Location: Warmwater Aquaculture Research UnitTitle: Application of A Real-Time PCR Assay for The Detection of Henneguya ictaluri In Commercial Channel Catfish Ponds Author
Submitted to: Diseases of Aquatic Organisms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/20/2009
Publication Date: 11/9/2009
Citation: Griffin, M.J., Pote, L.M., Camus, A.C., Mauel, M.J., Greenway, T.E., Wise, D.J. 2009. Application of A Real-Time PCR Assay for The Detection of Henneguya ictaluri In Commercial Channel Catfish Ponds. Diseases of Aquatic Organisms. 86:223-233. Interpretive Summary: Proliferative gill disease (PGD) in channel catfish Ictalurus punctatus is caused by the myxozoan parasite Henneguya ictaluri. Prolonged exposure of channel catfish to the parasite results in extensive gill damage, leading to reduced production and significant mortality in commercial operations. Currently there are no effective treatments for PGD, but we have shown that moving fish to water free of the parasite results in rapid recovery. To help assess which ponds do not contain the parasite we developed a molecular based test that can determine how many parasites are in pond water. This test is being used by the Aquatic Research & Diagnostic Laboratory as a diagnostic tool to evaluate parasite levels in pond water and determine when fish can be safely stocked in ponds.
Technical Abstract: Proliferative gill disease (PGD) in channel catfish Ictalurus punctatus is caused by the myxozoan parasite Henneguya ictaluri. Prolonged exposure of channel catfish to the actinospore stage of the parasite results in extensive gill damage, leading to reduced production and significant mortality in commercial operations. A H. ictaluri-specific real-time (Q) PCR assay was used to determine parasite levels in commercial channel catfish ponds and evaluate the risk of losing fish newly stocked into the system. Previous research has shown the H. ictaluri actinospore to be infective for approximately 24 h; therefore, determining the parasite load (ratio of parasite DNA to host DNA) in sentinel fish exposed for 2 separate 24 h periods with a minimum of 1 wk between sampling indirectly represents the rate at which infective actinospores are being released by the oligochaete host and if that rate is changing over time. Alternatively, QPCR analysis of pond water samples eliminates the need for sentinel fish. Water samples collected on 2 separate days, with a minimum of 1 wk between sampling, not only determines the approximate concentrations of actinospores in the pond but if these concentrations are remaining stable. Increases in parasite load (r = 0.69, p = 0.054) correlated with percent mortality in sentinel fish, as did increases in mean actinospore concentrations (r = 0.63, p = 0.003). Both applications are more rapid than current protocols for evaluating the PGD status of a catfish pond and identified actinospore levels that correlate to both high and low risk of fish loss.