The role of copepods (Cyclops spp.) in eliminating the actinospore stages of fish-parasitic myxozoans.

The actinospore consumption of copepods (Cyclops spp.) was demonstrated by laboratory observations. It was observed that in experimental dishes the number of actinospores floating in the water decreased, or such actinospores were completely eliminated, in the presence of copepods. The ingestion of actinospores by copepods and their further fate were monitored by fluorescent staining and by conventional histological techniques. The actinospores were observed to have got caught on the filters of Cyclops spp. Two and a half hours after the copepods had been placed into water containing actinospores, their digestive tract was found to contain spores that had extruded their filaments from the polar capsules. After copepods having ingested the actinospores of the species Myxobolus pseudodispar had been fed to roaches, no muscle infection developed in the fish host. It is likely that Cyclops spp. can filter out actinospores floating in the water also from natural waters, thus decreasing the chance of development of myxosporean infections.