Etiological and Epizootological Factors Associated with Outbreaks of Proliferative Gill Disease in Channel Catfish

Abstract

Water, sediment, and channel catfish Ictalurus punctatus were sampled from seven farms experiencing proliferative gill disease (PGD) outbreaks in spring 1992. At each farm, samples were collected from the pond that experienced the outbreak (PGD-positive pond) and from another pond where no PGD was observed (control pond). Seven species of Actinosporea were detected in the oligochaete populations of the ponds examined The only actinosporean species significantly (P ≤ 0.05) correlated with clinical PGD outbreaks was Aurantiactinomyxon sp. (type 1). Population densities of aquatic oligochaetes in the pond sediments, including Dero digitata, the host of Aurantiactinomyxon sp., were surveyed during the PGD outbreaks and over the following year. Population densities of all oligochaetes, densities of D. digitata, and proportions of the total oligochaete population represented by D. digitata were all significantly higher (P ≤ 0.05) in ponds experiencing clinical outbreaks of PGD than in control ponds. After the PGD outbreaks, total oligochaete density returned to levels not significantly different from those of control ponds. During the study, PGD organisms were observed in fish from control ponds, and the prevalence of Aurantiactinomyxon sp. (type 1) infection of D. digitata was similar to that in the PGD-positive ponds. However, the control ponds with PGD-positive fish had lower densities of D. digitata. Water analysis showed that PGD-positive ponds had significantly (P ≤ 0.05) lower turbidity than control ponds. Organic content of soil in positive and control ponds did not significantly (P ≤ 0.05) differ.