Histopathology Based Study of Nile Tilapia (Oreochromis Niloticus) Fish Species as a Biomarker for Water Pollution Evaluation in the Southern Gulf of Lake Tana, Ethiopia

Abstract In the past decade, the increasing distribution of pollutants in the aquatic environment have been observed and causing an integrative effects on the fishes. Likewise, due to anthropogenic activities southern gulf of Lake Tana is an impacted region and the production of Nile tilapia fishes is reduced. For this reason, the aim of this study was to conduct a histopathological based study of simple randomly sampled 48 Nile tilapia fishes’ health status at the southern gulf of lake-tana and aquaculture using a cross-sectional study from February 2023 to May 2023. The study evaluated the histopathology of gill, liver, gonads and spleen organs using a descriptive statistics accompanied with 2 x 2 contingency table and t-test analysis. During the study peroid different histological alterations were detected and the numbers of fishes affected by a specific histological alteration were presented as percentage prevalence, hence from the total fishes examined; hyperplasia (54.15%) followed by pigment deposits (52%), haemorhage (50%) and immune cell infiltration (50%) respectively, were the most frequently detected alterations, hoewever, Nile tilapias from the southern gulf of lake-Tana were 1.4 (odds ratio) times more likely showed histopathological alterations than those from the aquaculture although statistically, was not significant (p > 0.05). In addition, the study found, mean value of fish index (95.3) and regressive indices of gill (13.6), liver (14.8) and gonad (12.3); moreover, inflammatory indices of spleen organ (11.3) and mean severity grade value of gill (2.35) and gonad (1.7) organs respectively, were values obtained from the southern gulf of lake Tana and all those values were significantly higher (p < 0.05) from this site as compared to the aquaculture. In general, it has found tilapias from southern gulf of lake-Tana were showed higher pathological severity as compared with the aquarium. Among the four target organs evaluated, liver organs were observed the most damaged while gonads were the least impacted organs. Therefore, it has concluded that tilapia fishes are living under abnormal condition so to ensure sustainable fishery, water pollutant sources from Bahirdar city must receive proper attention and future studies should consider age differences, seasonal variation and detection of specific pollutants.