Stocking Larger Fingerlings Does Not Reduce Risk To Proliferative Gill Disease

Authors: Richardson, Bradley; UL-HUDA, NOOR - Mississippi State University; CAMUS, ALVIN - University Of Georgia; WALKER, CHARLES - Mississippi State University; Older, Caitlin; YAMAMOTO, FERNANDO - Mississippi State University; STILWELL, JUYSTIN - Mississippi State University; WARE, CYNTHIA - Mississippi State University; MARANCIK, DAVID - St George'S University; WISE, DAVID - Mississippi State University; GRIFFIN, MATT - Mississippi State University

Submitted to: Thad Cochran NWAC News
Publication Type: Trade Journal
Publication Acceptance Date: 8/29/2024
Publication Date: 12/1/2024
Citation: Richardson, B.M., Ul-Huda, N., Camus, A.C., Walker, C.M., Older, C.E., Yamamoto, F.Y., Stilwell, J.M., Ware, C., Marancik, D.P., Wise, D.J., Griffin, M.J. 2024. Stocking Larger Fingerlings Does Not Reduce Risk To Proliferative Gill Disease. Thad Cochran NWAC News. https://www.tcnwac.msstate.edu/docs/NWAC_2024.pd.

Interpretive Summary: Proliferative gill disease (PGD) is the most common parasitic disease diagnosed at the Aquatic Research and Diagnostic Laboratory (ARDL) at the Thad Cochran National Warmwater Aquaculture Center (NWAC) in Stoneville, Mississippi. Colloquially known as “Hamburger Gill”, the disease is caused by the myxozoan parasite Henneguya ictaluri. In response to stakeholder inquiries, NWAC scientists in collaboration with researchers at Mississippi State University College of Veterinary Medicine, St. George’s University, and the University of Georgia, conducted a field study using sentinel channel catfish fingerlings to assess variation in PGD severity in different sized fish stocked into the same ponds. Fingerling catfish representing two industry-relevant size-classes (40 lbs/1000 [small] and 120 lbs/1000 [large]) were placed into net pens and distributed across ponds with varying levels of H. ictaluri concentrations in the water. Survival was similar between both size-classes. While the mortality curve was steeper for smaller fish, overall mortality was comparable and there was no observed benefit to stocking larger fingerlings in terms of PGD-related mortalities (Fig. 1). Fish size also had no effect on any sublethal gill pathology. Parasite burden was the best predictor of gill damage and disease severity. Thus, the results of the study show significant protection against PGD based on fish size. Stocking size should be based on production goals and strategies of individual farms rather than as an attempt to mitigate PGD-related losses. This research supports the Secretary of Agriculture's priority to increase productivity and profitability of farmers.

Technical Abstract: Proliferative gill disease (PGD) is the most common parasitic disease diagnosed at the Aquatic Research and Diagnostic Laboratory (ARDL) at the Thad Cochran National Warmwater Aquaculture Center (NWAC) in Stoneville, Mississippi. Colloquially known as “Hamburger Gill”, the disease is caused by the myxozoan parasite Henneguya ictaluri. In response to stakeholder inquiries, NWAC scientists in collaboration with researchers at Mississippi State University College of Veterinary Medicine, St. George’s University, and the University of Georgia, conducted a field study using sentinel channel catfish fingerlings to assess variation in PGD severity in different sized fish stocked into the same ponds. Fingerling catfish representing two industry-relevant size-classes (40 lbs/1000 [small] and 120 lbs/1000 [large]) were placed into net pens and distributed across ponds with varying levels of H. ictaluri concentrations in the water. Survival was similar between both size-classes. While the mortality curve was steeper for smaller fish, overall mortality was comparable and there was no observed benefit to stocking larger fingerlings in terms of PGD-related mortalities (Fig. 1). Fish size also had no effect on any sublethal gill pathology. Parasite burden was the best predictor of gill damage and disease severity. Thus, the results of the study show significant protection against PGD based on fish size. Stocking size should be based on production goals and strategies of individual farms rather than as an attempt to mitigate PGD-related losses.