Water quality and productivity of the traditional aquaculture system (whedos) in Oueme delta (Benin)

Abstract

In regard to improve the fish yield of the whedos (traditional fish ponds) by stocking and rearing during the draw-down period, we assessed their water quality comparatively to those of the Oueme River on which they depend. Variables such as pH, K₂₅, NO₂- and cladocerans density were similar in both systems while temperature, dissolved oxygen, transparency and microalgal biomass were significantly lower (P<0.05) in the whedos than the river channel. Using multivariate analyses, it was demonstrated that the variability of water quality in the whedos depends not only on their size but also on their width and water height. Moreover, many fish species were observed in the whedos (Clarias, Ctenopoma, Parachanna, Protopterus, Polypterus, Malapterurus, Xenomystus and Brienomyrus) and all display adaptations for survival in low dissolved oxygen conditions. The macrophytes were also abundant in the whedos and very diversified (24 species). In summary, the observations carried out in the whedos during this study show that the quality of their water limits consequently the possibilities to stock many fish species. However, potentiality of improving the fish yield of the whedos by stocking and rearing air breathing fish species during the draw-down period is currently debated.

Keywords : Whedo, fisheries management, water quality, plankton, fish stocking.