article · Sustainable Aquatic Research
Farmed tilapia in Central Uganda can harbour parasitic digenean larvae known as Clinostomum species, which cause tissue cysts known as yellow grubs. A survey of twenty-three pond farms and seven cage farms across Mpigi and Wakiso districts examined 286 fish across two species, Oreochromis niloticus and Oreochromis leucostictus. Parasites were detected in nine pond-raised fish from four farms in Mpigi, while none were recorded in cage systems. Clinostomum cutaneum was the predominant species, predominantly infesting the skin, alongside rare occurrences of Clinostomum complanatum in gill cavities. Overall infection prevalence reached 3.2 percent, with Oreochromis leucostictus showing significantly higher vulnerability, displaying an 11.1 percent infection rate compared to 2.3 percent in Oreochromis niloticus. While female tilapia exhibited higher parasite counts than males, this difference was not statistically significant. The presence of these parasites indicates a need for targeted management strategies in regional aquaculture ponds.
Clinostomum infections lead to fish mortality, impaired growth, and visible yellow grubs that diminish fish marketability. Establishing infection levels helps fish farmers and fisheries officers understand local disease burdens in aquaculture ponds. Knowing which fish species are more susceptible enables producers to select more resilient stock and implement targeted hygiene and biosecurity protocols to protect farm productivity and food security.
This early-stage epidemiological research provides baseline disease data that can inform the development of parasite control protocols and farm management services for tilapia producers. Aquaculture extension services and fish health specialists could use the findings to design monitoring programmes and guide species selection in pond aquaculture. Commercial application currently remains at an early diagnostic stage, requiring further molecular validation and risk factor identification before preventative treatments or formal biosecurity products can emerge.
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Clinostomum species of fish cause economic losses through mortality, reduced growth, and diminished marketability. Yet, epidemiological data remains scarce in many developing countries on these digenean parasites. This cross‑sectional study assessed the prevalence and mean intensity of Clinostomum spp. in farmed Oreochromis spp. across 23 earthen pond and 7 cage farms in Wakiso and Mpigi districts, Central Uganda. A total of 286 tilapias (216 from ponds, 70 from cages; 259 O. niloticus, 27 O. leucostictus; 224 males, 62 females) were sampled. The fish were examined for Clinostomum larvae (metacercariae) using standard parasitology techniques in the laboratory at the College of Veterinary Medicine Animal Resources and Biosecurity, Makerere University. Eighty-six encysted yellow grubs were recovered in 9 pond fish from four farms in Mpigi District. Morphological analysis revealed 84 Clinostomum cutaneum larvae from the skin, and 2 Clinostomum complanatum from a gill cavity. The overall prevalence was 3.2% with a mean intensity of 9.5. Clinostomum cutaneum was the most common species with a prevalence of 2.8%, mean intensity of 9.3 while mixed infection with C. complanatum was at 0.4%. From the sampled tilapia, O. leucostictus showed a significantly higher prevalence and mean intensity of 11.1% and 23, respectively relative to O. niloticus at 2.3% and 2.8, respectively (p < 0.05). Female fish had a higher prevalence and mean intensity of 4.9 % and 12.7, respectively compared to the males at 2.7% and 3.3, respectively. However, these differences were not statistically significant (p > 0.05). Clinostomum spp. are therefore, prevalent in the study area, and appropriate control measures are required, as well as molecular confirmation of the species and risk factors associated with fish infections. Keywords: Aquaculture, Clinostomum, District, Metacercariae, Pond, Tilapia spp.
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DOI: 10.65869/sar.v5.i2.158
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