PHENOTYPIC AND GENETIC DIVERGENCE IN SOME CICHLID POPULATIONS FROM TWO SELECTED BRACKISH WATER BODIES IN BENIN REPUBLIC AND NIGERIA

Abstract

For sustainable management of fish resources, an understanding of the adaptive capacity and population
structure of species is important. However, there are still limited data on tilapine variations across West African
lagoons. The morphological and genetic differences in Oreochromis niloticus, Coptodon guineensis, and Tilapia
mariae populations were investigated in Porto-Novo Lagoon (PNL), Benin, and Epe Lagoon (EPL), Nigeria, to
determine their heterogeneity. For eight months, from December 2022 to July 2023, 188 fish samples were
collected (EPL: 43 O. niloticus, 29 C. guineensis, 17 T. mariae; PNL: 44 O. niloticus, 30 C. guineensis, 27 T.
mariae) and analyzed for meristic attributes (MRA), morphometric attributes (MPA), phenotypic heterogeneity,
and genetic diversity using cytochrome b (Cyt-b) gene sequences. For MPA, the coefficients of variation ranged
from 9.33% to 33.25% in O. niloticus, 6.18% to 32.22% in C. guineensis, and 7.19% to 39.58% in T. mariae,
pointing to substantial inter-population variability. From genetic analyses, O. niloticus populations in PNL were
more closely related to the Coptodon aff. louka 'Samou' strain than EPL counterparts; PNL C. guineensis
clustered nearer to Oreochromis niloticus haplotype HAP14 and Oreochromis niloticus Asejire12 than EPL
populations; and T. mariae from PNL showed closer affinity to Bathybates graueri from Lake Tanganyika than
EPL. It can be concluded that there are significant phenotypic and genetic divergence between the lagoons,
affirming the need for location-specific conservation and management to sustain biodiversity.