Nile tilapia is crucial for food security and income in Uganda. However, the expanding aquaculture sector faces challenges, notably diseases and parasites including the zoonotic trematode Clinostomum, which threaten tilapia farming. Data on its prevalence in Uganda remains limited. This cross-sectional study evaluated the prevalence and mean intensity of Clinostomum species in farmed tilapia in Mpigi and Wakiso districts in the Lake Victoria Crescent aquaculture zone
Data was collected between December 2023 and January 2024 from 30 farms (23 ponds,7 cages) using semi-structured questionnaires and fish sampling. A total of 286 tilapia were harvested using seine and scoop nets: 216 from ponds and 70 from cages; 259 were Oreochromis niloticus and 27 O. leucostictus; 224 were male and 62 females; 134 fish were from Mpigi and 152 from Wakiso district. Necropsy examination was conducted on the sampled fish at the parasitology laboratory of College of Veterinary medicine, Makerere University. Clinostomum larvae were isolated and microscopically identified using morphological keys.
Among 286 tilapia, 86 Clinostomum larvae (yellow grubs) were isolated from 9 pond fish in 4 farms in Mpigi district, resulting in a 3.2% overall prevalence. Two species were identified: C. cutaneum (84 larvae, 2.8% prevalence) in skin tissue and C. complanatum (2 larvae, 0.4% prevalence) in the gill cavity of one fish (Figure 1). Prevalence differed significantly between tilapia species and districts (p<0.05). The overall mean intensity was 9.5 larvae, with C. cutaneum at 9.3 and C. complanatum at 2.0 (Figure 2). The mean intensity differed significantly between tilapia species (p<0.005). Therefore, implementation of control strategies is recommended, along with further research on the epidemiology and molecular confirmation of these species.