A 42-day study was conducted where prawns (0.32 g) were fed diets where 0, 20, 50, 75 and 100 g (100 g)⁻¹ of fish meal was replaced by soya bean meal (SBM). Feed intake was not significantly affected by inclusion of SBM, while specific growth rate and conversion efficiency decreased with increasing dietary SBM. Standard metabolic rate was significantly affected by dietary soya bean level, and was the highest in the 75 g (100 g)⁻¹ SBM group. Carcass dry matter, crude fat and energy value declined with increasing SBM inclusion. SBM, without supplementation of amino acids or other additives, was not suitable as a major protein source in freshwater-prawn diets.