MORPHOMERISTIC VARIABILITY OF Piaractus mesopotamicus IN ESTUARINE ENVIRONMENTS OF THE GULF OF GUINEA: IMPLICATIONS FOR STOCK IDENTIFICATION AND MANAGEMENT

Morphomeristic analyses, integrating morphometric measurements and meristic counts, remain indispensable for stock identification, population differentiation and ecological assessment in fisheries science, particularly in data-limited regions such as West Africa. This review synthesizes classical and contemporary literature on conceptual foundations, methodological approaches and applied relevance of morphomeristic studies, focusing on Gulf of Guinea estuarine ecosystems. The study examined Piaractus mesopotamicus (pacu), a South American characid increasingly introduced for aquaculture diversification, as a model for investigating morphological adaptation under novel estuarine conditions. Patterns of phenotypic plasticity, environmentally mediated morphological variation and complementary utility of morphometric and meristic traits in stock discrimination are critically evaluated. The synthesis highlights how estuarine environmental gradients including salinity, hydrodynamics, and anthropogenic pressures drive morphological differentiation in fish populations and how integrated morphomeristic frameworks effectively delineate management units where genetic data are scarce. For introduced P. mesopotamicus populations in Nigerian estuaries, establishing morphomeristic baselines is essential for monitoring adaptation, assessing ecological integration and informing risk management. The review underscores the relevance of multivariate statistical techniques PCA, DFA, cluster analysis and allometric corrections for robust population discrimination. Applications span fisheries management enabling stock specific conservation measures and aquaculture development, supporting broodstock selection and strain characterization. Key research gaps include limited baseline data, insufficient integration of environmental covariates and underutilization of advanced morphometric approaches for non-native species in West African estuaries. Strengthening morphomeristic research on introduced fishes will enhance evidence-based decision making for sustainable exploitation, responsible aquaculture expansion and ecosystem-based management in dynamic Gulf of Guinea estuarine systems.