Fish often exhibit phenotypic plasticity by adapting their morphological traits to changing environments. In this study, the phenotypic plasticity of Sarotherodon galilaeus from three reservoirs (Aiba, Eko-Ende, and Asejire) in Southwestern Nigeria was assessed by evaluating their morphometric and meristic characters. Twenty-five morphometric measurements and six meristic counts were recorded in fifty samples from each reservoir. Morphometric measurements were standardised as a function of standard length, eliminating bias attributed to size. The meristic counts were not standardised because they are discrete and less influenced by size. One-way ANOVA was used to analyse morphometric and meristic data to test for significant differences between groups. The meristic and standardised morphometric datasets were further analysed using Canonical Variate Analysis (CVA) on R (candisc package). Significant differences (p<0.05) occurred within and between groups for 23 parameters among populations. The CVA plot revealed clear morphological differentiation among the three populations at 95% confidence ellipses, but the meristic data could not delineate the populations. Therefore, the three populations of S. galilaeus exhibited a significant degree of phenotypic divergence based on their morphometric traits, likely driven by geographic isolation and local adaptation to the unique environmental conditions of each reservoir.