Determination of body shape and meristic characters variations in wild and cultured populations of cichlid fish, Oreochromis niloticus, from the Republic of Benin, West of Africa

This study was designed to assess morphological changes between cultured and wild tilapia, Oreochromis niloticus (L.). Wild fish samples were obtained from fishermen operating in the waters of the vicinity of the province Parakou, Benin in November 2014, while the cultured samples were obtained from a fish farm in the municipality of Sô-Ava in the Atlantic region of the southern part of the Republic of Benin. Significant differences were observed in all nine morphometric traits measured. Discriminant analysis of morphometric parameters showed high divergence between the populations. The meristic count, however, overlapped broadly showing no divergence between the populations. The morphometric differences between the cultured and wild tilapia, O. niloticus, could have been linked to genetic differences or environmental factors or a combination of these.

Taking Stock of Genetic Concepts in Fisheries Management

The historical development of the idea of isolated stocks of fish that can be managed as separate management units has been as strongly tied to the intuitive idea of separate races as it has been to the practical necessities of jurisprudence and the estimation of both biomass and sustainable yield by fisheries managers. Demonstrating the existence of isolated fish stocks and delineating their boundaries has generally proved unsuccessful. Various techniques ranging from meristic count differences to polymorphic allelism have usually failed. However, in the pursuit of isolated stocks, biochemists have uncovered a great deal of information about the variation of polymorphic allele frequencies over time and space. Following the shift in opinion away from stochastic to natural selection mechanisms in allele frequency variation, it is evident that the observed variation in allele frequencies allows more insight into the biology of fishes than into the breeding structure of populations. These insights argue against the idea of isolated stocks of fish with homogeneous growth rates that are the basis of the sustainable yield models in favour of migration-linked stocks with heterogeneous growth rates.