Prevalence of fish parasites from Lake Hawassa, Ethiopia

An estimated 200 species of fishes of marine and freshwater fish are known to occur in Ethiopia. Fish parasites are the main cause of the significant threat to the fish biodiversity of Ethiopia's freshwater islands. Lake Hawassa plays a central role in the local economy of the city which supports the artisanal fishing sector. The parasite of the fishes at lake Hawassa are hitherto poorly known and there are limited reports on the type of parasites across different fish hosts such as size, age, sex, condition factor, or other biological or ecological traits.

A cross-sectional study was carried out in 2023-2024 to estimate the prevalence of fish parasites and host factors. In the current survey Oreochromis niloticus (n = 135), Clarias gariepinus (n = 87), and Labeobarbus intermedius (n = 43) were sampled. Internal and external organs was inspected for the presence of the parasite affecting their health and wellbeing. Some external parasites were extracted from the fresh water immediately after fish were caught. The randomly selected host was classified based on species, sex, body weight, and the total body length. Parasites are identified morphologically at genera level using standard identification keys and pictorial guide. Analysed data were presented as frequencies, percentages, mean intensity, and mean abundance. Chi-square and P-values were considered for statistical association.

The parasite distribution varies with sex, body weight, and standard length of the studied fish. The overall infection/infestation rate is 88.30% (n = 234). A total of 1748 parasites classified under Nematodes (e.g., Contracaecum), Digenean trematodes (e.g., Clinostomum, Euclinostomum, Diplostomum, encysted metacercariae), Monogeneans (Dactylogyrus), Myxozoans (Myxobolus spp.), Crustacean ectoparasites (Argulus, Dolops), Hirudinea (leeches)was collected from O. niloticus (788), C. gariepinus (642) and L. intermedius (318). The internal parasites recovered from O. niloticus were Clinostomum (65.16%), Euclinostomum (34.07%), Contracaecum (26.67%), and Diplostomum (24.44%). Higher number of Myxobolus species, leeches, Argulus, and Dolops species was also recorded. Digenean encysted metacercaria (68.97%) and Contracaecum species (50.57%) are the most common parasite species infecting C. gariepinus. Diplostomum species, Dactylogyrus species, leeches, Argulus species, and Dolops species pose a serious threat to fish health in lake Hawassa. The mean intensity of the parasites in L. intermedius, C. gariepinus and O. niloticus was found to be 8.59, 7.92 and 6.79 while mean abundance is 7.40, 7.37 and 5.84 respectively.

This study found that various body parts are contaminated with one or more parasites. Some of those parasites have established zoonosis or cause cross infection to other fishes requiring urgent cooperation in performing pre-stock assessment for optimal production and maintaining the heath of fishery and hence human being.