A 90-day experiment with 2 x 2 factorial design-2 levels of substrate (with and without) and 2 levels of feeding (with and without)-was carried out in 16-m(2) outdoor cement tanks having 5-cm soil base, to evaluate the performance of Labeo fimbriatus in polyculture with Catla catla in periphyton-based culture system with sugarcane bagasse as the substrate. Advanced fingerlings of L. fimbriatus (av. length 19.1 cm and weight 16.81 g) and C. catla (av. length 20.5 cm and weight 11.70 g) were stocked in tanks at a density of 10,000 no./ha in 6:4 ratio. Treatments included no feed, no substrate (NFNS); substrate (S); feed (F); and substrate + feed (S + F) treatments, each tried in triplicates. Sugarcane bagasse was hung vertically at 2 t/ha in S and S + F tanks. Fish in the treatments F and S + F only were fed daily a formulated pelleted feed (25\% crude protein and 6\% fat) at 5\% of fish biomass. Estimation of periphyton biomass and total pigment content was done once in 15 days. Representative fish samples were analyzed for carcass biochemical composition and activity of gut digestive enzyme-total protease, trypsin, chymotrypsin, carboxypeptidase A and B, amylase, lipase, and cellulase-at the end of the growth trial. The weight gains of L. fimbriatus in F (65.05 g) and substrate added tanks (62.75 g in S and 76.48 g in S + F), at the end of the rearing period, was comparable. The weight gain of catla was similar in NFNS (69.17 g) and S treatments (75.25 g) and lower compared to F (100.63 g) and S + F tanks (100 g). While higher moisture and lower crude protein content were observed in the carcass of L. fimbriatus (estimated at harvest) under NFNS treatment, these parameters remained similar with other treatments. In C. catla, S + F recorded the highest crude protein content, with similar values under other treatments. Excepting cellulase in hepatopancreas, the activity of all other enzymes in C. catla showed a pattern corroborating the growth trend, with lower values in NFNS treatment. While the activity of enzymes was higher in fed C. catla compared to the unfed ones, in L. fimbriatus, the activities in all the three treatments were comparable and higher than that recorded in fish under NFNS treatment. The growth performance of L. fimbriatus in polyculture with C. catla in periphyton-enhanced culture system was comparable with those maintained under supplementary feeding, indicating the utility of periphyton enhancement in polyculture.