Investigation on health conditions of flounder and smelt in the Elbe estuary

Abstract

Since 1958 the occurrence of flounder (Platichthys flesus L.) and smelt (Osmerus eperlanus L.) in the lower River Elbe has shifted gradually toward the mouth of the river into the North Sea; this may be due to periodical deprivation of oxygen and fluctuating peaks of toxic nitrite concentrations. The interior organs of both fish species caught in the Elbe estuary were examined. Macroscopic inspections revealed discolouring of the liver to be most pronounced in specimens 2-3 years of age. Cross-sections of the liver demonstrated histopathological symptoms of oedematous degeneration in smelt, and extreme lipoid vacuolation in flounder increasing with size and age of the fishes. The intestine of both species investigated showed massive desquamation defects of the mucosa, occurring in smelts shortly after hatching, and in flounders after immigration into the estuary. The observations made suggest the influence of toxic compounds distributed in the aquatic environment on the health of both species. © 1980 Biologische Anstalt Helgoland.