The Effects of Proliferative Gill Disease on the Blood Physiology of Channel Catfish, Blue Catfish, and Channel Catfish × Blue Catfish Hybrid Fingerlings

Abstract This study was conducted to gain a better understanding of the effect of exposure to the myxozoan Henneguya ictaluri (the agent of proliferative gill disease [PGD]) on host physiology by measuring the variation in selected blood characteristics in three differently affected host taxa (channel catfish Ictalurus punctatus, blue catfish I. furcatus, and blue catfish × channel catfish hybrid fingerlings). Forty-five fish of each host taxon were exposed to PGD, and 10 fish of each host taxon were sampled at 24, 96, and 168 h. Fish were weighed, blood was collected and analyzed for a suite of physiological variables, and wet mount preparations of gill clips were examined grossly for the presence of cartilage breaks. The results of this study are consistent with the current knowledge regarding H. ictaluri infections in blue catfish, channel catfish, and blue catfish × channel catfish hybrids. Chondrocytic lysis was observed in channel catfish and hybrid catfish at 96 and 168 h but was not observed in blue catfish. There was an observed reduction in oxygen partial pressure (pO2) and an increase in carbon dioxide partial pressure (pCO2) at 96 h in the blood of channel catfish and hybrid catfish, but these changes were not exhibited by blue catfish. For all species, pH decreased as lactate concentrations increased. The lack of physiological changes and the absence of H. ictaluri sporozoites and DNA in gill tissue lead us to speculate that H. ictaluri is unable to establish infection in blue catfish. Current research investigating the mechanisms of infection and portals of parasite entry into blue catfish, channel catfish, and blue catfish × channel catfish hybrids is underway to better elucidate the defenses employed by blue catfish against H. ictaluri.