Results of a cage aquaculture experiment conducted in Charan beel (a floodplain wetland), district Morigaon, Assam, India to determine optimum stocking density of Labeo rohita fry are discussed. Locally available bamboo and other low-cost construction materials were used for constructing a battery of ten cages (individual cage dimensions 2 × 2 × 2 m and effective water volume 6 m3). Labeo rohita fry (average length 4.0 ± 0.04 cm, average weight 1.05 ± 0.03 g) were stocked at five different stocking densities, viz. 50 (SD1), 100 (SD2), 150 (SD3), 200 (SD4) and 250 (SD5) fry/m3 with two replicates each. Reared fry were fed twice daily with a formulated feed containing 33.16 % crude protein for 2 months. The physico-chemical parameters of sediment were not significantly (p > 0.05) affected by stocking density. Different stocking densities significantly (p < 0.05) affected the growth parameters of reared fish. The final weight, weight gain percent and specific growth rate were highest in the lowest stocking density of 50 fry/m3. These responses remained unaffected (p > 0.05) at SD2 to SD4, but at SD5 there was significant reduction of growth. Feed conversion ratio, protein efficiency ratio, apparent net protein utilization and energy retention value were adversely affected with the increase in stocking densities. The net benefit and benefit-cost ratio were highest in SD4. Therefore, economics of cage culture was considered as the most important criterion in judging SD4 (200 fry/m3) to be the optimal stocking density for raising L. rohita fry in cages in seasonally open floodplain wetlands of Assam, India.
