OCCURRENCE OF CYSTACANTHS OF POLYACANTHORHYNCHUS-KENYENSIS LARVAE (ACANTHOCEPHALA) IN 4 TELEOSTEAN FISHES FROM A TROPICAL LAKE, LAKE-NAIVASHA, KENYA

From January 1992 to December 1993, a total of 2158 fish, namely Oreoc hromis leucostictus (Trewavas, 1983), Micropterus salmoides (Lacepede, 1802), Tilapia zillii (Gervais, 1848) and Barbus amphigrama (Boulenge r, 1902) were sampled from thirteen stations on Lake Naivasha, Kenya, using a fleet of gill nets and examined for helminth parasites. The pr evalence of infection due to cystacanths of an acanthocephalan, Polyac anthorhynchus kenyensis Schmidt et Canaris, 1967 among parasitized O. leucostictus ranged from 30.4 to 86.9%; among T. zillii from 4.1 to 77 .7%; in M, salmoides from 20 to 50%; and in B, amphigrama from 5.8 to 100%. In 735 hosts belonging to the above four species, a total of 419 8 immature specimens of P. kenyensis were recovered. All cystacanths w ere found in extraintestinal sites, either free within the fish body c avity or encysted within the host visceral organs. There was no signif icant variation in the prevalence of the parasite within months (P > 0 .001). Host sex ratio was significant (P < 0.001) in favour of male T. zillii, and also highly significant (P < 0.001) in favour of male O. leucostictus. Moreover, in this fish, prevalence of infection was obse rved to increase with the increase in the size of the fish. Among infe cted M. salmoides, there was no significant departure from a 1 : 1 sex ratio.