Effects of a thermal effluent on the incidence and abundance of the gill and intestinal metazoan parasites of the black bullhead

Abstract

SUMMARYEffects of thermal effluent on the incidence and abundance of gill and intestinal metazoan parasites of the black bullhead, Ictalurus melas, were investigated. A total of 472 bullheads from a thermal outfall area and an unaltered area of Lake Monona, Dane County, Wisconsin were examined. All parasites underwent a seasonal cycle in abundance with peak infections occurring in summer, except for the acanthocephalan, Pomphorhynchus bulbocolli, which underwent a seasonal cycle in abundance in the reference area but not in the outfall area. Thermal effluent had little effect on the incidence of the parasites. Differences in abundance between the outfall and reference areas were observed for all parasites but these differences were not always consistent nor statistically significant. P. bulbocolli was more abundant in the reference area than in the outfall area in summer (P ≤ 0·05). The monogenean, Cleidodiscus sp. was more abundant in the reference area than in the outfall area in August (P ≤ 0·05). The infections of the gill copepod, Achtheres ambloplitis, were higher in the reference area than in the outfall area in spring, June, August, and September (P ≤ 0·05). Availability of infective larvae and variability in host feeding patterns were suggested as the controlling factors of the patterns of abundance observed.