Experimental studies on the intraoligochaete development of myxosporean fish parasites

From the authors' own experiments as well as from data of the literature it now seems unquestionable that myxosporeans, which are common pathogens of fish, are primitive metazoan parasites that develop via alternate hosts (a fish and an oligochaete species). In laboratory experiments with 7 myxospor ean species, the authors infected oligochaetes with myxospores collected fr om fish and demonstrated the emergence of actinospores after a development period of 2-5 months. In the case of the species Myxobolus drjagini, M. por tucalensis and M. hungaricus the development in Tubifex tubifex resulted in triactinomyxon-type actinospores, while the species Al. dispar gave rise t o raabeia-type actinospores as a result of development in the same alternat e hosts. The development of two Thelohanellus species and Sphaerospora reni cola took place in the oligochaete Branchiura sowerbyi, T. nikolskii and T. hovorkai formed aurantiactinomyxon-type while S. renicola gave rise to neo actinomyxon-type spores. Comparing our own results with data of the literat ure it appears that the Myxobolus species best known from fish appear in tr iactinomyxon or raabeia forms in their alternate hosts, whereas sphaerospor es and the species taxonomically close to them form neoactinomyxon spores. The aurantiactinomyxon-type spores seem to represent the commonest form, si nce this is the spore form in which the actinospore stages of even taxonomi cally distant myxosporeans may appear.