Influences of two types of substrates, natural (macrophyte, Pistia stratiotes) and artificial (plastic screen) were evaluated at 3 differrent densities (10, 20, 30%) on periphyton development, water quality and growth performance of jaraqui (Semaprochilodus insignis). Fish of average initial weight 1.46-1.69 g and length 4.15-4.26 cm stocked at 1/m 2 in 46 m 2 masonry tanks were grown for 120 days. The tanks were fertilized with urea, triple superphosphate and wheat bran. The types and densities of substrates tested did not drastically influence water quality. Natural substrate harboured higher periphyton biomass (1.48±0.09 mg/cm 2 ) as well as species diversity (28 genera) than the artificial substrate (0.84±0.12 mg/cm 2 , 20 genera). Fish in 10% and 20% artificial substrate and 20% natural substrate treatments showed better mean values of body weight (24.64, 23.86, 29.26 g respectively) on termination of the experiment. Fish survival was the lowest in 30% natural substrate (84.1%) and highest in 10% artificial substrate (94.2%). Higher fish biomass was recorded in 20% natural and 10% artificial substrate treatments (25.05 and 21.71 g/m 2 ), which amounts to a four-month yield of 250 and 217 kg/ha in the two treatments.