EPIDEMIOLOGY OF LYMPHOCYSTIS, EPIDERMAL PAPILLOMA AND SKIN ULCERS IN COMMON DAB LIMANDA-LIMANDA ALONG THE WEST-COAST OF DENMARK

A survey of fish diseases in the common dab Limanda limanda L. was con ducted in 4 areas (the German Eight, 2 areas along the west coast of D enmark and the Skagerrak) in May during the years 1983 to 1993. A tota l of 53 302 dab were examined for the presence of the diseases lymphoc ystis, epidermal papilloma and skin ulcers. The present study describe s long-term variations in the prevalence of these 3 diseases. The Germ an Eight and the 2 areas along the west coast of Denmark showed signif icant similarities in the temporal trend of the diseases investigated with peaks in 1985 and 1988 for both lymphocystis and epidermal papill oma. A similar trend was not observed in the Skagerrak. Skin ulceratio ns did not reveal any specific temporal trends in any of the 4 areas. The highest prevalence of lymphocystis was observed in the most offsho re area along the Danish west coast with a peak value of 14.9% in 1988 ; epidermal papilloma in the German Eight showed a peak value of 9.4% in 1988 and skin ulcers in the Skagerrak a peak of 4.4 % in 1989. Area s in the German Eight and along the west coast of Denmark had suffered from oxygen deficiency in late summer during the years 1981 to 1983. These events may have been an important factor triggering the outbreak of lymphocystis and epidermal papilloma, as the prevalence of these d iseases increased from 1983 until 1985 followed by a decline until 198 8. Although it was not possible to establish significant correlations between the oxygen levels at the bottom and the disease prevalence in the present case, the disease pattern showed evident similarities with formerly described oxygen deficiency-induced outbreaks of lymphocysti s and epidermal papilloma in dab in the Kattegat. In 1988, the prevale nce of lymphocystis and epidermal papilloma increased significantly wi thout any apparent reason. The disease pattern observed in the Skagerr ak differed significantly from the other 3 areas with skin ulcerations being the most prevalent disease. A part of the explanation for this may be that the Skagerrak has not suffered from the same impaired envi ronmental conditions as the other areas.