Assessment of histopathological changes of Oreochromis mossambicus from Beira lake and Ihalagama lake in relation to water quality parameters

Abstract

Water quality of urban lakes is compromised by urbanization-induced pollution leading to water quality deterioration. Oreochromis fish are used as biomarkers due to their resilience to different environmental and chemical conditions. This study focused on histopathological changes in gills and livers of Oreochromis mossambiccus under different water quality conditions. Two Sampling locations were selected: Beira Lake, Colombo and the Ihalagama Lake, Ragama. The main objectives were to compare the physicochemical parameters of the water of two water bodies and the histopathological changes in O. mossambicus between the two lakes. Monthly water samples of two sites from each lake (n=3) were collected from September 2023 to February 2024. Water quality assessment was done based on both in-situ and ex-situ parameters. Data analysis was conducted using One-way ANOVA with the Tukey's pairwise comparison using MINITAB 14.0. Significant spatial variations were recorded in Beira Lake (P<0.05) including significantly higher conductivity (185.76 μS/cm), nitrates (1.73 mg/l), phosphates (1.07 mg/l), chemical oxygen demand (633.0 mg/l), and biological oxygen demand (7.30 mg/l) than Ihalagama Lake. Ihalagama Lake had lower mean concentrations for nitrates (0.47 mg/l), phosphates (0.15 mg/l), chemical oxygen demand (238.80 mg/l), and biological oxygen demand (2.46 mg/l). Fifteen fish samples from each lake, with an average weight of 132.20 g were collected using a net. The paraffin method was used in histopathological analysis of fish tissues. Fish of Beira Lake exhibited severe gill abnormalities (>50%) including deformed pillar systems, epithelial hyperplasia, lamellae fusion, and telangiectasia. Liver histopathology indicated severe blood congestion and Melano macrophage centres (>50%). In contrast, fish sampled from Ihalagama Lake displayed minor aberrations in gill and liver histopathology (<10%). This study reflects the ecological impacts of deteriorating water quality from sewage, municipal waste, and fertilizers. These pollutants cause nutrient enrichment and uncontrolled algal blooms, leading to hypoxic conditions, adversely affecting aquatic life. In response, fish gills display histopathological changes to improve oxygen uptake and as defensive mechanisms to thrive in polluted waters. This study concludes that histopathological changes in O. mossambicus is an effective biomarker for monitoring water quality deterioration in aquatic ecosystems.