Effects of substrate addition and supplemental feeding on plankton composition and production in tilapia (Oreochromis niloticus) and freshwater prawn (Macrobrachium rosenbergii) polyculture

This study investigated the effects of substrates and supplemental feeding on growth and production of tilapia (Oreochromis niloticus) and freshwater prawn (Macrobrachium rosenbergii) in a polyculture system. On actual farms, four treatments were evaluated in triplicate: substrate plus feed (herein called treatment SF), no substrate plus feed (S0F), Substrate plus no feed (SF0) and no feed and substrate (control). All ponds were stocked with tilapia and freshwater prawn juveniles at a stocking density of 30,000 ha(-1) with the ratio of 75% tilapia and 25% freshwater prawn. In the substrate-based system bamboo poles provided 60% additional surface area (compared to pond surface area) for periphyton growth. A commercial 25% protein diet fed at 2-3% tilapia body weight per day was applied. The feed conversion ratio (FCR) of tilapia was significantly higher in the treatment with substrate and feeding (SF) than in the treatment with only feeding (S0F). The combined net yields varied significantly (P <0.05) among four treatments and productions were 59, 48 and 47% higher in ponds with substrate and feed (SF), feed alone (S0F) and substrate alone (SF0), respectively, compared to the control. The combined net yields of tilapia and prawn in the treatments S0F and SF0 were similar (P>0.05). 29 genera of algae and 9 genera of zooplankton were identified from pond water and it showed significant (P <0.05) differences for Chlorophyceae, Bacillariophyceae and Cyanophyceae in the treatment SF compared to the control. There were no significant (P>0.05) differences for periphyton biomass in terms of ash free dry matter (AFDM), chlorophyll a and phaeophytin a in substrate-based systems. The net profit margin was highest in treatment SF0 (57%) followed by SF (5 1 %), S0F (50%) and the control (24%