Reviewer: Kerstin Glaus
Editor: Billo Heinzpeter Studer

• Initial release: 2016-09-15
• Appearance version: 2022-06-12
• Major version: 2018-07-08
• Minor version: 2020-01-18

Cite as: »Volstorf, Jenny, and João L. Saraiva. 2020. Perca fluviatilis (Dossier). In: fair-fish database, ed. fair-fish. World Wide Web electronic publication. Version B | 1.1. https://fair-fish-database.net.«

• For feeding → 1.
• For daily rhythm → 2 3.
• For schooling, shoaling → 2 4.

• For courtship and spawning → 5.
• For dominance, subordination, and aggression → 6.
• For learning → 7 8.

• Observations inland waters continental Europe: lake of Robertville, Belgium 10, lake Varese, north-west Italy 11, lake Wallersee, Austria 12, Orlik reservoir, Czech Republic 4, Rimov reservoir, Czech Republic 13 14, river Meuse, Belgium 15, Slapy reservoir, Czech Republic 4.
• Observations inland waters England: loch Kinord and loch Davan, Scotland 5, lake Windermere, north-west England 3.
• Observations inland waters Scandinavia: lake Abborrtjärn 3, Sweden 16, lake Ängersjön, Sweden 17 18 19, lake Bjännsjön, Sweden 17 18, lake Fisksjön, Sweden 17 18 19, lake Harkkojärvi 1 20, lakes Kinnasjärvi and Koppelojärvi 20, lake Nimetön, Finland 1, lake Stöcksjön, Sweden 17 18, lake Trehörningen, Sweden 17 18, lake Tuopanjärvi, Finland 20, lake Ulvenvannet, Norway 18.
• Observations coastal waters: off Norrbyn, Gulf of Bothnia, Sweden 18.

• Observations continental Europe: lake Chabarovice, Czech Republic 13.
• Observations Oceania: lake Pounui, New Zealand 2.

• Observations Bass WILD: Micropterus salmoides: lake Varese, north-west Italy 11.
• Observations Brown trout WILD: Salmo trutta: lake Pounui, New Zealand (introduced) 2.
• Observations Bullhead catfish WILD: Ictalurus melas: lake Varese, north-west Italy 11.
• Observations Carp WILD: Cyprinus carpio, Carassius carassius: lake Varese, north-west Italy 11.
• Observations Eel WILD: Anguilla australis Richardson and A. dieffenbachii Gray: lake Pounui, New Zealand (introduced) 2, Anguilla anguilla: lake Varese, north-west Italy 11.
• Observations Peled WILD: Coregonus peled: forest lakes Horkkajärvi and Nimetön, southern Finland 1.
• Observations Tench WILD: Tinca tinca: lake Varese, north-west Italy 11.

• Plants:
  • WILD: JUVENILES-ADULTS were observed with floating Sphagnum peat moss: forest lake Nimetön, southern Finland 1.
  • WILD: JUVENILES-ADULTS were observed with Carex rostrata, Menyanthes trifoliata, Lobelia dortmanna, Nymphaea alba: lake Abborrtjärn 3, Sweden 16.
  • For substrate and spawning → D1.
• Rocks and stones:
  • WILD: JUVENILES-ADULTS were found over rocky bays of rocks and rubble: Rimov reservoir, Czech Republic 13.
• Sand and mud:
  • WILD: JUVENILES-ADULTS were found over sandy and muddy beaches: Rimov reservoir, Czech Republic 13.
• Other substrate: no data found yet.

• Plants: no data found yet.
• Rocks and stones: no data found yet.
• Sand and mud: no data found yet.
• Other cover: no data found yet.
• For shelter and establishing hierarchy → D2.

• Environmental enrichment and aggression:
  • LAB: in groups of three 0+ JUVENILES in 10 L aquaria with grey plastic tube (3 cm diameter, 8 cm length, open on one side) at bottom, dominant and rival JUVENILES mainly attacked and chased each other. Less often: bites, displays. No aggression in control aquaria without tube, no aggression during feeding 6.

• Observations: 4.4±0.0 se 21.

• Carnivorous D3. 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 22 or even 1/3 23 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 24, the individual fish gets overlooked and, thus, suffering increases at rearing, live marketing, and slaughtering levels 25.

• Food items: carnivorous:
  • WILD, JUVENILES-ADULTS: mainly Zooplankton, crustacean Zooplankton (Asellus aquaticus), insect larvae (Ephemeroptera, Trichoptera, Chironomidae, Odonata), insects (Heteroptera): forest lakes Horkkajärvi and Nimetön, southern Finland 1.
  • WILD, JUVENILES-ADULTS: widely-varied diet, depending on season: mainly insect larvae or pupae (Chaoboridae, Chironomidae) with peak in April, crustacean Zooplankton (Cladocera, Daphnia sp., Leptodora kindtii, copepods) with peak in April, fish (Scardinius erythrophthalmus, Rutilus rutilus) and crayfish Orconectes limosus with peaks in July and September: lake Varese, north-west Italy 11.
  • For cannibalism → D4.
• Food items and habitat: no data found yet.
• Food items and life stages: mainly Zooplankton as JUVENILES, increasing proportion of fish with increasing age:
  • WILD: lake Abborrtjärn 3, Sweden 16:
    0+ JUVENILES: mainly Zooplankton, chironomids, macroinvertebrates,
    1+ JUVENILES: mainly macroinvertebrates, zooplankton and chironomids.
  • WILD: forest lake Horkkajärvi, southern Finland 1:
    JUVENILES of 7-9.9 cm: mainly Zooplankton,
    JUVENILES of 10-12.9 cm: mainly Zooplankton, crustacean Zooplankton (Asellus aquaticus), and insect larvae (Trichoptera, Chironomidae),
    ADULTS of 13-15.9 cm: mainly crustacean Zooplankton (Asellus aquaticus), insects (Heteroptera), and insect larvae (Odonata, Trichoptera).
  • WILD: forest lake Nimetön, southern Finland 1:
    JUVENILES of 7-9.9 cm: mainly Zooplankton,
    JUVENILES of 10-12.9 cm: mainly insect larvae (Ephemeroptera, Odonata, Chironomidae),
    ADULTS of 13-15.9 cm: mainly Zooplankton, insect larvae (Ephemeroptera, Chironomidae), and crustacean Zooplankton (Asellus aquaticus),
    ADULTS of 16->19 cm: mainly insects (Heteroptera) and insect larvae (Odonata).
  • WILD: three diet shifts in lake Varese, north-west Italy 11:
    JUVENILES of 9-12.5 cm: mainly crustacean Zooplankton (65%) and insect larvae/pupae (35%),
    ADULTS of 12.5-16 cm: mainly insect larvae/pupae and crayfish (63%) and crustacean Zooplankton (37%),
    ADULTS of 16-18 cm: mainly insect larvae/pupae (65%), fish (22%), crustacean Zooplankton (13%),
    ADULTS >18 cm: mainly fish (55%).
  • FARM: in natural ponds 28:
    Until 20 days post hatch: Zooplankton Daphnia, rotifers (Keratella, Asplancha), copepods, nauplius larvae,
    25-40 days post hatch: slight size bimodality with a) larger (3-7 cm difference) FRY preying on Abramis brama larvae and smaller FRY, macroinvertebrates (ephemeropterans, odonates, chironomids), b) smaller FRY sticking mainly to Zooplankton,
    >40 days post hatch: a) larger 0+ JUVENILES: mainly fish (P. fluviatilis, Abramis brama), macroinvertebrates, b) smaller 0+ JUVENILES: mainly macroinvertebrates, Zooplankton.
• Food preference: no data found yet.
• Food partitioning: no data found yet.
• Prey density: no data found yet.
• Prey size selectivity: no data found yet.
• Particle size: no data found yet.

• WILD: JUVENILES-ADULTS searched for food in littoral zone, snipping for food items one by one: forest lakes Horkkajärvi and Nimetön, southern Finland 1.
• For foraging and vision → D5.

• For feeding and low temperatures and disturbance → D6.

• Daily rhythm:
  • WILD: during night, little activity, single JUVENILES-ADULTS rested on bottom in open water: lake Pounui, New Zealand (introduced) 2.
  • WILD, ADULTS: major activity peak at dusk ca 18:00 h and smaller peak at dawn ca 06:00 h in October-April with high surface visual irradiance and clear water during the day. Several peaks throughout photophase in May-September with lower light intensities during the day due to reduced surface visual irradiance and algal bloom. Observations indicate that ADULTS avoid high light intensities: lake Windermere, north-west England 3.
• Nocturnal activity: → Daily rhythm.
• Phototaxis: no data found yet.

• LAB: at density of 5.1 kg/m³, JUVENILES in 80 x 30 x 35 cm aquaria taped with black foil on all sides and subjected to artificial illumination: 7,000 lux during 14 h daytime including 3 h dusk or dawn transition, 10 h nighttime with either 1, 10, or 100 lux (control: 0 lux at nighttime). After 10 days, reduced mean melatonin concentration in tank water under 10 and 100 lux compared to control (ca 0.8-1.5 pg/L/kg versus ca 6-9 pg/L/kg); 1 lux in between (ca 1.8-2.5 pg/L/kg). Circadian rhythm of melatonin production with increase after dusk and decrease after dawn under 1 lux but not under 10 or 100 lux. Lower median cortisol concentration in tank water under 100 lux compared to 1, 10 lux, and control (ca 3-4.5 ng/L/kg versus ca 4-6 ng/L/kg). Results indicate that light influences circadian melatonin rhythm, but nocturnal lighting does not influence stress 29.

• Standard temperature range: 6.1-28 °C:
  • Observations WILD, FRY: average 12.1-20.4 °C: Rimov reservoir, Czech Republic 14.
  • Observations WILD, JUVENILES-ADULTS: 6.1-19.5 °C: lake Windermere, north-west England 3, surface temperature 6.7-24.2 °C: lake Pounui, New Zealand (introduced) 2, 22-28 °C in epilimnetic layer, 9-11 °C in hypolimnetic layer: lake Varese, north-west Italy 11.
• Temperature preference: no data found yet.
• For temperature and...
  ...depth → D8,
  ...spawning → D1.

• Temperature must exceed: 13-14 °C:
  • WILD, JUVENILES: growth started with water temperatures 13-14 °C: lake Windermere, north-west England 30.
• Temperature must not go beyond: no data found yet.
• Optimal temperature for growth: no data found yet.
• For temperature and feeding → D6.

• Observations WILD, FRY: ca 6-7 mg/L at 7-9 m, ca 8-9 mg/L at 0-2 m: Rimov reservoir, Czech Republic 14.
• Observations WILD, JUVENILES-ADULTS: 100-150% in epilimnetic layer, <10% in hypolimnetic layer: lake Varese, north-west Italy 11.

• Salinity tolerance:
  • Natural and introduced distribution in fresh water or brackish water at most D9 D10.
• Standard salinity range: no data found yet.

• Standard turbidity range: no data found yet.
• Secchi depth (water transparency): 1.1-7.5 m:
  • Observations WILD, LARVAE-JUVENILES: 1.1-3.8 m: Orlik reservoir, Czech Republic, 6-7.5 m: Slapy reservoir, Czech Republic 4.
  • Observations WILD, JUVENILES-ADULTS: 3 m: lake Varese, north-west Italy 11.
  • Observations WILD, ADULTS: 2.3 m: Rimov reservoir, Czech Republic, 6.8 m: lake Chabrovice, Czech Republic (introduced) 13.
• For Secchi depth and spawning → D1.

• Observations: 31.

• Depth range in the wild: 0-18.5 m:
  • Observations WILD, LARVAE: 0-2 m: lake Abborrtjärn 3, Sweden 16.
  • Observations WILD, FRY: maximum 1 m (littoral), 0-2 m (epipelagic), 7-9 m (bathypelagic): Rimov Reservoir, Czech Republic 14.
  • Observations WILD, LARVAE-JUVENILES: 4.5-18.5 m: Orik reservoir, Czech Republic 4.
  • Observations WILD, JUVENILES-ADULTS: schools observed in 0.5-2 m depth: lake Pounui, New Zealand (introduced) 2, 2-6 m: lake Abborrtjärn 3, Sweden 16.
  • Observations WILD, ADULTS: 1-12 m: lake Windermere, north-west England 3, 1.5 m: channel in Norden, Germany 8.
  • For depth and spawning → D1.
• Depth in cages or tanks: no data found yet.
• Depth preference: no data found yet.
• Depth and daily rhythm:
  • WILD: during summer, ADULTS moved deeper to 1.5-3 m in early evening to feed on JUVENILES: lake Pounui, New Zealand (introduced) 2.
• Depth and low temperatures:
  • WILD: annual catch peak in 1-12 m in August at 19.5 °C, lowest catch in January at 6.1 °C. Majority of catch in 1-6 m depth during July-August, majority of catch in 4-12 m rest of the year: lake Windermere, north-west England 3.
  • WILD: JUVENILES-ADULTS moved deeper (seldomly >6 m) in autumn at surface temperature ca 16 °C: lake Pounui, New Zealand (introduced) 2.
• 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.

• Observations time from fertilisation until hatching: no data found yet.
• Observations size WILD: 0.9-1.4 mm diameter: lake Pounui, New Zealand (introduced) 2, 0.9-1.6 mm: Lochs Davan and Kinord, Scotland 5.
• Observations weight WILD: average 8.7 mg: lake of Robertville, Belgium 10.

• Observations age at yolk sac absorption and mouth opening LAB: days 15-17 32.
• Observations TOTAL LENGTH WILD: 5.2-6.5 mm fork length after hatching: lake Pounui, New Zealand (introduced) 2.
• Observations TOTAL LENGTH and weight LAB: 4.8-5.3 mm after hatching 32, mean 0.9 mg after hatching 10, mean 6.5 mm, 1 mg after hatching 33.

• Observations age at beginning of exogenous feeding LAB: day 4-19 35↶32.
• Observations age and TOTAL LENGTH WILD: 16-34 days, range 9-23 mm, average 13.7-19.3 mm: Rimov reservoir, Czech Republic 14.
• Observations age and weight LAB: 10 days, 18-22 mg 15.

• Observations age: → D11.
• Observations TOTAL LENGTH WILD: 9-12.5 cm: lake Varese, north-west Italy 11.
• Observations weight FARM: 57.8 g 36.
• Observations age and weight LAB: average 39.6 g 37, average 59.6 g 38, 63.5-78.6 g 39, day 77, ca 5-6 g: early gametogenesis in males and females 15.
• Sexual maturity: males: 0-2 years, 10.2-13.7 cm or less, 9-18 g, females: 1-4 years, 10-19.9 cm, 23-126 g:
  • Observations age, TOTAL LENGTH, and weight of males WILD: 2 years, 10.2-13.7 cm, 9-18 g: lake Windermere, north-west England 30, during first year: lake Pounui, New Zealand (introduced) 2, mainly 2 years and 6 cm fork length: Loch Kinord and Loch Davan, Scotland 5, 2 years and 8-10 cm: forest lake Horkkajärvi, southern Finland 1, from age 0+ on, 73% at age 1+: lake Varese, north-west Italy 11.
  • Observations age, TOTAL LENGTH, and weight of females WILD: 3-4 years, 13.4-19.9 cm, 23-126 g: lake Windermere, north-west England 30, during second year: lake Pounui, New Zealand (introduced) 2, mainly 4 years and 15 cm fork length: Loch Kinord, Scotland, from 3 years and 17-18 cm fork length on: Loch Davan, Scotland 5, 3 years and 10-11 cm: forest lake Horkkajärvi, southern Finland 1, 12-13 cm: forest lake Nimetön, southern Finland 1, from age 1+ on, 76% at age 2+: lake Varese, north-west Italy 11.

• Observations age, TOTAL LENGTH, and weigth WILD: females: 12-15 years, 20.4-25.1 cm, 115-166 g, males: 10 years, 15.8-22.7 cm, 105-132 g: lake Windermere, north-west England 30, females 19.7-34.3 cm (mean 25.9 cm), males 15.1-27.3 cm (mean 23.8 cm): lake Windermere, north-west England 3, male: 6 years and 26.2 cm fork length, 8 years and 21.7 cm fork length, female: 10 years and 42.4 cm fork length, 12 years and 30.9 cm fork length: lake Pounui, New Zealand (introduced) 2, 89.7-129.7 g at age 4, 367.3-880.0 g at age 6-15: Loch Kinord and Loch Davan, Scotland 5, 22 g at 6 years, 13-16 cm at age 8+ (stunted): forest lake Horkkajärvi, southern Finland 1, 62 g at 6 years: forest lake Nimetön, southern Finland 1, 10-12 cm: channel in Norden, Germany 8, ca 27 cm at age 7+ years: lake Varese, north-west Italy 11.
• Observations TOTAL LENGTH FARM: 19-33 cm 28.

• Growth:
  • WILD: growth halted during band formation on opercular bones in winter and early spring: lake Pounui, New Zealand (introduced) 2.
• Natural growth rate:
  • WILD, JUVENILES: estimated growth rates of ca 5 cm in fourth and fifth year coincided with cannibalism: lake Äbborrtjärn 3, Sweden 16.
  • WILD, JUVENILES-ADULTS: growth rates estimated at ca 7 cm in first year, 4-5 cm in second year, 1-3 cm in third and fourth year, thereafter ca 1-2 cm/year: lake Windermere, north-west England 30.
  • WILD, JUVENILES-ADULTS: growth rates estimated at ca 5 cm in first year, 3-4 cm in second year, 2-3 cm in third and fourth year, thereafter ca 1-2 cm/year: forest lakes Horkkajärvi and Nimetön, southern Finland 1, lake Abbörrtjärn 3, Sweden 16.

• Observations bimodal pattern WILD, JUVENILES-ADULTS: range of females 10.5-29.4 cm (mean 20 cm), males 10-27.5 cm (mean 17.7 cm), mean total body mass for females 112 g, males 71 g: lake Varese, north-west Italy 11.
• Beginning of noticeable size difference:
  • WILD, JUVENILES: females grew faster than males after the first year: lake Pounui, New Zealand (introduced) 2.
  • WILD, JUVENILES-ADULTS: similar growth of males and females in first two years, then mature individuals larger than immature individuals, mature females grew faster than mature males: lake Windermere, north-west England 30.
  • WILD, JUVENILES-ADULTS: faster growth of males in first two years, from then on faster growth of females: forest lakes Horkkajärvi and Nimetön, southern Finland 1.

• Nest building and substrate: no data found yet.
• Nest building and water velocity: no data found yet.
• Nest building and water depth: no data found yet.
• Nest building: no data found yet.
• For breeding type → D13.

• Courtship sequence:
  • LAB, ADULTS: in aquarium, female with gravid belly attracted 4-5 males. One male followed while she circled water plants, frequently changed directions, often spiralled upward and paused in between. Male stayed behind at 1-2 body lengths, sometimes prodding the female's vent. Remaining males in attendance stared at vent, followed if female changed site and replaced male if broke off. No aggression recorded. Female circled for 30 min, increasing in speed 5.
• Courtship duration: 30 min → Courtship sequence.

• Polyandry:
  • Observations LAB, ADULTS: 5.

• Spawning substrate: gravel, macrophytes, tree roots, branches:
  • Observations WILD, ADULTS: macrophytes in 2-3 m depth: lake Pounui, New Zealand (introduced) 2, wide variety including gravel, aquatic macrophytes, tree roots, dead branches, and artificial substrate composed of intermeshed hornbeam Carpinus betulus and hazel Corylus avellana branches positioned at bottom in 2-8 m depth: lake Varese, north-west Italy 11.
  • WILD, ADULTS: more egg strands found in grassy than rocky bays or main reservoir (ca 3-5 strands/100 m versus 0.1-0.5 strands/100 m), mostly on reed canarygrass but also goat willow Salix caprea, logged trees, branches, raspberry Rubus ideaus, blackberry Rubus fruticosus, dog rose Rosa canina, common rush Juncus effusus: Rimov reservoir, Czech Republic 13.
• Spawning season: winter-spring:
  • Observations WILD, ADULTS: winter, early spring: lake Pounui, New Zealand (introduced) 2, April: river Sunoga 32, pre-spawning females at late-developing and gravid stage were caught in April and May at 11-22 °C, eggs were caught in April and May: lake Varese, north-west Italy 11, mid April-beginning of May, 14-16 °C: Rimov reservoir, Czech Republic 13.
• Spawning (day)time: no data found yet.
• Spawning temperature: → Spawning season.
• Spawning salinity: no data found yet.
• Spawning and water velocity: no data found yet.
• Spawning depth: 0-12 m depending on waves, submerged vegetation, and Secchi depth:
  • WILD, ADULTS: Rimov reservoir (Czech Republic) little vulnerable to wind and thus waves through surrounding forests and meanders, flooded vegetation in littoral zone, Secchi depth 2.3 m: 98.1% of 156 egg strands in <0.5 m, in grassy bays mostly 0-0.1 m. Deeper deposition (0.5-1 m) in observation year with low water level and missing submerged vegetation. Lake Chabrovice (Czech Republic) exposed to higher wind velocities because no surrounding forest, abundant submerged vegetation partly to deepest depth, Secchi depth 6.8 m: 90.5% of egg strands in >3 m, 95% in <12 m, none in <1 m 13.
• Spawning density: no data found yet.

• Male:female ratio resulting in spawning:
  • Observations WILD, ADULTS: 1:4.6: lake Pounui, New Zealand (introduced) 2.
• Composition of broodstock: no data found yet.

• Spawning sequence:
  • WILD, ADULTS: males left spawning grounds immediately after spawning: lake Pounui, New Zealand (introduced) 2.
  • LAB, ADULTS: in aquarium, female rapidly spiralled clockwise through water plants for 5 s while releasing single egg strand. At least two of 4-5 males in attendance simultaneously released milt 5.
• Spawning duration: → Spawning sequence.

• Number of spawns: no data found yet.
• Fecundity per spawn:
  • Observations absolute fecundity WILD, ADULTS: 2,657-63,858 eggs at 14.6-42.2 cm fork length: lake Pounui, New Zealand (introduced) 2, 9,277-18,872 at age 4, 34,168-74,124 at age 6-15: Loch Kinord and Loch Davan, Scotland 5, mean 5,038 at age 2+ and 17.5-19.5 cm, mean 10,913 at age 3+ and 20-22 cm, mean 18,551 at age 4+ and 23-25 cm: lake Varese, north-west Italy 11.
  • Observations relative fecundity WILD, ADULTS: 141,000 eggs/kg at 14.6 cm fork length, 33,000 eggs/kg at 42.2 cm fork length: lake Pounui, New Zealand (introduced) 2, 50-146 eggs/g at age 4-15: Loch Kinord and Loch Davan, Scotland 5, mean 105,271 at age 2+, mean 132,622 ate age 3+, mean 131,252 at age 4+: lake Varese, north-west Italy 11.

• Observations: → D1.

• LAB, ADULTS: projecting a stimulus onto the right or left side of a screen in front of the tank, ADULTS responded by putting their head into one of two response chambers and received reward if correct. After two consecutive correct responses, stimulus intensity decreased; after incorrect response, stimulus intensity increased. ADULTS were sensitive to wavelengths 400-750 with peaks at 530-560 nm (green) and 660-680 nm (red) and a smaller peak at 400 nm (violet) 40.

• Vision and predator avoidance:
  • LAB: three naive 0+ JUVENILES from wild-caught eggs in 30 x 30 x 20 cm 10 L aquaria with predator pike Esox lucius in transparent bag. During 15 min, decrease in food intake compared to control group (350-450 µg/IND/15 min each of large and small prey Daphnia magna versus 500-600 µg/IND/15 min). Sharper decrease (150-200 µg/IND/15 min each of large and small prey Daphnia magna versus 500 µg/IND/15 min) when additionally 150-200 mL water from aquarium with food-deprived pike dripped in indicating synergistic effect of visual and olfactory cues 12.

• LAB: LARVAE from wild-caught eggs in either black or grey 100 L flow-through tanks at 100-150 lux light intensity fed Artemia nauplii. After five weeks, higher weight (51.1 mg versus 23.8 mg) and higher length (19.1 mm versus 15.7 mm) in black than grey tanks. No difference in mortality (ca 75%). Results indicate visual foraging and better visibility via contrast of light nauplii in dark tanks 33.
• LAB: JUVENILES in 0.1 m³ tanks lined with either black, grey, or white PVC sheets and light intensity of 1,117 or 222 lux fed dark food pellets. After three weeks, no effect of tank colour under 1,117 lux intensity; under 222 lux, higher feed intake (ca 1.0% versus 0.7% group average weight/IND/d) and higher specific growth rate (ca 0.7 versus 0.3) in white compared to black tanks, grey tanks in between. No difference in energy expenditure between light intensities indicates no stress. Results indicate visual foraging and better visibility via contrast of dark feed in lighter tanks 38.

• Olfaction and predator avoidance:
  • LAB: three naive 0+ JUVENILES from wild-caught eggs in 30 x 30 x 20 cm 10 L aquaria. During 15 min, 150-200 mL water from aquarium with food-deprived pike Esox lucius dripped in. No effect on food intake in JUVENILES. Decrease in food intake compared to control group (150-200 µg/IND/15 min each of large and small prey Daphnia magna versus 500 µg/IND/15 min) only when pike was additionally in the aquarium in a transparent bag. Results indicate that visual cues may be more important than olfactory cues in predator avoidance, maybe because in turbulent waters predator scent is dispersed in all directions and not reliable 12.

• Hearing type:
  • LAB, JUVENILES-ADULTS: hearing GENERALIST 41 42.
• Hearing spectrum:
  • LAB: JUVENILES-ADULTS in a plastic tub with diameter 33 cm and 13 cm depth lined with acoustically absorbent material. Audiogram under control laboratory conditions and playing back noise from still (40-60 dB), slow flowing (60-80 dB), and fast flowing rivers (80-100 dB). Greatest hearing sensitivity at 0.1-0.3 kHz with hearing threshold at 81.7-87.7 dB re 1 µPa. Combination with noise from different habitats did not influence hearing sensitivity but increased hearing threshold by 0-7.2 dB at two still waters and 5.2-12.5 dB at fast flowing river, slow flowing in between 41.
  • LAB: ADULTS in an aluminium tube ending with rubber membranes connected to piston and vibrator were exposed to particle movement by moving the pistons. ADULTS reacted to infrasound from 30 to 0.3 Hz (→ D14). Blocking the lateral line system by exposing ADULTS to water containing Co²⁺ did not affect the hearing thresholds. Hearing infrasound probably involves the inner ear, not the lateral line system 7.

• LAB: JUVENILES in 3 L bucket were exposed to boat noise (recorded in Danube river and lakes Mondsee and Traunsee, 153 dB), Gaussian noise (by noise generator, 156 dB), and no noise for 30 min. 99% increase in water cortisol under boat noise compared to no noise (ca 0.3 versus 0.2 ng/L water/g body weight), no increase under Gaussian noise. Results indicate higher influence of more fluctuating (in amplitude and frequency) compared to continuous sound 42.

• WILD: ADULTS in Finnish lakes Harkkojärvi, Kinnasjärvi, Koppelojärvi, and Tuopanjärvi. In moderately humic lake Tuopanjärvi, more lateral and dorsal yellowness, more colourful and lighter tails, and more colourful and darker bellies in littoral than pelagic ADULTS. In humic lakes Kinnasjärvi and Koppelojärvi, more yellow and more red lateral and dorsal skin in littoral than pelagic ADULTS. In most humic lake Harkkojärvi, more red lateral and dorsal skin in littoral than pelagic ADULTS. Males with redder, yellower, and darker bellies than females only in most transparent lake. Results indicate colouration is adjusted to habitat – colour for intra-specific communication in littoral, dullness for predator avoidance in pelagic – and that difference is most pronounced in most transparent lake 20.

• Observations shoal WILD, LARVAE-JUVENILES: in May, 3-6 m thick layer of bathypelagic LARVAE-JUVENILES of average 10.4 mm TOTAL LENGTH along 29 km of Slapy reservoir, Czech Republic, in 6.5-12.5 m depth. No shoaling. In June, 1-7 m thick layer of bathypelagic LARVAE-JUVENILES of average 31.8 mm TOTAL LENGTH along 52 km of Orik reservoir, Czech Republic, in 4.5-18.5 m depth 4.
• Observations school WILD, JUVENILES-ADULTS: up to 40 of similar size and both sexes schooled during the day: lake Pounui, New Zealand (introduced) 2.

• Observations WILD: layer of bathypelagic LARVAE-JUVENILES with 11,699-61,123 IND/ha or 0.4-2.6 IND/m: Slapy reservoir, Czech Republic, 2,197-89,111 IND/ha or 0.1-8.1 IND/m: Orlik reservoir, Czech Republic 4.
• Observations WILD, FRY: 90 IND/100 m in 0-2 m and average 20.4 °C, 26 IND/100 m in 7-9 m and average 12.9 °C: Rimov reservoir, Czech Republic 14.
• Observations WILD, JUVENILES: estimated at 50-150 IND/ha of age 0+, 300-3,500 IND/ha of age 1+, 30-1,000 IND/ha of age 2+: lake Abborrtjärn 3, Sweden 16.
• WILD: stunted growth in forest lake Horkkajärvi with density 1,750 IND/ha of JUVENILES-ADULTS >8.5 cm compared to forest lake Nimetön (both in southern Finland) with 530 IND/ha 1. Authors suggested higher food competition due to higher density in Horkkajärvi as one of reasons for stunting.

• For stocking density and...
  ...cannibalism → D4,
  ...aggression → D15.

• Hierarchy and group size: in small groups, JUVENILES establish linear dominance hierarchies:
  • LAB: in groups of three 0+ JUVENILES in 10 L aquaria with grey plastic tube (3 cm diameter, 8 cm length, open on one side) at bottom, one became dominant; in eight of 10 aquaria, one to two became subordinate; in four of 10 aquaria, one to two became rival, meaning JUVENILES did not avoid aggressive encounters with dominant and entered dominant's territory 6.
• Establishing hierarchy:
  • LAB: groups of three 0+ JUVENILES in 10 L aquaria with grey plastic tube (3 cm diameter, 8 cm length, open on one side) at bottom. Whereas JUVENILES usually entered tube together after 5-30 min, left after 1-2 h as dominant, subordinate, or rival (→ Hierarchy and group size). Social position might still change after 6-8 h. From 10 h on, fixed 6.

• Features of dominance:
  • LAB: dominant JUVENILES defended shelter, had higher feeding intake than subordinate (15.0-17.1 Daphnia magna/IND/min versus 4.1-4.1 Daphnia magna/IND/min) 6.

• Features of subordination:
  • LAB: subordinate JUVENILES avoided encounters, stayed in corner of aquarium or at surface 6.
• Hierarchy and stress: no data found yet.

• WILD: contribution of 0+ JUVENILES to diet: in 1+ JUVENILES: 0-10%, in 3-5+ JUVENILES: 0% in some years to 100% in others. Most likely not due to decreased Zooplankton density but to (inshore) habitat overlap – and thus food competition – and increased energy demand: lake Abborrtjärn 3, Sweden 16.
• WILD: given proportion of JUVENILES with gape larger than average body depth, cannibalism risk in five Swedish lakes ranged from 0.2% in lake Fisksjön to 73.6% in lake Ängersjön 17.
• WILD: estimated daily cannibalistic attack rate: >20% for 1-6 cm JUVENILES with peak of 100% for 2.5 cm JUVENILES in lake Fisksjön, Sweden, >10% for 1.5-8 cm JUVENILES with peak of 30% for 3.5 cm JUVENILES in lake Ängersjön, Sweden 19.
• WILD, JUVENILES-ADULTS: little cannibalism, only two cases observed: forest lakes Horkkajärvi and Nimetön, southern Finland 1.
• FARM: 0+ JUVENILES stocked in natural ponds of 0.4-0.7 ha as eggs. At 25-40 days post hatch, depletion of Zooplankton. At 125 days post hatch, larger size bimodality in 0+ JUVENILES stocked with bream Abramis brama (up to 11 cm difference versus ca 4 cm) than 0+ JUVENILES without bream. Result indicates that after depletion of main food source, large 0+ JUVENILES turned to feeding on bream larvae and gained more energy which increased bimodality and enabled cannibalism 28.
• LAB: eggs from same wild-caught strand in 100 L floating cages at stocking densities 1,000, 3,163, 10,000 eggs/cage. Partial cannibalism where the heads remained started at day 10 post hatching, complete cannibalism between days 14 and 18. After 22 days, bimodal weight distribution with FRY <11.2 mg deemed "prey", FRY >mean 51.2 mg deemed "cannibals". In prey, tendency of higher weight in high stocking density than low density (11.2 mg versus 7.3 mg), medium density in between (9.7 mg); in cannibals, tendency of higher weight in high and medium compared to low density (68.1-74.5 mg versus 51.2 mg). Tendency of higher survival in high density compared to low density (20.1% versus 14.8%), medium in between (18.9%), due mainly to tendency of lower cannibalism in medium and high compared to low density (28-34.4% versus 53.2%). Higher proportion of cannibals in final population in low than medium and high density (20.9% versus 4.2-9%). No difference in partial cannibalism with remaining heads (1.4-1.5%). Tendency of higher natural mortality in high and medium compared to low density (44.1-51.7% versus 30.7%) 10.
• LAB: 10 day old LARVAE in 30 L tanks at 50 IND/L originating from one of two females and either an XY or XX male in groups of mixed-sex full siblings, all-female full siblings, mixed-sex half-siblings, or all-female half-siblings. After 77 days, no difference in growth (5.1-6.1 g). Higher survival in mixed-sex and all-female full siblings from one female than the other (59-61% versus 36-41%). Peaks of incomplete cannibalism, where the heads remain, in weeks 1-2 and 5-6. Higher frequency of incomplete cannibalism in mixed-sex or all-female full siblings from one female than the other (27.2-45.1% versus 6.6-20.2%). Results indicate genetic component in survival and cannibalism but authors refer to small sample size of four broodstock ADULTS 15.

• FARM, JUVENILES: densities of 25-30 kg/m³ decreased aggression personal communication Thomas Janssens 2017.

• LAB: in a group of 5, ADULTS learned to associate a conditioned stimulus (a sound) – in place of the unconditioned stimulus of a mild electric shock to the tail – with a conditioned response (stress = decrease in heart rate). Allowed determination of hearing spectrum (→ D18) 7.

• Managing self-feeder:
  • LAB: ADULTS learned how to manage a self-feeder by pulling a piece of lead attached to a string of wool (→ D6) 8.
• For operant conditioning and visible spectrum → D19.

• WILD/LAB: groups of four wild-caught JUVENILES in 95 x 41 x 44 cm 170 L aquaria with gravel and artificial vegetation, separated from ADULTS by a net. 0+ JUVENILES from lake Fiskjön, Sweden, with higher predation risk through cannibalism spent less time in the open than 1+ JUVENILES with lower risk. 0+ JUVENILES from lake Ängersjön, Sweden, with higher cannibalism risk tended to spend longer in first feeding bout than 1+ JUVENILES with lower risk. Probably because risk for predation by pike Esox lucius is higher for 1+ JUVENILES. JUVENILES across ages and lakes had lower latency to start feeding on the second than first observation day indicating that JUVENILES realised the low risk of the restrained predator 19.
• For predator recognition and...
  ...importance of vision → D20,
  ...importance of olfaction → D21.

• Air exposure:
  • LAB: JUVENILES in 300 L tanks were caught, netted, and kept out of the water for 1 min. 30 min later, cortisol level had increased compared to control group (ca 120 versus 45 ng/mL) indicating stress. Decrease between observation time 30 min and 1 h, back to basal level at next observation time 4 h after handling. Tendency of increasing glucose levels with peak at 1 h after handling (55.9 versus ca 36 mg/dL) indicate increased energy expenditure. Increase in haematocrit with peak at 24 h after handling (21.2% versus 14.1%) indicates increase in oxygen transport efficiency to accommodate higher energy expenditure. Comparably high basal cortisol levels indicate lower adaptability to culture conditions 36.
  • LAB: 1+ JUVENILES of fourth captive generation of wild breeders in 100 L tanks that were drained and objected JUVENILES to 30 s air exposure. At 1 h after stressor, cortisol had increased compared to control group (57.3 versus 20 ng/mL) indicating stress. Back to control group levels at second observation time 6 h post stressor. At 1 and 6 h after stressor, glucose levels had increased compared to control group (1,150-1,243.7 versus 500-700 µg/mL). Back to control goup levels at third observation time 24 h post stressor. Decreased spleno-somatic index compared to control group (ca 0.06-0.08% versus 0.08-0.09%) at all observation times until 48 h post stressor indicates contracting spleen to provide blood with additional erythrocytes 39.

• LAB: transporting JUVENILES for 4 h at 8 kg/m³ increased cortisol level compared to control group (145.7 versus ca 50 ng/mL) for at least two days afterwards indicating stress. Decrease between observation day 2 and 7 after transport. Glucose increased with peak at day 2 after transport (70.9 versus 50 mg/dL) indicating increased energy expenditure; back to basal level at next observation day 7. Increase of haematocrit with peak at day 2 after transport (23.9% versus 18.4%) indicates increase in oxygen transport efficiency to accommodate higher energy expenditure. Decrease in osmolality until observation day 21 (ca 0.3 versus 0.35 mOsm/kg) indicates disturbed gill osmotic balance. Comparably high basal cortisol levels indicate lower adaptability to culture conditions 36.

• LAB: 1+ JUVENILES of first or fourth captive generation of wild breeders in 100 L tanks exposed to water emersion 3 times/week. On day 9, 48 h after the last stress event, lower cortisol levels in first generation JUVENILES compared to control group (4.7 versus 14.7 ng/mL); no difference in fourth generation (5.1-15.3 ng/mL). No differences on observation days 18 and 44 (6.0-24.9 ng/mL). No differences in glucose levels (385-727 µg/mL), spleno-somatic indices (0.05-0.06%), and serum lysozyme activity across generations and observation times. Increase in several proteins in serum indicate increased resistance to stressor. Results indicate no effect of domestication on physiological and immune responses to repeated handling 39.

• LAB: 0+ JUVENILES from wild-caught eggs in 100 dm³ tanks with either 22.7 °C or 16.6 °C water temperature. Tanks either undisturbed by wrapping in black plastic sheets, moderately disturbed by hand movements over the tank three times per day, or severely disturbed by hand movements three times per day and simulated cleaning with a brush once per day. After three rounds of three weeks each, lower feed intake (0.6-0.9 versus 0.8-1.1% group average weight/IND/day) and lower growth rate (0.3-0.5 versus 0.7-0.9) in severely compared to undisturbed tanks, independent of temperature; moderately disturbed tanks in between. Higher feed intake (0.8-1.1 versus 0.6-0.8% group average weight/IND/d) and higher growth rate (0.5-0.9 versus 0.3-0.7) under 22.7 than 16.6 °C. Decreasing feed intake (0.5-0.8 versus 0.9% group average weight/IND/d) and tendency of decreasing growth rate (0.4-0.6 versus 0.6-0.7) – lower at 16.6 compared to 22.7 °C – with increasing round indicating increased stress by long-term disturbance 37.
• LAB: ADULTS in 80 L aquarium with pebbles and plants were held under 12 h light (07:00-19:00 h), 12 h dark cycle and exposed to stress by people walking by at irregular times during the day. Over 32 d, almost no trigger of the self-feeder during photophase. Most frequent triggering (average 8 triggers/h) in first hour of scotophase (19:00-20:00 h). Thereafter decrease in triggers from 3 triggers/h in 20:00-21:00 h until around 1 trigger/h in remaining scotophase 8.

• 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) 45.

• To minimise pain reactions, enhance welfare, and reduce the impact on the quality of the fish meat, these are across species the most efficient stunning methods 45 46:
  a) percussive stunning (if immediately followed by exsanguination),
  b) electrical stunning (if immediately followed by exsanguination),
  c) anaesthetics (clove oil derivants),
  d) spiking (if immediately followed by exsanguination),
  e) shooting,
  but only a) and b) are adaptable to industrial scale, whereas c) is still not admitted for food purposes in Europe.
  Further research needed for a specific protocol for P. fluviatilis.