Biofloc technology has recently gained attention as a sustainable method to control water quality, with the added value of producing proteinaceous feed in- situ. The present study was conducted to compare the effects of in-situ produced biofloc and externally added biofloc on water quality and growth of IMC (Catla, Rohu & Mrigal) under different stocking densities Experiments were carried out in FRP tanks (1000 L each) for a period of 90 days. The experimental design included in-situ biofloc, externally added biofloc and control treatments conducted at three different stocking densities (STD) - 25, 50 and 75 no. fish m-2 of surface area of tank respectively with each experiment replicated thrice. IMC of individual average weight 15± 1.6 g was reared in all treatments. In in-situ biofloc treatment, low protein (20%) commercial fish feed was added initially. Further, organic carbon in the form of wheat flour was added daily to maintain the C:N ratio at 10 . 60% extra carbohydrate applied in a typical in-situ biofloc tank. In externally added biofloc treatment, 50% of fish feed and 50% wet floc was added. The biofloc was produced in a 25 m3 cemented tank using aquaculture effluent from a nearby carp culture pond and maintaining the best C:N ratio of 10. In control treatment, high protein (30%) commercial fish feed was added. The harvested weights of fish in all treatments with different STD were found to be significantly different among each other (p < 0.05). Fish survival was 100% in all the treatments. The FCR values in in-situ biofloc treatment and externally added biofloc treatment were less compared to control treatment. Frequency of water exchange was significantly less in externally added biofloc treatment compared to other treatments.