Dr. Murai Éva szerk.: Parasitologia Hungarica 25. (Budapest, 1992)

In one plankton sample from a fish pond we found procercoids in the body cavity (hemocoel) of Diaptomus sp. (Copepoda) (Fig. 2). They were numerous (about 35 larvae) and measured 0.1 mm approximately. In this pond the yield of fingerling production was low and mortality occurred. Procercoids were also often seen in the intestine of fish fry, as they were just migrating out of partially digested planktonic copepods. In young fry, plerocercoid invasion caused heavy histopathological changes. The intestinal wall became thin, the mucosa seemed to have become atrophic. The plicae of the mucosa were low, and mucus cells could scarcely be found in it. In the submucosa, the connective tissue layer thickened, the number of lymphocytes between the different layers increased. The loose fibrous connective tissue under the serosa contained a large number of mononuclear imflammatory cells with eccentric nucleus, and eosinophilic granulation could be observed in the cytoplasm. The intestinal lumen was visibly deformed (Fig. 3). The liver was also deformed, due to the pressure exerted by the numerous parasitic cysts surrounding the organ (Fig. 4). Haemorrhages were also seen in different layers of the intestinal wall. DISCUSSION Apart from Thatcher's work (1981), no data are available on plerocercoid infestation of fishes in the Brazilian Northeast. Among the most dominant cestodes of North America, Mitchell and Hoffman (1980) discussed the life cycle of Proteocephalus ambloplitis in black bass. We belive that the life cycle of Proteocephalidea from tucunare is very similar. The adult tapeworms live in the intestine of tucunare. Gravid segments with fully developed eggs are shed with the faeces. When the segments are destroyed by scavengers, the eggs are released and eaten by copepods (first intermediate host). The oncospheres, which are liberated in the intestine of the copepod, burrow into the hemocoel and develop into procercoids. When the copepod is eaten by a small fish the procercoids move through the intestine into the abdominal cavity and become encapsulated. The parasite develop into plerocercoids with scoleces resembling those of the adult. If this second intermediate host is eaten by the piscivorous fish tucunare, the final host, plerocercoids mature in its intestine and produce eggs. A similar deviation from the usual life history as that described for P. ambloplitis from the black bass (Mitchell and Hoffman 1980) occurs also in tucunare. If the plerocercoids are not fully developed when eaten by the final host, they may again burrow through the intestinal wall and inhabit the abdominal cavity. We suppose that plerocercoids found in many fishes in the Brazilian Northeast originate from proteocephalid cestodes of tucunare. According to the data found, there are several proteocephalids parasitizing tucunare. Diesing described a tapeworm from this fish species in 1850 (cit. Woodland 1935) under the name of Proteocephalus macrophallus. Later Woodland (1935) stated