Author(s): Kouadio Atto Delphin, Groga Noël, Konan Kouakou Seraphin, Ndjouondo Gildas Parfait and Salla Moreto

Abstract: The influence of agricultural by-products inputs to juveniles of Oreochromis niloticus on phytoplankton composition and density in rice-fish ponds was assessed from water samples collected between April 10 to July 18, 2019. The experiment was carried out in four types of rice-fish ponds, namely, ponds without exogenous food input (RC), ponds with maize bran input (RSM), ponds with rice bran input (RSR) and ponds with various agricultural by-products combined input (RPC). Phytoplankton sampling was carried out by filtering 45 litres of water using a 20 µm plankton net with a 20 µm void and environmental parameters that could influence phytoplankton blooms were determined in situ. A total of 194 taxa divided into five phytoplankton phyla and 51 genera were inventoried. Species richness was higher in the RSM and RPC ponds than in the others with 101 and 92 taxa, respectively. Mean phytoplankton density was significantly higher in rice-fish ponds RPC (60.6 106 Individuals/L) and RSM (55.1 106 Individuals/L) with a strong dominance of Chlorophyta and Euglenophyta. These high densities were positively correlated with high nutrient concentrations.

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