Technical evaluation of tilapia (Oreochromis niloticus) monoculture and tilapia-prawn (Macrobrachium rosenbergii) polyculture in earthen ponds with or without substrates for periphyton development

The effects of periphyton grown on bamboo substrate, on growth and production of Nile tilapia, Oreochromis niloticus (Genetically Improved Farmed Tilapia strain) in monoculture and polyculture with the freshwater prawn (Macrobrachium rosenbergii) were studied and economically evaluated. The experiment had 2 × 2 factorial design: The first factor was presence or absence of substrate for periphyton development, the second factor was related to culture system. The first system was monoculture of the GIFT strain of Nile tilapia stocked at 20,000 fingerlings ha¿ 1, the second system was tilapia¿prawn polyculture with each stocked at 20,000 fingerlings or postlarvae ha¿ 1. Bamboo poles were posted vertically in ponds under substrate treatments. Feed and inorganic fertilizers were applied to all ponds. There were no differences in phytoplankton biomass and primary productivity between the treatments (P > 0.05). The electivity indices indicated that there were low dietary overlaps between tilapia and prawn. Survivals of tilapia and prawn were higher in ponds with bamboo substrate (60% and 35%, respectively) than in the control ponds without substrates (55% and 20%, respectively). Addition of substrate significantly (P