Diversity and Infection Levels of Metazoan Parasites of Oreochromis Esculentus and Protopterus Aethiopicus using Morphological and Molecular Characterization in Lake Kanyaboli, Kenya

Abstract

Kenyan lakes play a major role in fish supply and food security to the local communities and in promoting revenue in the country. Diseases and parasite infestations have been viewed as some of the major unfavorable factors limiting fisheries as they leads to decreased fecundity, retarded growth and mass mortality of fish. This adversely impacts on productivity and nutritional quality of fish. This study was conducted in Lake Kanyaboli between January and March 2024 to identify and describe or re-describe the metazoan parasites of endemic Oreochromis esculentus (Graham, 1928) and Protopterus aethiopicus (Heckel, 1851) in Lake Kanyaboli, Kenya. A total of 120 specimens, sixty of each fish species were collected using a fleet of gill nets of mesh sizes 2-5 inches and transported alive in plastic containers with the lake water. In the laboratory, the fish were euthanized through cervical disclocation and morphometric measurements, including total length (centimetres) mass (gram) and sex recorded. All fish samples were subjected to standard parasitological examination for ecto and endoparasites. Recovered parasites were preserved in 70% and 96% ethanol for morphological and molecular analysis respectively. Using light microscopy (LM) and scanning electron microscopy (SEM), two ectoparasites taxa, from O. esculentus and P. aethiopicus, were identified as: Dolops ranarum a branchuran copepod from the gill chambers, skin, fins and the mouth; an Hirudinean species (Batrachobdelloides tricarinata) from the skin and fins. An endo parasitic trematode, Heterorchis sp. from the intestine of P. aethiopicus was also identified. Sequences generated using 28S rDNA marker confirmed the identity of the D. ranarum and Heterorchis sp. when compared with those available in the database GenBank. This analysis revealed a 24 nucleotide base pair difference and an uncorrected genetic p-distances of 0.02 from H. cf. crumneficer (MW586924) retrieved from GenBank. Dolops ranarum recorded the highest prevalence, mean intensity and was the most diverse parasite of the two host species. A linear positive association was found between the host size and infection level of the three parasite taxa. However, the host sex factor was only associated with infections by B. tricarinata and Heterorchis sp. in P. aethiopicus. The morpho-genetic data in this study forms a parasitological baseline for future studies on these fish species and other hosts, not only in Lake Kanyaboli, but also in many water bodies within and beyond the Lake Victoria basin.