Occurrence of myxosporean parasites in the gills of two tilapia species from Lake Nokoué (Bénin, West Africa): effect of host size and sex, and seasonal patterns of infection.

The gill myxosporean parasites of 2 euryhaline tilapias from Lake Nokoué, Sarotherodon melanotheron melanotheron (Rüppel, 1853) and Tilapia zillii (Gervais, 1852), were investigated from October 1987 to October 1989. A total of 391 S. m. melanotheron and 222 T. zillii were examined. Both of the fish species studied were infected by 3 host-specific myxosporean parasites for which prevalence greatly varied during our investigations. The 2 most common ones were Myxobolus sp. and M. zillii, which were located in the branchial filament. No significant fish sex effect was found for these 6 different myxosporean parasites. As seasonal pattern was clearly demonstrated for M. zillii while a host size effect was found for M. dossoui. However, further investigations of these myxosporean infections are necessary to determine the real effect of these parasites on their host, as host fecundity and survival was not assessed.