Exploring the Effects of Seasonal Shifts and Climate Variability on the Physicochemical Properties and Morphological Adaptations of Nile Tilapia (Oreochromis niloticus) in the Great Kwa River, Nigeria: Implications for Ecosystem Resilience

Understanding how seasonal changes in water quality affect freshwater fish is essential for assessing ecosystem health and guiding sustainable fisheries management, especially in dynamic tropical river systems like the Great Kwa River in Nigeria. This study examined the influence of seasonal variations in physicochemical water quality on Oreochromis niloticus (Nile tilapia) populations in the Great Kwa River, Nigeria. Water and fish samples were collected over four months, encompassing both dry and wet seasons, to analyse key water parameters and fish morphological traits. Physicochemical analyses showed that most parameters, including total hardness (dry season mean: 102.60 ± 5.2 mg/L; wet: 98.33 ± 4.8 mg/L) and iron concentration (dry: 0.97 ± 0.12 mg/L; wet: 0.78 ± 0.10 mg/L), remained relatively stable across seasons, with no significant differences (p > 0.05). However, turbidity increased markedly in the wet season (dry: 345.50 ± 150 NTU; wet: 1242.50 ± 300 NTU), likely due to increased surface runoff, although this change was not statistically significant. Notably, cadmium concentrations declined significantly from 0.13 ± 0.02 mg/L in the dry season to 0.08 ± 0.01 mg/L in the wet season (t = 0.04, p < 0.05), suggesting potential environmental stress. Morphological assessments indicated consistent body weight (dry: 0.39 ± 0.05 kg; wet: 0.49 ± 0.06 kg; p > 0.05), total length, and fin dimensions between seasons, reflecting stable growth and nutritional status. In contrast, meristic traits such as ray count on the soft dorsal, pectoral, anal fins, and caudal peduncle showed significant seasonal variation (p < 0.05), possibly indicating adaptive morphological responses. The findings highlight the ecological resilience of Nile tilapia in a relatively stable environment, despite seasonal changes.