IMPACT OF OXYGEN DEFICIENCY ON THE DISEASE STATUS OF COMMON DAB LIMANDA-LIMANDA

An epidemiological survey of the fish diseases lymphocystis, epidermal papilloma and skin ulcers in common dab Limanda limanda L. was conduc ted in the southern Kattegat each year in May from 1984 to 1993. Durin g the period of investigation, severe oxygen depletion occurred in lat e summer 1986 and 1988. After the oxygen deficiency in 1986, the occur rence of lymphocystis and epidermal papilloma increased and peaked in 1989 with prevalences of 14.7 and 3.3%, respectively. The prevalence o f skin ulcers never exceeded 0.6%. The relative risk of contracting ly mphocystis increased significantly from 1987 to 1991 compared with 198 4 to 1986, the period prior to the severe oxygen depletion. A signific ant increase in the relative risk of contracting epidermal papilloma w as observed from 1987 to 1990. Females were 3 times more likely to con tract this disease than males. The relative risk of skin ulcers did no t change significantly during the investigation period. The prevalence of lymphocystis and epidermal papilloma was negatively correlated wit h the minimum oxygen levels measured in August and September the previ ous year; this negative correlation was significant (p < 0.05) for lym phocystis in September, while not for epidermal papilloma (p < 0.1). T he prevalence of lymphocystis and epidermal papilloma was significantl y correlated (p < 0.01). No significant correlation was observed betwe en stock density (expressed as catch per unit effort) and the diseases in question. It is probably the stress caused by the oxygen deficienc y - especially the sublethal levels - that triggered the outbreak of t he 2 viral diseases lymphocystis and epidermal papilloma.