Infection patterns of Myxobolus heterospora in two tilapia species (Teleostei: Cichlidae) and its potential effects.

A Myxobolus heterospora (Baker, 1963) infection was found in 2 euryhaline tilapia species, Sarotherodon melanotheron melanotheron (Rüppel, 1853) and Tilapia zillii (Gervais, 1852), from a brackish water lake, Lake Nokoué (Benin, West Africa). The histology and ultrastructure of different levels of infection in intestinal connective tissues and wall tissues is described. A total of 391 S. melanotheron melanotheron and 222 T. zillii were examined from October 1987 to October 1989. M. heterospora was found throughout the study period, with a total prevalence of 42.19 and 26.57% for S. melanotheron melanotheron and T. zillii respectively. There was a statistically significant difference in occurrence as a function of season in S. melanotheron melanotheron but not in T. zilli, and there was a significant difference for size and sex in the former and for sex in the latter. M. heterospora induces total destruction of the intestine structure and probably leads to osmoregulatory disturbance. Further investigations of this myxosporean infection are necessary to determine its real effect on the host, since host survival and osmoregulatory rate have not yet been assessed.