|Fish diseases, signals for a diseased environment?|
Vethaak, A.D. (1986). Fish diseases, signals for a diseased environment?, in: Peet, G. (Ed.) The status of the North Sea Environment: Reasons for Concern, Proceedings of the 2nd North Sea Seminar 1986, Rotterdam, 1, 2, 3 October 1986: vol. 2. pp. 41-61
In: Peet, G. (Ed.) (1986). The status of the North Sea Environment: Reasons for Concern, Proceedings of the 2nd North Sea Seminar 1986, Rotterdam, 1, 2, 3 October 1986: vol. 2. Werkgroep Noordzee: Amsterdam. ISBN 90-70643-03-0. 351 pp., more
In recent years, the subject of fish diseases in relation to pollution has received more and more attention in research on the quality of the North Sea environment. On the basis of laboratory experiments, there is reason to believe that the introduction of toxic substances actually does have a negative effect on the health of fish populations in the North Sea ecosystems. However, conclusive evidence from the field is not yet available. Methodological uncertainties and the difficulty of separating natural disease causing factors from pollutional ones form the greatest problems for research. In general, the data base of fish disease occurrence in the North Sea is inadequate. Many of the investigations, in particular, are still incomplete because of the lack of chemical and microbiological parameters (thought to be) associated with the observed disease levels. Nevertheless, there are presently enough indications and circumstantial evidence to link some fish diseases with environmental deterioration in certain areas of the North Sea. To illustrate this, the results of our investigations (of the Dutch situation) have been summarized. These findings support the case for a relationship between pollution and the prevalence of diseases in adult flatfish from the Dutch coast (flounder -Platichtys flesus and dab- Limanda limanda). The first results over a three-year period (1983-86) reveal the presence of epizootic liver neoplasms (tumours), and the greater prevalences of several viral skin diseases (lymphocystis and epidermal hyperplasia/papilloma) and bacterial skin diseases (ulcers and fin rot) in the two flatfish species from the contaminated areas. The presence of liver tumours may be directly related to specific environmental contaminants and, in the case of viral and bacterial skin diseases, there are strong suspicions that there is an (in)direct relationship with the total pollution load of the water. Our findings certainly suggest that there is real cause for concern, particularly in regard to the observed liver tumours. It is concluded that the limited amount of knowledge about fish diseases does not permit an adequate assessment of the current situation or future problems regarding the health of marine fish populations.