Common diseases and parasites of fish in the North Atlantic: Training guide for identification

During the past 20 years, there has been an increasing number of field surveys investigating the occurrence and distribution of fish diseases as a tool for monitoring the effects of environmental changes, including marine pollution. Fish diseases are considered to be an appropriate indicator in this context because the outbreak of a disease represents an end-point of biological significance integrating all environmental factors affecting fish health. In the beginning of the 1980s it was felt, in the scientific community involved in fish disease studies, that it would be useful on an international basis to compare and combine the results of the different groups studying fish diseases. This would then present an overall picture and evaluation of the health status of fish populations in the study areas. However, it was soon realized that the results on disease prevalences available for different fish species and different areas were often derived from studies using non-standardized methodologies; thus, the results were not comparable. To meet this problem, two ICES Sea-going Workshops on the Methodology of Fish Disease Surveys were held, in 1984 and 1988, initiated by the ICES Working Group on Pathology and Diseases of Marine Organisms (WGPDMO) (Dethlefsen et al., 1986; ICES, 1989). The major aims of these workshops were to set up recommendations for standardized methods for sampling, diagnosis, and reporting of fish diseases. Such standardization would enable investigators to meet minimum requirements which would allow international comparisons of long-term trends in spatial and temporal distribution patterns. Arising from the workshops, the WGPDMO decided in 1990 that it would be useful to produce this Training Guide for the Identification of Common Diseases and Parasites of Fish in the North Atlantic, which should be published in a way that it could be used during work on board research vessels or under other field conditions. The objectives of this Training Guide are to summarize the recommendations and conclusions of the Sea-going Workshops and, in order to enable a proper diagnosis, to present a set of photographs showing selected examples of common diseases in major fish species of the North Atlantic. This Training Guide gives advice to specialists and non-specialists on the following topics: • fish species suitable for disease monitoring; • sampling procedures; • disease examination procedures; • diseases useful for monitoring purposes and their diagnosis and classification; • reporting of results; • statistical methods applicable for data analysis. The procedures recommended and diseases illustrated in this Training Guide are mainly based on bottom trawl catches from the North Sea. However, investigators should be able to adapt the model to their own local situations, if necessary.