The objective of the current study was to evaluate the growth performance, survival, feed utilization, whole body composition and biochemical blood parameters of Nile tilapia, Oreochromis niloticus and thinlip mullet, Liza ramada, fed diets supplemented with four levels of lemon peel (0, 0.5, 1 and 2%) in a polyculture system. The fish were stocked in 2×5×1 m concrete tanks at a density of 40 Nile tilapia (0.6 g) and 10 thinlip mullet (3.3 g) fingerlings per tank and were fed a pelleted diet (~25% Crude protein), twice daily for 77 days. Treatment with 2% lemon peel had significant positive effects on growth, feed utilization and total biomass of Nile tilapia, whereas 0.5% lemon peel was optimal for thinlip mullet. The blood parameter results showed thatNile tilapia fed 2% dietary lemon peel had the lowest triglyceride, amylase and glucose levels. In contrast, thinlip mullet fed 0.5% dietary lemon peel had the highest levels of amylase and glucose compared with the other groups.