Theses and Dissertations

Issuing Body

Mississippi State University


Griffin, Matthew J.

Committee Member

Wise, David

Committee Member

Khoo, Lester H.

Committee Member

Greenway, Terrence E.

Date of Degree


Document Type

Dissertation - Open Access


Veterinary Medical Science

Degree Name

Doctor of Philosophy


College of Veterinary Medicine


Veterinary Medical Science Program


Myxozoans are cnidarian parasites of primarily freshwater and marine fish, with some being important pathogens of aquacultured fish species worldwide. Their life cycles have waterborne actinospores released from aquatic annelid definitive hosts and myxospore stages in fish intermediate hosts. In the southeastern United States, catfish aquaculture is burdened by annual losses to a myriad of infectious diseases. Henneguya ictaluri, the causative agent of proliferative gill disease in channel catfish Ictalurus punctatus and female channel catfish x male blue catfish Ictalurus furcatus hybrids, is the most commonly diagnosed parasitic disease of catfish in Mississippi. Other myxozoans infect these ictalurid fish, but their impact on catfish production is unknown. Surveys of actinospores from the oligochaete Dero digitata and myxospore stages from fish revealed an unexpected diversity for these production systems. Six genetically distinct actinospores representing four collective groups were observed from D. digitata. Herein, two novel Henneguya spp. are described from the gills and a novel Unicauda sp. is described from the intestinal tract of channel catfish. One Henneguya sp. was linked to its actinospore stage and represents the fourth known life-cycle in the genus. In addition to catfish, smallmouth buffalo Ictiobus bubalus polycultured with catfish were examined and two Myxobolus spp. were characterized from the gills. Phylogenetic analyses strongly support a clade of ictalurid Henneguya spp. and a clade of catostomid Myxobolus spp. Although diverse, H. ictaluri is the only myxozoan in catfish attributed to significant losses. With no feasible method of control or treatment, investigations into less susceptible fish were initiated and showed promise. Infectivity trials characterizing H. ictaluri development in channel, blue, and hybrid catfish were performed. Channel catfish were suitable hosts with myxospores developing in the gills by six weeks and persisting for at least 14 weeks. In hybrid catfish arrested or limited development was observed with no pseudocysts observed during Trial 1 and only two at 14 weeks during Trial 2. These results may suggest a possible way of decreasing losses attributed to PGD through hybrid catfish monoculture or fish crop rotation to reduce the number of infectious myxospores released into the pond.