Small Subunit Ribosomal RNA Sequences Link the Cause of Proliferative Gill Disease in Channel Catfish to<i>Henneguya</i>n. sp. (Myxozoa: Myxosporea)

Abstract

In a previous study the small subunit ribosomal RNA (SSU rRNA) gene of Aurantiactinomyxon ictaluri, the actinosporean stage (actinospore) of the myxozoan associated with proliferative gill disease (PGD), was sequenced. In this study bath exposures of channel catfish Ictalurus punctatus to A. ictaluri isolated from the aquatic oligochaete Dero digitata were used to study the subsequent development of this parasite and to confirm the SSU rRNA gene sequences of each life stage. On day 7 postexposure, typical PGD organisms were observed in the gills, and at 3 months postinfection, cysts containing the newly identified myxozoan Henneguya sp. spores were observed in the gills. The sequence of the SSU rRNA genes of the actinospore and myxospore life stages demonstrated their identity. This is the first molecular evidence that A. ictaluri, isolated from D. digitata, can infect catfish and produce the typical PGD organisms in the gills. These data provide further proof that the actinospore A. ictaluri is actually a life stage of the myxospore H. ictaluri n. sp. described in this paper. Further studies are needed to confirm that H. ictaluri n. sp. spores can infect D. digitata, thus completing the life cycle of this parasite.