Effects of stocking density, periphyton substrate and supplemental feed on biological processes affecting water quality in earthen tilapia-prawn polyculture ponds

Abstract

The technical and economic potentials of tilapia, Oreochromis niloticus (L.), and giant river prawn, Macrobrachium rosenbergii (de Man), polyculture in periphyton-based systems are under investigation in an extensive research programme. This article is a combined analysis of data from four experiments exploring the effects of periphyton, fish, prawn and feed on water quality. Factor analysis and ancova models applied to the combined dataset allowed to identify the underlying ecological processes governing the system, and construct conceptual graphic models of the periphyton?environment relationships observed. With the first factor, variability in water quality was due to autotrophic (photosynthesis and nutrient uptake) and heterotrophic (respiration and decomposition) processes affecting water quality in opposite directions. With the second factor, variability was related to decomposition on the bottom and nutrient release into the water column, algae production and sedimentation. The analysis of the relationships between both factors and the growth rates of tilapia and prawn in the different systems allowed a better understanding of the functioning of tilapia?prawn ponds, and indicates that their joint culture is technically feasible and economically viable. Therefore, this technology is recommended for poverty alleviation and nutritional security in rural Bangladesh as well as in other countries of the region.