The partial replacement of fishmeal with mucuna seed meal in the diet of cultured juvenile Clarias gariepinus was tested over 70 days to determine their growth, nutrient and economic performance. The 25% fishmeal component of the control diet was replaced with 5–15% raw or processed mucuna seed meal and the fish were fed twice daily at 5% of their average body weight per day. The diet containing 5% raw mucuna seed meal resulted in the best specific growth rate (2.42% d–1), feed conversion ratio (2.05) and protein efficiency ratio (1.34), as well as the highest net profit of US$0.065 per fish and the best benefit-cost ratio of 1.32. The diet containing 15% processed seed meal produced the worst results. The processing of mucuna seed resulted in improved crude protein and ether extract and a 20% reduction in crude fibre.