we follow 100.}

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• Feeding resumption:
  • LAB: single JUVENILES placed in 40 x 24 x 20 cm glass aquaria for eight days differed in coping with novel environment and isolated state: the higher ventilatory frequency the later onset of feeding in novel environment (from ca 55 opercular beats/min and onset at day 1 to ca 180 opercular beats/min and onset at day 7). Tendency of higher food intake with higher ventilation rate and with later onset of feeding 27.
• Neophobia and boldness:
  • LAB: male JUVENILES with fast food intake recovery in a novel aquarium also showed less neophobia when exposed to a novel object, indicating boldness. No correlation between behaviour in novel environment, reaction to novel object, and number of body displacements in an emerged net. 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 26.

^{In the structure of menu item 16 and the definition of "EXPLORATION-AVOIDANCE", we follow 100.}

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• For aggressiveness and...
  ...establishing hierarchy ➝ D20,
  ...dominance ➝ D25,
  ...subordination ➝ D27,
  ...size-grading ➝ D28.

^{In the structure of menu item 16 and the definition of "AGGRESSIVENESS", we follow 100.}

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• LAB: male JUVENILES 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 (➝ D29) – a display of fearfulness? 26.

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• Chasing:
  • LAB: FINGERLINGS in 100 L tanks with 30% daily water exchange at densities 1, 2, 5, 10 IND/tank. On 61st day, chasing with net for 60 s increased plasma cortisol level compared to control groups indicating acute stress (ca 150-300 ng/mL versus 10-45 ng/mL). Higher cortisol level in 10 FINGERLINGS group compared to smaller groups (ca 300 ng/mL versus 150-175 ng/mL) 77.
  • LAB: cortisol levels of mixed-sex JUVENILES that were chased with a net for 60 s were higher than those of a control group for at least 2 h (ca 75 versus ca 15 ng/g body tissue). After 8 h, the levels were back to normal 95.
• Netting:
  • LAB: female ADULTS in 140 L tanks served as controls for tailclipped individuals (➝ D30) and were just netted and slightly applied pressure to the tailfin. Higher cortisol levels compared to untreated individuals until last observation time 24 h after handling (256.4 nM 6 h after handling, 111.5nM 24 h after handling versus 24.6 nM). Lower lactate levels compared to untreated individuals (0.7 versus 2.6 mM). Back to control levels at next observation time 24 h after handling 99.

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• LAB: confinement stress increased plasma cortisol levels in ADULTS held under white (590 lux; 18.1 versus 35.8 ng/mL) and green light (250 lux; 38.0 versus 47.2 ng/mL) but not under blue light (250 lux; 34.0 versus 27.6 ng/mL) 101.
• LAB: single ADULTS in 28 cm x 11.4 cm x 19.6 cm aquaria were confined by opaque partition to 10% of water volume:
  a) After 30 min confinement, higher ventilatory frequency until second measurement at 5 min after stress compared to non-confined ADULTS (ca 110 versus 100 beats/min); back to normal at third measurement 15 min after stress. Higher cortisol level until 35 min after stress (100-150 ng/mL versus 40-60 ng/mL), back to normal at next measurement 75 min after stress.
  b) Second experiment with different periods of confinement: highest difference to basal ventilatory frequency directly after stress in ADULTS confined for 30 min and ADULTS from control group where partition was dipped in water without actually confining. Faster decrease in control group than 30 min confinement group, but no return to basal frequencies in either group at end of measurement period at 27 min. Lower difference to basal ventilatory frequency directly after stress in ADULTS confined for 30 s, 5 min, and 15 min. Return to basal frequencies at around 15-18 min in 30 s- and 5 min-groups, around 27 min in 15 min-group 28.
• LAB: single individuals in 12 x 20 x 30 cm aquaria under 12 hours white, blue, or yellow light (ca 50 lux each) per day (06:00-18:00 h) for seven days. 15 min confinement on the morning of day 8 increased ventilatory frequency by average 8 opercular or buccal movements/min until 4 minutes after stress, more under white compared to blue light; yellow light in between. Back to basal level from 6 min after stress on 29.

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• Stunning rules: to minimise pain reactions and enhance welfare before slaughter:
  1. induce insensibility as fast as possible,
  2. prevent recovery from stunning,
  3. monitor effectiveness (observations, neurophysiological measurements) 102.

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• Time to loss of vital signs (no response to needle scratches):
  a) electrical stunning with 50 Hz for 180 s: LAB, ADULTS: 30 s 82,
  b) 50:50 ice water mixture: LAB, ADULTS: 20 min 82,
  c) CO2 narcosis: LAB, ADULTS: 30 min 82.
• Electrical stunning:
  • LAB: for specifics on electrical current (depending on water conductivity) ➝ 81:
    Experiment 1: ADULTS in 50 x 20 x 70 cm plexiglass box restrained with clamp in lower jaw and plastic tie-ribs around body. Top-to-bottom stunning of 50 Hz for 1 s in fresh water. 9 s tonic phase with tense muscles, 13 s clonic phase with uncontrollably contracting muscles, 11 s exhaustion with flaccid muscles. Two of 28 ADULTS did not display epileptiform insult probably due to heart failure. In 16 of 28 ADULTS, response to needle scratches 30 s after stunning.
    Experiment 2: see Experiment 1 but 5 s stun. No response to needle scratches in 24 of 24 ADULTS until 49 s after stunning when ADULTS where placed in iced water. Another eight ADULTS showed isoelectric line at 56 s after stunning and did not recover.
    Experiment 3: see Experiment 1 but applied head to tail. 9 s tonic phase with tense muscles, 13 s clonic phase with uncontrollably contracting muscles, 11 s exhaustion with flaccid muscles. In eight of eight ADULTS, response to needle scratches after the exhaustion phase.
    Experiment 4: side-to-side stunning of 133 Hz pulsed square wave alternating current for 1 s in seawater. 28 s tonic/clonic phase, 18 s exhaustion with flaccid muscles. In six of 17 ADULTS, response to needle scratches 30 s after stunning.
    Experiment 5: see Experiment 4. After 1 s stun in five ADULTS, 38-52 s muscle contractions, 68-95 s uprighting. After 5 s stun in another five ADULTS, 181-489 s muscle contractions, 438-1139 s uprighting.
    Experiment 6: see Experiment 4 but 5 s stun, thereafter gill cut. Of ADULTS gill-cut on the table, one responded to needle scratches 1 and 5 min later. In two of four ADULTS gill-cut under water, response to needle scratches 10 min after stunning.
    Experiment 1-6: no broken bones, bruises, blood spots 81.

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• LAB: immediately after death, higher cortisol levels in ADULTS stunned in 50:50 ice water mixture (22.2 ng/mL versus 15.9-17.5 ng/mL) compared to electrical stunning or CO2 narcosis. Could be due to higher dissolved oxygen in ice water (19.9 mg/L versus 6.2-6.3 mg/L) than in the other conditions. Levels below 50 ng/mL are considered low stress 82.

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