Occurence and biology of the trematodes cotylurus (ichthycotylurus) erraticus, C. (I.) variegatus and C. (I.) platycephalus (digenea: strigeidae) in the Netherlands

Abstract

The detection that gulls had died a hyperinfection with Cotylurus species, did start this study on distribution, life-cyle and ecology of these parasites in the Netherlands. Three species were found: C. erraticus (Rud., 1809), C. variegatus (Crepl., 1825) and C. platycephalus (Crepl., 1825). The first intermediate host is Valvata piscinalis, the rate of infection was about 3%. Infected snails are sterile and somewhat larger and had in our samples a higher mortality rate than non-infected snails. A description is given of the cercaria of Cotylurus erraticus from naturally and experimentally infected snails. Differences are noted with the description of the cercaria of C. erraticus from America. It seems doubtful if both are conspecific. Metacercariae occurred especially in fishers fromt eh IJsselmer, a freshwater lake, newly formed after closing of the Zuiderzee in 1932. Metacercariae of Cotylurus erraticus were found in Osmerus eperlanus and Salmo gairdneri, mainly in the pericardium. C. variegatus was found in Gymnocephalus cernua, Stizostedion lucioperca and Perca fluviatilis, mainly on the wall of the swimbladder. C. platycephalus was found in Gymnocephalus cernua, Stizostedion lucioperca, Abramis brama, Leuciscus cephalus and for a small percentage also in Osmerus eperlanus and Rutilus rutilus, especially in pericardium and mesentery. The rate of infection of Osmerus eperlanus with Cotylurus erraticus and Gymnocephalus cernua with C. variegatus and C. platycephalus in the IJsselmeer amounted to nearly 100%, with many tens of cysts per fish. In other inland waters this rate was low or nihil. Infected fishes from the IJsselmeer may enter the Wadden Sea, especially in winter, by the discharge of water from the IJsselmeer through the sluices. Some fish-eating birds, in particular gulls, acted as final hosts. Heavy infections with Cotylurus variegatus and C. platycephalus were often found to be lethal. C. erraticus seems less pathogenic. Repeated infection may lead to some kind of immunity. The small C. erraticus and the larger C. variegatus live in the same part of the intestine, the large C. platycephalus on the other hand lives in the cloaca of the final host. The distribution of the first intermediate host ( Valvata piscinalis) makes the cercariae to be limited to large fresh water bodies. From here fishes may transport the metacercariae over considerable distances and even to the sea. Of course the distribution of adults through birds is even wider.