When fish have only access to formulated feed, the optimal dietary protein to energy ratio (P:E) for tilapia ranges between 18 and 23 g.MJ^-1. In pond culture, where natural foods complement administrated feed, increasing the carbon:nitrogen (C:N) ratio stimulates the natural food productivity. This study assessed if lowering the dietary P:E ratio (and thus increasing the C:N ratio of the feed input in the pond) below the optimal P:E ratio affects fish productivity, food web dynamics and nitrogen balances in semi-intensively managed tilapia ponds.