Myxozoa parasites of oligochaetes in river basins with intensive troutfarming activities

摘要

The aim of this study was to check the occurrence of Myxozoan actinospores parasitizing oligochaetes in the Nera River basin (Umbria, central Italy), where several intensive trout farms (rainbow and brown trout) are present. Specimens of oligochaetes were collected during April 2005 from twenty-four sampling stations, located upstream and downstream twelve facilities on the Nera River and its tributaries: Campiano, Sordo, Corno and Vigi rivers. Collected oligochaetes were cultured in cell-well plates, according to Yokoyama H et al. The spore type was assigned to a collective group following the keys of Janisewska J and measured according to the guidelines of Lom J et al. A single actinosporean type, belonging to the collective group echinactinomyxon, was detected in the Sordo River (upstream and downstream two trout farms) and in the Campiano River (upstream and downstream a single trout farm). In these sites, where only trout hatcheries are present, no fish infection due to Myxozoa was detected. Infected specimens of oligochaetes were immature Lumbriculidae, probably Lumbriculus variegatus (Mueller), the only identified species among adult Lumbriculidae. The greatest infection incidence was detected in the Sordo River, where the estimated mean percentage of infection was 14.75% on 254 Lumbriculidae specimens. The examined spores showed at least four branches at the end of the caudal processes. This feature, together with the spore dimensions and the number of secondary cells (i.e. about 16), makes this echinactinomyxon type comparable to the echinactinomyxon type described by Szekely CS et al from Rhyacodrilus komarovi Timm. Further investigations will be necessary to identify the myxozoan species and to understand their life cycle stages.