The Ebrié lagoon undergoes numerous disturbances of anthropic origin manifesting since these last decennis by a massive and sudden mortality of the ichthyological populations. In order to measure the impact of these disturbances, length-weight relationship was estimated for the main ichthyologic species in the lagoon Ebrié. The specimens were collected from 457 identification, each sample was weighed to the gram and measured to average millimeter. For this study, 15 species belonging to 11 families were selected because of their presence during the sample period. The length-weight regressions were significant with a coefficient of determination (r²) ranging from 0.717 (Ethmalosa fimbriata) to 0.923 (Gerres eucinostomus). The allometry coefficient b is ranged from 2.36 for Tylochromis jentinki to 3.12 for Liza falcipinnis. The majority of the regression coefficient of the captured species (66.67%) was lower than 3. The size frequency distribution showed that 92% of the captured species are small in size with a minimum size of 30 mm for Gerres nigri and a maximum of 370 mm for Chrysichthys spp.
The impact of chemical pollution on organism’s characteristics was assessed through morphological features in IV and V sectors of Ebrié Lagoon using Sarotherodon melanotheron (Rüppel, 1852) as bioindicator. Sampling was carried out during a whole year in three sites (Layo, N’djem and Ahua) characterized by contrasted environments(respectively moderate, medium and high levels of pollution). The morphological studies were based on morphometric biomarkers such as fluctuating asymmetry (FA) and average body shape. Fluctuating asymmetry was evaluated among individuals within sites using ANOVA Procrustes. Average body shape was compared among sampling sites using Principal Components Analysis (PCA), Canonical Variates Analysis (CVA) and MANOVA. Fluctuating asymmetry did not vary between sampling sites. However, the average body shape was significantly different between specimens from Ahua and both those from Layo and N’djem. There was no significant difference between fish from Layo and those from N’djem.Allometric effects and the abiotic parameters influenced, to some extent, the body shape of individuals.A morphological differentiation according to the geographical distance was also observed. The study revealed a morphological adaptation of the populations of S. melanotheron in the study area.
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