Lesion Profiles and Tissue Pathology of Clinostomum Metacercariae in Oreochromis niloticus From Lake Tana and An Adjacent Aquaculture Pond, Bahir Dar, Ethio
Gebyaw Menge Getnet, Mersha Chanie Kebede, Assaye Desta Amare, Ayenalem Shibabaw Atenaf, Assaye Wollelie Fentie, Hailu MazengiaABSTRACT
Background
Oreochromis niloticus is the most commercially important and widely cultivated freshwater fish species in Ethiopia due to its rapid growth rate, adaptability to different environmental conditions, tolerance to handling stress and high nutritional value. However, infection with Clinostomum metacercariae (MC) is a major problem for both aquaculture and wild fish populations and poses a significant zoonotic risk to human health.
Objectives
This study assessed the lesion profiles and tissue pathology associated with Clinostomum MC infection in 72 Nile tilapia fish collected from the southern Gulf of Lake Tana and adjacent ponds.
Methods
Using purposive sampling techniques, the purposive sampling strategy was utilized specifically for pathological and comparative burden profiling rather than estimating true population prevalence. The study design was cross‐sectional and conducted from January to May 2026. The Clinostomum MC were identified on the basis of their morphological features at the genus level. Parasite burden and histopathological lesions in the muscle, gill and liver were assessed using descriptive statistics and an independent t ‐test.
Results
The muscle exhibited the highest proportion of encysted MC among sampled fish (83.3%), followed by the gills (50%) and liver (36.1%). The total cyst burden was higher in fish collected from Lake Tana (239 cysts) than in the adjacent pond (57 cysts). Several gross and histological lesions were identified in the examined fish organs. Lamellar fusion (36.1%) and lamellar hyperplasia (33.3%) were the most common gill lesions, whereas the major muscle lesions observed were muscle fibre degeneration and disruption (66.6%) and cellular infiltration (33.3%). Sinusoidal dilation and congestion (13.88%) and hepatocyte vacuolation (11.1%) were the main microscopic lesions of the liver. The mean severity indices of gill, muscle and liver were greater in fish collected from Lake Tana compared to ponds. Among the examined organs, muscle was the most affected, followed by the gills, whereas the liver was the least affected. There were strong positive correlations between parasite burden and lesion severity indices in all examined organs.
Conclusion and Recommendations
The results indicate that Clinostomum MC cause significant tissue injury in Nile tilapia. Strengthening aquaculture farm biosecurity, snail control, regular surveillance, proper fish cooking practices and additional studies using molecular techniques and assessing seasonal variation are recommended to reduce the effects of the parasite on fish and its public health risks.