The development of marine environmental monitoring using fish diseases.

The difficulties in interpreting the biological significance of pollutants in the marine environment led to the recognition that natural indices reflecting chemical and physical changes are required. The close interaction between host, disease (including parasites) and environment indicates that change in disease patterns offers considerable potential as a natural monitoring system in this field. This problem was addressed by the Working Groups of the International Council for the Exploration of the Sea (ICES) in the early 1980s. Since then, a series of studies have provided internationally agreed recommendations on appropriate diseases to monitor, on sampling strategies and on guidelines for diagnosis, identification and data reporting. Research in Scottish waters has shown that parasites with complex life cycles and intermediate stages which are vulnerable to pollution can give a good indication of the dispersion of pollution from a point source. However, without good knowledge of the spatial, biological and temporal variations in the occurrence of fish diseases due to natural events, there are significant dangers in the interpretation of observed differences in disease as being pollution associated. As a general rule, it is probable that trends in disease differences will be of more use in environmental quality monitoring than would be differences in absolute levels of infection between different areas.