Peuplements et biomasse zooplanctonique dans des etangs de pisciculture lagunaire (Layo, Côte d'Ivoire)

Abstract

Variation of physico-chemical parameters, phytoplankton biomass, and the composition and abundance of zooplankton were studied in brackish water pisciculture ponds after liming and filling. Two successive peaks of abundance were observed for both phyto- and zooplankton, followed by a decrease in biomass which then became more or less stable at lower values. The first zooplankton peak (2–2.5 g DW/m 3) was almost exclusively made up of rotifers and it occurred 8–10 days after liming. Crustacea developed later and dominated the second peak of abundance (1.2–1.4 g) occurring 13–20 days after liming. Total biomass then fell and fluctuated around 0.3 g. The distribution in size classes was estimated in terms of numbers and biomasses. It shows that the population of the ponds studied is composed mainly of small organisms in spite of the lack of predators. Results are analysed with regard to possible application in rearing fish larvae.