Caging techniques for field exposures of fish to chemical contaminants.

The article reviews current state-of-the-art to conduct fish caging as an assessment and monitoring technique in aquatic toxicology. A multitude of scientific, practical and management factors influence and may restrict how field research is carried out. For many purposes the advantages of transplant fish caging outweigh the alternative methodologies of impact studies of xenobiotics. However, besides mortality, virtually no study has evaluated the physiological consequences of caging fish. It is not known how caging itself affects the responses of fishes to chemical pollution. The used caging densities are commonly too high. However, with the aid of variables describing physiological stress it is possible to evaluate stress-free caging for a given species, cage design, and experimental settings. Comparison of fish in cages to free-living counterparts or to fish in confirmed stress-free conditions are appropriate ways to evaluate the status of fishes used as references. An international harmonization and standardization of methods would widen the use of transplant caging of fish as a tool for environmental research and assessment.