ABSTRACT
Aims: To ascertain the gastrointestinal nematode burden on the channids, Parachanna obscura and Parachanna africana (Steindachner, 1879) (Family: Channidae) in the down reaches of Orogodo River at Evboesi and Ekwuoma-Abavo, southern Nigeria and its relationship to the levels of organic pollution. Study Design: A total of 220 channid fish were collected from two stations of the river experiencing different degree of organic pollution and dissected for gastrointestinal nematode parasites Place and Duration of Study: The study lasted for a period of six months (Jan to Jun 2010) with collections of fishes done monthly at two sampling stations of Orogodo River in southern Nigeria. Methodology: A total of 220 channid fishes were examined. Their stomachs and intestines were cut open and the contents were emptied into Petri dishes containing water and were examined for nematode parasites. These were quickly stained with Giemsa stain and viewed under a light microscope. Results: A total of 100 (45.5%) were infected with gastrointestinal nematode parasites. The prevalence of infection reveals that Parachanna obscura recorded 62.5% while Parachanna africana had 66.7% in fishes collected from station 1 and 20.1% and 28.6% respectively from fishes collected at station 2. The nematode parasites recovered were Cucullamus sp., Camallanus sp. and Procamallanus laevionchus. The overall parasitic burden reveals that the prevalence infection was statistically significant (p< 0.05) in the species examined. The distribution of infrapopulations of the parasites varied significantly with size class and weight of the fish peaking in most cases in larger size classes. The chemical parameters of the river water at station 1 showed the water to be stressed with high BOD and nutrients levels when compared with station 2. This may explain the high parasitic burden recorded in the channids at station 1. Conclusion: The intensity of the parasites in the host fish agree with previous hypotheses suggesting that environmental pollution does affect parasite population.