Endo-parasitic helminthes of four mormyrid species (Osteichthyes: Mormyridae) from a West African flood river system

Mormyrus rume rume, Hyperopisus bebe bebe, Campylomormyrus tamandua and Gnathonemus petersii sampled from the Anambra river with a fleet of gill nets, traps and hook and line were examined for endo-parasitic helminthes from October 2005 to September 2006. Recovered helminthes were Rhadinorhynchus horridus from the intestine of H. bebe bebe and G. petersii; Procamallanus laeviconchus from the stomach of M. rume rume and C. tamandua; Spinitectus mormyri from the stomach of M. rume rume; Contracaecum sp. from the coelom of H. bebe bebe, G. petersii and C. tamandua, whereas an unidentified cestode infected the intestine of all the mormyrids. G. petersii constitutes a new host record for R. horridus; M. rume rume for S. mormyri and M. rume rume and C. tamandua for P. laeviconchus. In cases of mixed infection the parasites occupied their preferred habitats. The overall prevalence of the endo-parasites in the fish hosts was 41.9%, which is within the range (< 50%) typical of southern Nigerian freshwater lotic habitats. Prevalence, mean intensity and mean abundance of R. horridus in its host fishes were higher in the dry (October/November-March) than the rainy season (April-September/October); in the nematodes (P. laeviconchus, S. mormyri and Contracaecum) the reverse was the case, whereas no definite pattern was exhibited by the unidentified cestode. P. laeviconchus appeared reddish from engorgement of blood but no damage was evident at the point of attachment. Local inflammation where R. horridus was attached to the mucosa of the intestine was not considered severe. R. horridus and P. laeviconchus are probably the most important parasites of the mormyrids in terms of fishery management in the Anambra river system.