Parasitation with Pseudoterranova decipiens (Nematoda) influences the survival rate of the European smelt Osmerus eperlanus retained by a screen wall of a nuclear power plant.

A total of 354 adult European smelts Osmerus eperlanus (L.) were tested for their ability to survive the screen system of the cooling water inflow of a power plant. With increasing number of musculature parasitic third-stage larvae of Pseudoterranova decipiens, the survival rate of O. eperlanus decreased while the total number of externally visible injuries as well as the number of seriously injured specimens increased. The results indicate that even a single specimen of P. decipiens influences resistance and stamina and affects overall mortality of 7 to 20 cm long smelts. The initial effect of the parasites is to reduce swimming speed of infested fish, which leads to more frequent contact of these fish with the fine meshed screen of the cooling water inlet before they are removed by the automatic cleaning system. If the separated fishes are returned to the main stream, it becomes apparent that the cooling water inflow selectively reduces the number of living parasitised smelt in the area. Thus, the number of parasitic third-stage P. decipiens larvae in the local smelt population which are able to complete their life-cycle is also reduced. P. decipiens makes infested smelt more susceptible to negative anthropogenic influences such as cooling water intake or trawl fisheries.