The European perch belongs to the Percidae family within the order of the Perciformes. Originally, this freshwater species can be found in inland waters of northern, central, and eastern Europe, including Scotland and England, but has been introduced to inland waters around the globe. The species is also able to cope with brackish water near coasts and with temperatures between 6 and 28 centigrades, 13 to 14 centigrades being the lower limit for growth.
Living mainly in the water column, European perch are opportunistic in choice of substrate. Everything from sand to mud to rocks and to tree roots or branches seems fine for them, with or without plants. For spawning, however, substrate of some kind is needed, as eggs are attached to it. There is some experimental evidence that shelter is needed.
As to the space European perch need, findings on home range and migration are lacking, with a doubt on migratory need for spawning, whereas need of depth ranges from 0 to 19 m, depending on the temperature: the lower the deeper. In nature, European perch can be found in co-existence with Largemouth bass, Brown trout, Bullhead catfish, Common carp, European and Short-finned eel, the Coregonus peled, and the Tench.
Photo: Thomas Hölzl, www.fisch-fotos.de
European perch can reach age up to 15 years, max. 45 cm total length and max. weight of 880 g. Males can reach maturity already in their first, females in their second year of life, having reached at least 6 cm total length and 9 g weight. In general, males seem to grow faster in the first one to two years, after which females grow faster.
In nature, European perch spawn in winter or spring, at temperatures between 11 and 22 centigrades, in depths between 0 and 12 m. The mating system seems to be polyandrous. Courtship lasts about 30 minutes. The female encircles with increasing speed the substrate item where the eggs are to be attached. One male follows her while other males observe the scene in order to replace the forerunner if possible. The female releases a single egg strand, 33,000 to 146,000 eggs per kilogramme of body weight; simultaneously the male(s) release(s) the milt.
European perch are carnivorous, feeding on increasingly larger prey as they grow. Their diet varies widely according to age and season, from zooplankton and insects to crustaceans, and more fish with increasing age. They seek for prey mainly at dusk, partly at dawn, in littoral zones, snipping item by item. At night, they reduce activity, whereas at daytime they try to avoid high light intensity.
The species’ visible spectrum in laboratory experiments is mainly green, red, and also violet. Vision seems to be the most important sense to recognise predators, followed by olfaction. European perch are hearing generalists, they detect a narrow bandwidth of sound frequencies (<0.1-30 Hz).
Experiments show cognitive abilities like learning to associate a stimulus to a response, learning to manage a self-feeder, or recognising predators. There are no findings so far on communication among individuals, on self concept, personality and coping styles, and on emotion-like states.
European perch live in shoals, juveniles and adults in spawning season also in schools, but there are no findings available on the number of individuals involved and the spatial expansion of their aggregation.
Aggression: no findings, but cannibalistic incidences are reported in the wild. Laboratory findings indicate a linear hierarchy in small groups, defence of shelter and higher feed intake by dominant juveniles, whereas subordinates hardly move and avoid contact with dominant individuals.
The farming of European perch has emerged over the past decades and has become an important part of aquaculture in Europe in recent years, according to the European Aquaculture Society. However, the reproduction of the species is still challenging. It was a Swiss biologist who first managed to fully close the reproduction cycle, delivering fingerlings to a Swiss farm.
However, still 60 times more European perch stem from fishing than from farming.
Low energy X-rays (mastography) are used to control the quality of farmed perch (Perca fluviatilis) fingerlings at Valperca, the first aquaculture facility to produce 100% Swiss grown perch.(Photo: Mariusnicolini / Wikimedia Commons)
Farming of European perch is increasing despite the fact that – as explained above – many aspects of the species’ biology are still not understood. The low FishEthoScore of the species is mainly due to thebig gap of knowledge on the following issues: lack of findings in nature on home range, migration, aggression (so far found in experiments, also for feed competition), and numbers and expansion of shoals and schools. Further research is needed on both natural behaviour and physiological effects of farming practices in order to provide recommendations for improving fish welfare.
In addition, there is doubt to what extent improved farming conditions could sufficiently cope with the species’ need for depth and substrate as well as with its proneness to stress, especially at stocking densities above 25 kg/m3, and by handling, with mortalities in spawning season up to 10% in males and 17% in females.
Finally, the welfare of European perch is impaired under common farming practices by lack of a protocol for humane slaughter and by manipulation of temperature and photoperiod to trigger reproduction and by stripping of eggs and milt. Also impaired is the welfare of wild fishes caught to be processed as fish meal and fish oil to feed farmed European perch as long as there is no alternative to forage fish in feeding.
There is potential for the improvement of the welfare of farmed European perch. Extensive farming in ponds and low stocking densities are simple measures for higher fish welfare and less stress. Under intensive farming conditions in tanks, substrate and shelter could add to fish welfare as well as avoiding manipulation in reproduction. The need for space could at least be met in the vertical dimension. Considering the species’ circadian rhythm and its preferred time of day for activity and rest will add to welfare.
Finally, the partial or even full replacement of feed components from forage fisheries would reduce the impairment of wild fish welfare.
Further research is needed, both on the senses and the natural behaviour of the species and on the effects of farming conditions, in order to provide more purposeful recommendations to improve farmed fish welfare.
For the time being, labels (i.e. seals of approval) are not helpful for clients who care for the welfare of farmed fish. The guidelines of organic labels are the ones most inclined to grant animal welfare, yet they define no tangible instructions. All other labels address animal health at best, but do not acknowledge all-encompassing aspects of animal welfare. That is to say that even fishes farmed under labels like organic, ASC, or Friend of the Sea, often live under the conditions of intensive animal husbandry. However there is some hope as several labels are currently studying the feasibility of integrating fish welfare into their certification schemes.
If we want to change the disregard for animal welfare, we need more of two things: ethological research and pressure from concerned consumers who want to eat respectfully-farmed fish.