Parasite transfer from crustacean to fish hosts in the Lübeck Bight, SW Baltic Sea

Abstract

Four helminth parasites out of 19 species found in the Lübeck Bight, Baltic Sea, were chosen for investigations on the transfer from invertebrate to small-sized fish hosts: larvae of the tapeworms Schistocephalus sp. and Bothriocephalus sp. (Cestoda) living in planktonic copepods as primary hosts;Podocotyle atomon (Digenea) and Hysterothylacium sp. (Nematoda) were found in benthic crustaceans, especially Gammarus spp. These hosts were the prey of 3 gobiid fishes, Gobiusculus flavescens (feeding mainly on plankton), Pomatoschistus minutus (preferring benthos), and P. pictus (feeding more on plankton than benthos). Because the fishes selected smaller sizes of crustaceans, they ingested all stages of the copepods but only the smaller-sized groups of gammarids which were often less infested by parasites. In order to evaluate the probability for a fish to be parasitized by a helminth, an infestation potential index (IP) was calculated. Podocotyle atomon and Hysterothylacium sp. revealed an IP which was far lower in gobies than expected when the prevalences of the previous hosts were taken into consideration. The IP of tapeworm larvae was mainly influenced by the feeding pressure of the gobiid predators, which might change with developmental stage and season. It is concluded that parasite transfer to the next host decreases when sizes of prey and predator differ only moderately. This mechanism can reduce the numbers of parasites transferred to less suitable or wrong hosts. © 1994 Biologische Anstalt Helgoland, Hamburg.