Influence of channel catfish (Ictalurus punctatus) and channel x blue catfish (I. furcatus) hybrids on myxozoan community composition in catfish aquaculture ponds

Authors: STILWELL, JUSTIN - University Of Georgia; CAMUS, ALVIN - University Of Georgia; WARE, CYNDI - Mississippi State University; WALKER, CHARLES - Mississippi State University; STANTON, JAMES - University Of Georgia; LEARY, JOHN - University Of Georgia; KHOO, LESTER - Mississippi State University; WISE, DAVID - Mississippi State University; Waldbieser, Geoffrey - Geoff; GRIFFIN, MATTHEW - Mississippi State University

Submitted to: North American Journal of Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/18/2023
Publication Date: 6/26/2023
Citation: Stilwell, J., Camus, A., Ware, C., Walker, C., Stanton, J., Leary, J., Khoo, L., Wise, D., Waldbieser, G.C., Griffin, M. 2023. Influence of channel catfish (Ictalurus punctatus) and channel x blue catfish (I. furcatus) hybrids on myxozoan community composition in catfish aquaculture ponds. North American Journal of Aquaculture. 85:242-251. https://doi.org/10.1002/naaq.10293.
DOI: https://doi.org/10.1002/naaq.10293

Interpretive Summary: Proliferative gill disease in catfish, caused by the myxozoan parasite Henneguya ictaluri, leads to millions of dollars of production losses to producers due to fish morbidity and mortality. Prior research has shown that channel x blue catfish hybrids experience lower levels of this disease than do channel catfish. Researchers at the USDA, ARS, Warmwater Aquaculture Research Unit in Stoneville, MS, cooperated with researchers at Mississippi State University and the University of Georgia to examine the composition of Henneguya species present in infected ponds. Using a molecular genetic technology called metagenomics, the group quantified DNA sequences from Henneguya species that were present in pond water samples collected over three years. The results showed lower levels of Henneguya ictaluri in ponds that contained hybrid catfish compared to ponds containing only channel catfish, and the experiments identified many more myxozoan species related to Henneguya ictaluri in these ponds. The research provided more evidence to suggest that rotating production cycles of channel catfish and hybrid catfsih in ponds could disrupt the life cycle of pathogenic myxozoans and reduce the incidence of proliferative gill disease.

Technical Abstract: The myxozoan Henneguya ictaluri is cited as the cause of proliferative gill disease in channel catfish (Ictalurus punctatus) and channel × blue catfish (Ictalurus furcatus) hybrids. Differences in host susceptibility results in decreased transmission rates, reduced sporogenesis and lesser incidence of PGD in hybrid catfish. In experimental pond trials, continuous monoculture of hybrid catfish suppressed H. ictaluri abundance in pond systems compared to channel catfish. The present study examined differences in myxozoan community structure in catfish ponds stocked with channel or hybrid catfish. Experimental ponds (0.4 ha) dedicated to channel or hybrid catfish monoculture were maintained over three production cycles. Pond water collected during the spring of each year was subjected to metagenomic analysis by targeted amplicon sequencing of a diagnostic hypervariable region (DVR3) of the myxozoan 18S rRNA gene. In channel catfish ponds, H. ictaluri relative abundance was significantly greater compared to hybrid ponds in Years 2 and 3. In hybrid catfish ponds, H. ictaluri never exceeded 20% average relative abundance. Hybrid catfish ponds also revealed decreased myxozoan diversity and species evenness compared to channel catfish ponds, suggesting myxozoan taxa associated with channel catfish may not be well adapted to the hybridized host. Results corroborate previous research indicating hybrid catfish monoculture can suppress H. ictaluri compared to ponds devoted to channel catfish. These data imply alternating catfish culture species in ponds (crop rotation) has potential to mitigate PGD by precluding H. ictaluri from accumulating within ponds to levels associated with disease and catastrophic loss. Further, this work identified numerous previously unidentified taxa present within these systems that cluster phylogenetically with both catfish and non-catfish hosts. The impacts these other myxozoans have on catfish health and production is unknown but indicates myxozoan diversity within catfish aquaculture ponds has been greatly underestimated and is significantly influenced by stocking choice.