New trends in parasitic infections of cultured freshwater fish

The 1980s are characterized by the appearance of new fish parasitoses, the clarification of the aetiology of diseases and new insights into the process of infection and the development of important parasites, especially myxosporidians. Two phaerosporoses have entered into the foreground: swimbladder inflammation (SBI) caused by Sphaerospora renicola in common carp and proliferative kidney disease (PKD) in salmonids. Both diseases must be reported in the German Democratic Republic (GDR). The connection between the "C-protozoa" in the blood and S. renicola in SBI was recently clarified by experiments by Molnar (1988). The results of our own investigations indicate that the "K-protozoa" phase of S. renicola parasitizes mainly the brain and sometimes the spleen, pancreas and liver before appearing in the swimbladder. Hedrick et al. (1988) in the USA and Odening et al. (1988b) in Europe first reported a Sphaerospora sp. in Salmo gairdneri in connection with PKD. The spectacular findings by Wolf and Markiw (1984) and El-Matbouli (1988) elucidating on the life cycle of Myxobolus cerebralis have not yet brought the revolutionary change expected for a general new estimation of myxosporidian transmission as a basis for ecotechnological control measures. Examples for the formation of new regionally specific parasite colonizations offer the far Eastern cyprinids introduced into Europe. In the GDR the silver carp is infected by Chloromyxum barbi (Myxosporidia) (Sedlazsek), the pathogenic Gyrodactylus sprostonae and two new Gyrodactylus species (Pectobathrii) (Lux). Eel parasites new to Europe are the obviously imported and highly pathogenic nematodes Anguillicola crassus and A. novaezelandiae (Paggi et al., 1982; Moravec and Taraschewski, 1988). In Central Europe the infestation of rainbow trout by the tapeworm Proteocephalus neglectus is increasing (Priemer, 1980; Hanzelova et al., 1988).