Protozoan parasites of fish

Abstract

Studies have been carried out on protozoan parasites of freshwater fish from the Amazon region of Brazil, and the British Isles. Special emphasis has been given to aspects of the taxonomy and life - history of species of the order Myxosporida. In section 1, full descriptions are given of Myxosporida from Brazilian and British fish. The Brazilian species include three of the genus Myxobolus from piranha (Serrasalmus sp, and S. rhombeus) and tambaqui (Colossoma bidens), and Agarella gracilis from lungfish (Lepidosiren paradoxa). In British fish, Myxobolus species are described from roach (Rutilus rutilus), gudgeon (Gobio gobio) and dace (Leuciscus leuciscus); Myxidium species are described from roach, gudgeon and salmon (Salmo salar). The similarity of the genera Myxobolus and Myxosoma is noted, and the difficulty of distinguishing them is pointed out. From the result of histochemical tests for glycogen In spores of selected species, it is proposed that the two genera should be synonymised as Myxobolus. Accounts are given of attempts to establish infections of Myxidium in Myxidium - free roach and salmon. The negative results of these experiments suggests that myxosporidan spores may need to undergo some form of further development outside the host before becoming infective to a new host. Check - lists are given of species of Myxobolus, Myxidium and, recently described Myxosoma species. In section 2, other protozoa, including two species of Microsporida, one coccidian species, and Rhabdospora thelohani are described and discussed.