Coussens

The elucidation of the life cycle of a Hysteromorpha sp. in ictalurid catfish production systems in Mississippi, USA

Caroline D. Coussens1, Ethan T. Woodyard2, MacKenzie A. Gunn3, D. Tommy King4, Bradley Richardson3, Lauren Easter1, Jonah Nguyen1, David J. Wise3,5, Matt J. Griffin2,6 and T. Graham Rosser1

1Department of Basic Sciences, College of Veterinary Medicine, Mississippi State University, Mississippi State, MS; 2Department of Pathobiology and Population Medicine, College of Veterinary Medicine, Mississippi State, MS; 3Department of Wildlife, Fisheries and Aquaculture, College of Forest Resources, Mississippi State University, Mississippi State, MS; 4National Wildlife Research Center, USDA-APHIS, Starkville, MS; 5Mississippi Agriculture and Forestry Experiment Station, Thad Cochran National Warmwater Aquaculture Center (NWAC), Delta Research and Extension Center (DREC), Stoneville, MS; 6Aquatic Research and Diagnostic Laboratory, NWAC, DREC, Stoneville, MS

ABSTRACT

Ictalurid catfish production is the largest aquaculture industry in the United States, with over half of production localized in Mississippi. Two major challenges facing the industry are the consumption of fish and the introduction of trematode parasites by piscivorous birds. Management of trematode infections is dependent on identifying all hosts in the life cycle, as there are no approved antiparasitic medications. In Summer 2019, the MSU Aquatic Parasitology Lab observed reduced feeding activity in catfish infected with a Hysteromorpha species. The purpose of this project was to determine the life cycle of Hysteromorpha sp. in Mississippi, so that catfish producers could develop management strategies targeting the snail host. Double crested cormorant (n=26) small intestines were screened for adult Hysteromorpha, while fish from the original Hysteromorpha outbreak were necropsied to recover metacercaria. Snails collected from catfish ponds were screened for the shedding of cercaria. Each life stage was morphologically and molecularly characterized by sequencing mitochondrial and ribosomal gene regions for species identification and life cycle elucidation. Channel catfish fingerlings were challenged with cercaria recovered from shedding snails. Evaluation of mitochondrial cytochrome c oxidase subunit 1 data identified our specimens as Hysteromorpha corti. Sequence data indicated conspecificity of all life stages and implicated Planorbella trivolvis as the snail host for H. corti. Molecular analysis revealed the cercariae used in catfish challenges as a separate diplostomid species and future research will focus on identifying these, as well as investigating pathogenicity of H. corti.

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