Ichthyofaunal diversity and the impact of anthropogenic activities on fish population assemblages were studied in Lake Cayo, a small lake located in the coastal region of the Republic of Congo. Twelve stations were sampled twice over a two-year period. Fishing techniques following standardized methods utilizing monofilament gill nets, and nine environment variables were measured at each station. A total of 11,361 specimens comprising 30 species in 28 genera and 18 families were collected with the Cichlidae being the most diversified. Redundancy Analysis with forward selection coupled with Monte Carlo permutation tests identified depth, pH and substrate as accounting for 57.7% of the total variance among the nine variables sampled (p < 0.05). The low Shannon's diversity (1.16 ± 0.33) and Equitability (0.43 ± 0.12) indices at all sites, suggest that the Lake Cayo system is in poor ecological health.

This study was initiated with the aim of studying the diversity and spatio-temporal distribution of fish in the Malonda lagoon, one of the coastal ecosystems of the Base Guinea in the Republic of Congo. The fish were sampled over a period of two years in three zones each including three stations known as: Mangrove, Grass and Full water. One station upstream towards the freshwater zone, one station downstream towards the mouth and one station in the containment zone. The catches were made using monofilament gillnets of 8, 10, 20 and 30 mm mesh size. During the rainy season, 1516 specimens belonging to 29 species, 17 families and 12 orders were collected. In the dry season, 768 specimens belonging to 20 species, 11 families and 8 orders were collected. For both seasons, the family Cichlidae is the most diversified. The marine forms are the most represented compared to the continental forms. Redundancy Analysis with forward selection coupled with Monte Carlo permutation tests showed that in the rainy season four variables influenced the distribution of species (Depth: 48%, Vase: 16%, Nitrogen: 10% and Transparency: 10%); in the dry season three variables influenced the distribution of species (Vase: 38%, Nitrogen: 14% and Oxygen: 11%). Ecological indices showed that the Malonda lagoon is already undergoing either anthropic or natural impacts, its state of ecological integrity is disturbed, the values of Shannon diversity and Equitability indices are not close to maximum values. The results of this study will serve as an ecological database for the proper