Environmental Enrichment and its effects on Welfare in fish

Summary

Although public and consumer awareness is increasing fast in regard to welfare in captive fish; one often neglected aspect of fish welfare is the complexity of their holding environment. Increasing the complexity in any given way is termed environmental enrichment. Enriching the environment of fishes can have various positive effects on physiology, health, survival and therefore general welfare. However, it usually is also increasing labor through increasing maintenance and handling time and is lowering thus the efficiency. Fish welfare in general includes also the acceptance that fish can feel a certain degree of pain and should be considered, at least to a certain degree, sentient and conscious beings, which is scientifically still under serious debate.
Under the assumption that fish have the capabilities to feel pain and are, at least to a certain extent, conscious and sentient beings, the often neglected welfare‐aspect of environmental enrichment and its effects on fish under captive conditions are discussed in this review. This includes farmed fish for human consumption and restocking purposes (aquaculture) and fish kept for research. A definition of environmental enrichment is as well provided as a historical context, different enrichment types and the aims of environmental enrichment and areas of its application. Whether or not fish can feel pain is also debated.
An extensive table is included, providing natural micro‐, meso‐ and macrohabitat preferences of some important freshwater salmonids (rainbow and brown trout, Arctic char), Eurasian perch and common carp in different life stages (fry, juveniles, adults). Furthermore the environmental enrichment is considered under the perspective of in‐stream restorations and its effect on, primarily, salmonids in culture. Environmental enrichment includes physical structures added to the captive environment to provide increase the structural complexity while other forms of environmental enrichment may include sensory, social, nutritional or even occupational enrichment. The latter, however, is usually not of higher importance for fish. In the various research papers reviewed, it is obvious that environmental enrichment can provide several beneficial advantages although some negative effects have been observed too. Observations of environmental enrichment effects on a production or farm level are basically completely missing in the literature and therefore a large knowledge gap exists between laboratory studies and practical application. While several types of environmental enrichment have been adapted to aquaculture out of necessity, mainly in terms of reproduction success, little is known of environmental enrichment effects on fish welfare under production conditions and whether benefits may outweigh the drawbacks like increased installation costs or increased effort for maintenance.