Epidemiology of lymphocystis, epidermal papilloma and skin ulcers in common dab Limanda limanda along the west coast of Denmark

Abstract

A survey of fish diseases in the common dab Limanda limanda L. was conducted in 4 areas (the German Bight, 2 areas along the west coast of Denmark and the Skagerrak) in May during the years 1983 to 1993. A total of 53302 dab were examined for the presence of the diseases lyrnphocystis, epldermal papilloma and skin ulcers. The present study describes long-term variations in the prevalence of these 3 chseases. The German Bight 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 Bight showed a peak value of 9 4 % in 1988 and skln ulcers in the Skagerrak a peak of 4.4 % In 1989. Areas in the German Bight 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 papllloma in dab in the Kattegat. In 1988, the prevalence of lymphocystis and epidermal papllloma 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.

Regional patterns in prevalence of principal external diseases of dab Limanda limanda in the North Sea and adjacent areas 1992-1997

“…Prevalence rates in the present paper corresponded to those reported by Mellergaard & Nielsen (1997), who found between 4.5 and 12.8% infection in the German Bight between 1983 and 1992 (average in our study 10%). Figures reported by van Banning (1987) and Möller (1979) were consistently lower.…”

“…For ulceration, differences existed for some of the areas studied by Mellergaard & Nielsen (1997) but were absent during our present study, a finding also published by Wolthaus (1984a,b) for German Bight dab. There are no obvious explanations for these differences.…”

“…While Möller (1979) did not find differences for lymphocystis and van Banning (1987) did not expect sex-linked differences in his results, others like Wolthaus (1984a), Vethaak et al (1992) and Mellergaard & Nielsen (1997) found sex-related disease prevalence. The pattern emerging from the latter studies corresponds to our findings: lymphocystis is more frequent in females and epidermal papilloma are more frequent in males.…”

“…Bucke et al (1983b) found 1.1% of dab from Liverpool Bay to be afflicted with the disease. In their long-term study Mellergaard & Nielsen (1997) found up to 9.4% of dab from the German Bight with epidermal hyperplasia/papilloma and up to 7.9% of dab from the Horns Reef area to be afflicted. Again, infection rates of dab in the Skagerrak area were significantly lower than in most of the other areas.…”

“…Möller (1988) states that improving skill may cause investigators to detect increasing disease levels over time in their long-term series. On the other hand, it is known that regional, seasonal and annual differences of prevalence may account for a high variability (Wolthaus 1984b, Dethlefsen et al 1987, Mellergaard & Nielsen 1997. Most of the authors of the preceding studies more or less concentrated their investigation on their territorial waters, but there are exceptions such as Möller (1979), van Banning (1987 and Dethlefsen (e.g.…”