New results in the research of fish parasitic myxosporeans.: Literature review and own experiences

Research on myxosporeans is one of the most dynamically developing fields of fish parasitology. The results achieved in recent years prompted the author to write an overview, which is a continuation of relating papers published in this journal earlier, including a review in 1999 on the life cycles of myxosporeans, and another paper on molecular studies in 2002. In recent years, the Hungarian fish pathological research group achieved results in the following fields: (1) New myxosporean species have been described in Hungary, such as Myxobolus margitae from the gills of bleak and M. intrachondrealis from the cartilage of the gill arches of one- and two-summer-old common carp. (2) In addition to the new species, several myxosporean species previously recorded only in other parts of the world were detected in Hungary for the first time, such as M. diversus Nie et Li, 1973, a parasite of the fins of goldfish or M. cyprinkola Reuss, 1906 infecting the gut of common carp. (3) Recently, actinosporean stages of three Myxobolus species (M. bramae, M. pseudodispar and M. macrocapsulari) have been detected from their experimentally infected oligochaete alternate hosts. Triactinomyxon-type actinospores were detected in each case. (4) In the case of the species M. pseudodispar, the complete developmental cycle could be reproduced, i.e. laboratory-cultured SPF fish were successfully infected with experimentally obtained actinospores. (5) In addition to studying the actinosporean infection of oligochaetes collected from Hungarian fish farms and natural waters, actinospores have been detected from oligochaetes collected in Japanese, Spanish and Estonian biotopes, in many cases for the first time in the given country. (6) The importance of localisation within the fish host and tissue specificity, as a phenotypic characteristic important in addition to spore morphology, has been highlighted in connection with the development of some myxosporeans infecting the fins of fish in Hungary. (7) in the framework of molecular studies on myxosporeans, studies on the structure of 18S rRNA gene of some Myxobolus spp. infecting the muscles of fish proved that the new parasite species had developed through parallel evolution with the fish hosts.