Remarks on the morphology, site of infection and validity of some coccidian species from fish.

The morphological identification of carpelli-type oocysts of Goussia species parasitizing the gut of different cyprinids is unreliable. Species similar in shape and size can be differentiated only by cross-infection experiments. Goussia scardinii (Pellérdy et Molnár, 1968), developing in the renal tubules of cyprinids, is a synonym of Goussia leucisci (Shulman et Zaika, 1964). The morphology and location hitherto assumed to be species characteristics of G. scardinii can be explained by the aging of oocysts and the type of host reaction. Eimeria rutili Dogiel et Bychowsky, 1938 is a coccidian parasite occurring in various organs of the roach. Its oocysts can be found in the blood vessels and, thus, also in the gill capillaries. Eimeria branchiphila Dyková, Lom et Grupcheva, 1983, described from blood vessels of the gills of the same fish species, should be regarded as a synonym of E. rutili. The Octosporella species described from fish are based on erroneous identification and should be considered nomina nuda. Similarly, the Eimeria and Isospora species described from fish by Davronov in 1987 should also be regarded as nomina nuda, as they appear to be avian or mammalian coccidia that entered the intestinal tract of fish with food. The sporocyst residua of fish coccidia cannot be used as characters suitable for species identification, as they tend to change with oocyst aging.