Activation ofHenneguya ictaluriActinospores by Nonictalurid Fish Species, with Implications for Management of Proliferative Gill Disease in Catfish Aquaculture

Abstract

AbstractProliferative gill disease (PGD), caused by the myxozoanHenneguya ictaluri, is an important parasitic disease in U.S. catfish aquaculture. Continuous exposure of Channel CatfishIctalurus punctatusto the actinospore stage ofH.ictaluriresults in a severe inflammatory response at the gills, leading to morbidity and death. Previous work indicates that the chemical cues in fish mucus that are recognized by myxozoan actinospores are not host specific. Building on these findings, the potential decoy effects of nonictalurid fish to actinospores ofH.ictaluriwere evaluated. Exposure of actinospores to gill mucus from multiple nonictalurid fishes resulted in actinospore activation for all fish species tested. Based on these findings, experimental transmission trials with potential interceptor fish were conducted. Individual Channel Catfish were co‐stocked with Western MosquitofishGambusia affinisat 0, 10, 25, or 50% of mean Channel Catfish biomass and exposed to 3,000 actinospores ofH.ictaluri. Gill tissues were sampled at 24 h postchallenge, and parasite burden was estimated byH.ictaluri‐specific quantitative PCR. Results revealed that Western Mosquitofish stocked at 25% and 50% of catfish biomass reducedH.ictaluriDNA in Channel Catfish gills more than threefold. In a second study, catfish were exposed to pond water collected from an active PGD outbreak in the presence of Western Mosquitofish stocked at 25% of catfish biomass. Channel Catfish were sampled at 24 h and at 7 d after the last pond water exposure. At 24 h postexposure, catfish that were co‐stocked with Western Mosquitofish showed significantly lowerH.ictaluriDNA than catfish stocked alone. This treatment effect was absent at 7 d postexposure, as parasite quantities within tissues had increased over 1,000×, with marked variability. Still, results indicate that the chemical cues that activateH.ictaluriactinospores are not specific to Channel Catfish. This work evinces a potential benefit of nonictalurid fish in combatingH.ictaluri, suggesting that the presence of nonictalurid interceptor fish in catfish ponds may minimize PGD severity.