Abstract
Since the epoch-making discovery of the life-cycle of Myxobolus cerebralis by Wolf and Markiw (1984), studies on myxozoan parasites of fishes have continued to progress rapidly. Molecular analyses of myxozoan SSUrDNA have been successful in clarifying its systematic position not as protozoans but as metazoans. However, there remain gaps in our understanding of their biology and pathology. Alternate myxosporean and actinosporean stages in the life-cycles of more than 25 species of freshwater myxozoan have been demonstrated, but many unresolved questions remain, e.g., the relationship between the parasite and its alternate invertebrate hosts and the mode of transmission in marine myxozoans. These unsolved questions have made it difficult to design an effective control strategy for myxozoan diseases. Recent studies on countermeasures have been directed towards the introduction of resistant fish strains and controlling oligochaete populations.
