Influence of the Quality of Maintenance of Fish Ponds on the Biomass of Zooplankton in situ in Tropical Zone (Yaoundé-Cameroon-Central Africa)

A comparative study of the biomass of zooplankton of four semi-intensive fish ponds found in the ecological area of Yaounde in Cameroon was sampled for 9 months, which made it possible to evaluate the influence of the maintenance quality of the water bodies on their productivity. There were three ponds E1, E2, and E3 fertilized with organic and mineral matter, sampled from March to November 2012 on the one hand and on the other hand an experimental pond ET serving as a control, which was sampled from March to November 2014. ET was fertilized with mineral and organic matter and received particular attention during the first three months of breeding. The breeding method recommended in these ponds was the polyculture of Clarias gariepinus and Oreochromis niloticus. The samples were collected twice a month at 20 cm depth. Physico-chemical and biological analyses were measured using appropriate techniques. Zooplankton biomass remained very high in ET relative to E1, E2 and E3 (90% vs. 10%), creating an uneven profile in all water bodies. Minimum biomass values were 119 mg C / L in E1, 200 mg C / L in E2, 40 mg C / L in E3 and 781 mg C / L in ET; the maximum values being 748 mg C / L, 2643 mg C / L, 474 mg C / L and 67010 mg C / L in E1, E2, E3 and ET respectively. The largest contributors to this biomass were rotifers followed by Cladocerans in ET and E2 and Copepods followed by rotifers in E1 and E3. Food resources were thus limited in these last two water bodies compared to others. Abiotic and biological analyses indicate that these water bodies were oligomesotrophic (E1 and E3), mesotrophic (E2) and eutrophic (ET). ET under these conditions enabled the production of a satisfactory fish yield. It is therefore recommended that, fish farmers should improve the quality of maintenance of fish ponds which together with good fertilization will generate maximum productivity.