A survey of fish diseases in the common dab Limanda limanda L. was conducted in 4 areas (the German Eight, 2 areas along the west coast of Denmark and the Skagerrak) in May during the years 1983 to 1993. A total of 53 302 dab were examined for the presence of the diseases lymphocystis, epidermal papilloma and skin ulcers. The present study describes long-term variations in the prevalence of these 3 diseases. The German Eight and the 2 areas along the west coast of Denmark showed significant similarities in the temporal trend of the diseases investigated with peaks in 1985 and 1988 for both lymphocystis and epidermal papilloma. A similar trend was not observed in the Skagerrak. Skin ulcerations did not reveal any specific temporal trends in any of the 4 areas. The highest prevalence of lymphocystis was observed in the most offshore 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. Areas 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 diseases increased from 1983 until 1985 followed by a decline until 1988. 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 lymphocystis and epidermal papilloma in dab in the Kattegat. In 1988, the prevalence of lymphocystis and epidermal papilloma increased significantly without any apparent reason. The disease pattern observed in the Skagerrak 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 environmental conditions as the other areas.
Diseases of Aquatic Organisms, 1997, Vol 30, Issue 2, p. 151-163