In Search of the Cause of Proliferative Gill Disease in Channel Catfish,Ictalurus punctatus:

Abstract

A two-year study was conducted on three ponds at a commercial channel catfish, Ictalurus punctatus, farm that experienced severe losses of channel catfish to proliferative gill disease (PGD) during the winter of 1988/1989. Low levels of mild PGD persisted throughout the year. Outbreaks of PGD with resulting mortalities occurred in both hot and cool months. Mortalities associated with PGD occurred in Pond 37 in its first vear of production and in Pond 42 in both its fist and second years of production; Pond 42 had been drained and dried following a PGD outbreak in the spring of its first year. PGD-related mortalities did not occur in Pond 21 in either its third or fourth years of continual production, despite the presence of histologically detectable PGD in the third year. Hennegiya exilis and Sphaerospora were only occasionally observed in PGD-affected channel catfish. Seasonal changes in PGD prevalence were correlated with changes in myxozoan infection of small mud-dwelling worms, Dero digitata (Oligochaeta: Naididae). The myxozoan is an undescribed species of Aurantiactinomyxon (Actinomyxea: Triactinomyxidae). D. digitata and isolated spores of Aurantiactinomyxon sp. were the only pond organisms that produced PGD in laboratory experiments. Comparison of the oligochaete populations of the study ponds suggested that differences in PGD prevalence in channel catfish raised in "old" and "new" ponds may be related to oligochaete population diversity. Channel catfish naturally infected with PGD recovered completely when held in tanks supplied with well water.