• Escapes: rear only in environments where it naturally occurs D1 and prevent escapes. Else, escapees from fish farms may have negative or at most unpredictable influences on the local ecosystem. Prepare for sexual maturity (and thus spawning) from 0-2 years or 6-14 cm or 9-18 g on for males and 1-4 years or 10-20 cm or 23-126 g on for females D2 and take measures against spawning into the wild.

3.1 Substrate and/or shelter

• Substrate:
  • Substrate: no clear substrate preference D3. For the most natural solution, provide a range of rock sizes as well as sand and different kinds of vegetation.
  • For substrate and...
    ...nest building ➝ A1,
    ...occupation ➝ A2.
• Shelter or cover:
  • Cover: avoid complete cover in respect for the crepuscular rhythm A3.
  • Vegetation: ➝ Substrate. If high light intensities cannot be avoided, provide algae as cover D4.
  • Shelters: enrichment with e.g. a plastic tube that is open on one side probably increases the value for juveniles, but this may cause attacks and chases to establish territories D5. Further research needed to determine whether this holds also in farm environments and in groups with more than three individuals.

3.2 Photoperiod

• Photoperiod: given the distribution D1 D6, natural photoperiod is 6-18 hours, depending on the season. Provide access to natural (or at least simulated) photoperiod and daylight.
• Light intensity: avoid high light intensity or provide withdrawal opportunities like shelters or vegetation or algae A4, so that individuals are active throughout the day. Otherwise, they restrict activity to dawn and dusk D4.
  Provide light intensity of >1,000 lux for the visually predating European perch to insure proper feed intake and growth D7. If only lower intensities are possible, provide light Artemia nauplii in dark tanks or dark feed pellets in white tanks to improve visibility of feed and hence feed intake and growth D7. Further research needed to determine whether this holds also in farm environments.
• Light colour: no ethology-based recommendation definable so far.
• Resting period: respect the crepuscular rhythm of European perch and its resting period at night or in the dark D4. Although most likely not causing stress, refrain from nocturnal lighting >1 lux or photoperiod exceeding natural conditions, because it reduces melatonin production and impairs circadian melatonin rhythm D8 and we have not found studies reporting possible long-term effects on welfare ➝ fair-fish database's understanding of fish welfare.

3.3 Water parameters

• Temperature: no clear temperature preference, probably best kept at 20-23 °C D9 D10 D11. Below may mean lower growth D12 D11. Adjust temperature when you notice avoidance behaviour D13 D10. Implemented in aquaculture, temperatures >22 °C demand excellent oxygen levels D14 and a fine-tuned flow-through system to prevent bacterial load.
  For temperature and spawning ➝ A1.
• Water velocity: no ethology-based recommendation definable so far.
• Oxygen: in the wild, oxygen level is at 6-9 mg/L D14. Further research needed. Maintain oxygen level that ensures welfare depending on temperature (➝ Temperature) and stocking density (➝ A5).
• Salinity: given the distribution, natural salinity is at fresh- or brackish water level D1 D6 D15. Maintain a salinity level that ensures welfare.
• pH: no ethology-based recommendation definable so far.
• Turbidity: in the wild, water transparency is at 1.1-7.5 m Secchi depth D16. For the most natural solution, maintain turbidity at this range. Further research needed.

3.4 Swimming space (distance, depth)

• Distance: no ethology-based recommendation definable so far. Provide enough space, bearing in mind the planned stocking density A5.
• Depth:
  • Depth range: in the wild, found at 0-18.5 m D10. Provide at least 6 m, ideally up to 19 m, bearing in mind the planned stocking density A5. Individuals should be able to choose swimming depths according to life stage and status D17.
    For depth and spawning ➝ A1.
  • Flight: provide enough depth for the flight response to light D10.
  • Temperature layers: in habitats with water layers with different temperatures, prepare for individuals migrating to layers with preferred temperatures D9 D10, and avoid crowding in these layers by providing enough space.

• Alternative species: carnivorous D18, trophic level 4.4 D19. If you have not yet established a European perch farm, you might consider to opt for a species that can be fed without or with much less fish meal and fish oil in order not to contribute to overfishing by your business D20.
• Protein substitution: if you run a European perch farm already, try to substitute protein feed components that have so far been derived from wild fish catch, while taking care to provide your fishes with a species-appropriate feed D18:
  • Invite a feed mill and other fish farmers in your country to jointly establish a recycling syndicate that converts the remainders and the offcuts of fish processing into fish meal and fish oil, separating the production line corresponding to the species of origin in order to avoid cannibalism ➝ fair-fish farm directives (point 6).
  • Inform yourself about commercially tested substitutes for fish meal and fish oil, like insect or worm meal or soy, with an appropriate amino and fatty acid spectrum.
• Feed delivery:
  • Feeding frequency and time, feed delivery, self-feeders: visual feeder D7, snaps food in the littoral D21, mostly crepuscular D4. Refrain from feeding during night time in respect for European perch's natural resting period. Alternatively, install a self-feeder and make sure all European perch adapt to it. No ethology-based recommendation definable so far on feeding frequency as well as speed and pattern of feed delivery. Note postponed feeding at night time given stress D11 and decreased feeding at temperatures <16.6 °C D13. For the latter, reduce the amount of food offered accordingly (if not using a self-feeder).
  • Food competition: make sure to provide sufficient feed from ca 4 days after hatching on D22. Avoid high energy food (e.g., fish larvae) for larvae, fry, and 0+ juveniles, because in case of food competition only part of the population will take advantage of it, increasing size bimodality and giving rise to cannibalism D23. Providing larvae, fry, and 0+ juveniles with Zooplankton and – from ca day 40 on – macroinvertebrates potentially results in smaller size differences and less cannibalism D23. Further research needed.
• Particle size: no ethology-based recommendation definable so far.
• Feed enrichment: no ethology-based recommendation definable so far.

• Maturity: in the wild, matures from the first year on D2. Even if manipulating time of maturity were possible, refrain from it, as we have not found studies reporting possible long-term effects on welfare ➝ fair-fish database's understanding of fish welfare.
• Manipulating sex: even if manipulating sex were possible, refrain from it, as we have not found studies reporting possible long-term effects on welfare ➝ fair-fish database's understanding of fish welfare.
• Sex ratio: no ethology-based recommendation definable so far. Although females develop faster and grow bigger than males D24, refrain from monosex (female-only) groups, as females do not necessarily grow faster or heavier than mixed-sex groups until 87 days, do not differ in cannibalism from mixed-sex groups D23, and as we have not found studies reporting possible long-term effects on welfare ➝ fair-fish database's understanding of fish welfare.
• Size-grading: when in small groups, better size-grade juveniles, otherwise they aggressively establish a social hierarchy D25. Further research needed for behaviour in larger groups.
• Other effects on growth:
  • Polyculture: in the wild, co-exists with Bass, Brown trout, Bullhead catfish, Carp, Eel, Peled, Tench D26. Further research needed for benefits of polyculture.
• Deformities and malformations: no ethology-based recommendation definable so far.
• For growth and...
  ...light intensity ➝ A3,
  ...tank colour ➝ A3,
  ...water temperature ➝ A6,
  ...disturbance ➝ A7.

• Nest building: lake spawner D27 on gravel or at submerged vegetation D28. For the most natural solution, provide a range of substrate.
• Courtship, mating: respect courtship behaviour in which female circles water plants for up to 30 minutes and several males attend D29 D30.
• Spawning conditions: for spawning substrate ➝ Nest building (above). Respect natural spawning season in winter to spring at temperatures of 11-22 °C D28. Shelter spawning tanks and ponds from wind and wave action to protect egg strands from hydrodynamic damage D28. Then, 0.5 m depth might be sufficient. If wind protection is impossible, provide 3-12 m depth D28. No ethology-based recommendation definable on salinity and water velocity. Hints that survival and cannibalism rate are heritable D23, so select breeding individuals by the highest survival and lowest cannibalism rate. In the wild, male:female ratio resulting in spawning is 1:4.6 D31. Further research needed. For the most natural solution, maintain this ratio.
• Fecundity: in the wild, 32,000-146,000 eggs per kg body weight D32. Even if manipulating fecundity were possible, refrain from it, as we have not found studies reporting possible long-term effects on welfare ➝ fair-fish database's understanding of fish welfare.

• Maximum: the businessplan should be calculated on the basis of a maximum stocking density that will never exceed the tolerable maximum with regard to fish welfare.
• Stocking:
  • Stocking larvae: no ethology-based recommendation definable so far.
  • Stocking juveniles and adults: in the wild, shoal from body size of average ca 3.2 cm on at 0.1-8.1 individuals/m; larger juveniles and adults also in schools D33. In lakes, 30-3,500 juveniles/ha D34. Hints of increased cannibalism when fry are kept at lower than 10,000 individuals/cage or juveniles at lower than 25-30 kg/m³ D35. Further research needed.
• Restriction:
  • Habitat structuring: consider loss of space due to structures inside and outside the system A4 and calculate density accordingly.
  • Environmental conditions: in the wild, displays a large variability in preferences for substrate D3, water temperature D9, turbidity D16, and depth D10. Consider increased density at places with preferential conditions A4 A6 A8 and calculate density accordingly.
  • Aggregation: in the wild, individuals build shoals or schools D33. Consider increased density at places due to formation of shoals or schools and calculate density accordingly.
  • Aggression: choose density given displayed aggression between higher frequency of cannibalism at low density and higher number of natural deaths at higher density and adjust accordingly D23 D36. Further research needed. Aggression may entail displays, attacks, chases, nips D5 as well as cannibalism D23.
  • Territoriality: no ethology-based recommendation definable so far.
• Interaction: as show the above influence factors, stocking density is only one part of a complex interaction of factors to affect welfare. It should never be considered isolatedly.

• Food search: provide sand, mud, or rocks so that individuals may search for food D3 D21.
• Challenges: if after decreasing stress A7 and providing everything welfare assuring, you still notice stereotypical behaviour, vacuum activities, sadness, then provide mental challenges, diversion, variety, and check reactions.

9.1 Handling

• Stress coping styles: individuals differ in their ability to cope with stress, so assume the smallest common denominator during stressful situations and handle with care and high efficiency.
• Stress measurement:
  • Physiological stress indicators: plasma cortisol exceeding 14.7-50 ng/mL D37 D38 D39, glucose exceeding 36-50 mg/dL D37 D38 or 385-727 µg/mL D37 D39, haematocrit exceeding 14.1-18.4% D37 D38 indicates stress.
  • Abnormal behaviour: after, e.g., changing parameters, check for behaviour deviating from the norm D40 D41 D21 D4 D42 D10 D43 D24 D29 D30 D44 D32 D33 D25 D36 D45.
• Stress reduction:
  • Noise: hearing sensitivity is unaffected by noise of up to 100 dB D46. Still, noise should not exceed levels of natural freshwater habitats (40-100 dB).
  • Directing individuals: to direct individuals in the habitat (e.g., for cleaning purposes), make use of European perch's ability to be conditionable D45 D47 to reduce stress.
  • Cage submergence: no ethology-based recommendation definable so far.
  • Pain treatment: no ethology-based recommendation definable so far.
  • Handling: handle as carefully as possible, as it causes stress D37. After air exposure for one minute, let recuperate for at least one hour D37.
  • Confinement: no ethology-based recommendation definable so far.
  • Crowding: no ethology-based recommendation definable so far.
  • Transport: avoid live transport, as it causes stress D38. If unavoidable, after transport for four hours, let recuperate for at least two days D38.
  • Disturbance: keep disturbances (e.g. passing by, hand movements, cleaning) to a minimum (or restrict view to areas where disturbances could occur), as they decrease feed intake and growth – even more so if done repeatedly D11. Further research needed to determine whether this holds also in farm environments.
  • For stress reduction and...
    ...cover ➝ A4,
    ...nocturnal lighting ➝ A3,
    ...feed delivery➝ A9,
    ...stocking density ➝ A5,
    ...stunning ➝ A10.

9.2 Slaughter

• Stunning rules: render individuals unconscious as fast as possible and make sure stunning worked and they cannot recover D48.
• Stunning methods: prefer percussive stunning, because it renders individuals unconscious fast if administered correctly and with sufficient force D49. Alternatively, use electrical stunning. Further research needed for a specific protocol.
• Slaughter methods: bleed or gut individuals immediately after stunning, i.e. while unconscious.

• Certification: fair-fish international association warmly advises to follow one of the established certification schemes in aquaculture in order to improve the sustainability of aquafarming. Adhering to the principles of one of these schemes, however, does not result in animal welfare by itself, because all these schemes do not treat animal welfare as a core issue or as an issue at all. Therefore the FishEthoBase has been designed as a complement to any of the established certification schemes. May it help practitioners to improve the living of the animals they farm based on best scientific evidence at hand.
• To give you a short overview of the most established schemes, we present them below in descending order of their attention for animal welfare (which is not necessarily the order of their sustainability performance):
  • The fair-fish farm directives are not present on the market, we cite them here as a benchmark. The directives address fish welfare directly by being committed to FishEthoBase: for each species, specific guidelines are to be developed mirroring the recommendations of FishEthoBase; species not yet described by FishEthoBase cannot be certified. In addition, the directives address a solution path for the problem of species-appropriate feeding without contributing to overfishing.
  • The Naturland Standards for Organic Aquaculture (Version 06/2018) generally address  animal welfare with words similar to the fair-fish approach: "The husbandry conditions must take the specific needs of each species into account as far as possible (…) and enable the animal to behave in a way natural to the species; this refers, in particular, to behavioural needs regarding movement, resting and feeding as well as social and reproduction habits. The husbandry systems shall be designed in this respect, e.g. with regard to stocking density, soil, shelter, shade and flow conditions."
    In the details, however, the standards scarcely indicate tangible directives for European perch, except for percids in general when kept in sea cages: no grow-out in artificial tanks, stocking density limited to 10 kg fish/m³ max. Live transportation is limited to 10 hours max, to 1 kg/8 L max, and to adequate provision of oxygen, with water exchange after six hours.
  • The GAA-BAP Finfish and Crustacean Farms Standard (Issue 2, September 2014) directly addresses animal welfare: "Producers shall demonstrate that all operations on farms are designed and operated with animal welfare in mind." Farms shall "provide well-designed facilities", "minimize stressful situations" and train staff "to provide appropriate levels of husbandry". Yet the standard does not provide tangible and detailed instructions for the practitioner, let alone species-specific directives.
    In September 2017, GAA-BAP received a grant from the Open Philanthropy Project to develop best practices and proposed animal welfare standards for salmonids, tilapia, and channel catfish. Thus, fish welfare on GAA-BAP certified farms might become more tangible in the future, eventually also for European perch at a later date.
  • The GlobalG.A.P. Aquaculture Standard (Version 4.0, March 2013) "sets criteria for legal compliance, for food safety, worker occupational health and safety, animal welfare, and environmental and ecological care." The inspection form includes criteria like "Is the farm management able to explain how they fulfil their legal obligations with respect to animal welfare?", "If brood fish are stripped, this should be done with the consideration of the animal's welfare." or "Is a risk assessment for animal welfare undertaken?". The scheme claims that 45 out of a total of 249 control points cover animal protection, yet it does not provide any tangible directives, let alone species-specific directives..
  • The ASC Aquaculture Stewardship Council. The ASC standards address fish welfare only indirectly, as a function of a “minimum average growth rate" per day, a "maximum fish density at any time", and a "maximum average real percentage mortality". fair-fish sees animal welfare as an intrinsic value, not just as a result of optimising neighbouring values like health care and management procedures. 
    There is no ASC standard for European perch so far.
    In November 2017, ASC received a grant from the Open Philanthropy Project to develop an evidence-based fish welfare standard that is applicable to all ASC-certified species. ASC intends to share its approach to fish welfare with all farms engaged with the ASC program and encourage adoption of it, which means that the fish welfare standard will function as a non-mandatory add-on to the ASC certification.
  • The Friend of the Sea (FOS) Standards for freshwater aquaculture of fish (revised October 2016) do not even address animal health or animal welfare issues.
    In May 2017 however, FOS signed a Memory of Understanding with fair-fish international on developing fish welfare criteria for the FOS standard. In November 2017 fair-fish international association received a grant from the Open Philanthropy Project to assess the welfare of fish on FOS certified farms, develop farm-specific recommendations, and to develop animal welfare criteria for the FOS standard. Thus, fish welfare on FOS certified farms might become tangible in the future.