Factors Influencing Zooplankton Production in Organically Fertilized Ponds for Culture of Paddlefish, Polyodon

Abstract

Zooplankton production was evaluated using either rice bran, distillers dry solubles, or a prepared diet as organic fertilizers in nine 0.02-ha earthen ponds. Each pond was inoculated with Daphnia pulex and stocked with larval paddlefish at 61,775/ha. Mean seasonal abundance and biomass of adult copepods was significantly higher (P ≤ 0.05) than cladocerans in each treatment. Mean abundance of cladocerans larger than 0.6 mm in total length was significantly lower (P ≤ 0.05) than cladocerans smaller than 0.6 mm in total length. Mean biomass of large cladocerans in PD ponds was signficantly greater (P ≤ 0.05) the biomass of large cladocerans in DS ponds. Large cladocerans were preferred food items by. paddlefish, compared to adult copepods or small cladocerans. Low Daphnia abundance after week 4 may have been caused by heavy fish predation, competition within the zooplankton community, potential algal toxicity, or elevated phosphorus. Rice bran or prepared diet were found to provide the best environment for Daphnia development during the study; however, paddlefish production in ponds fertilized with PD was about 3 times more expensive than production in ponds fertilized with RB.