Glochidia of the freshwater mussel,Anodonta anatina, affecting the anadromous European smelt (Osmerus eperlanus) from the Eider estuary, Germany

Abstract

During a 2‐year survey on external disease conditions of fish between January 1988 and December 1989, 0.2% of 40011 smelt,Osmerus eperlanus, from 30 stations in the German Wadden Sea and estuaries of tributary rivers, were infected with glochidia of the freshwater mussel Anodonta anatina. Seasonality was marked, with glochidia only being observed in March and April 1989, when prevalences were 37% and 15% respectively, in fish 10–20cm long at the most heavily infected site. A marked increase in prevalence in fish 15cm in length and longer, suggested that only temporarily resident spawning fish (as opposed to resident juveniles) were infected. Infection was almost exclusively restricted to the Eider estuary, where prevalence decreased with increasing salinity. It is concluded that the glochidia carried by smelt returning from their freshwater spawning sites in the Eider River to the sea would have died, thus representing a loss to the 1989 cohort of A. anatina from the Eider. The potential importance of the smelt–A. anatina relationship as indicator for the detection of (a) spawning mussel populations and of (b) possible ecological effects of climate changes is noted.