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¹ Visva-Bharati University, Department of Zoology, Fisheries Laboratory, Santiniketan 731 235, West Bengal, India DOI : 10.4194/trjfas.2011.0204 Viewed : 5162 - Downloaded : 7253 Nine isonitrogenous (30% crude protein approximately) and isocaloric (18.23 kJ g^-1) experimental diets (D1-D9) were formulated either with raw or treated (fermented with fish intestinal bacteria) Eichhornia crassipes leaf meal at 20%, 30% and 40% levels replacing other ingredients partially from a fish meal based reference diet (RD). Two specific strains of fish intestinal bacteria, Bacillus subtilis CY5 (isolated from Cyprinus carpio) and B. megaterium CI3 (isolated from Ctenopharyngodon idella) having extracellular cellulolytic and amylolytic activities, were used for fermentation of Eichhornia leaf meal for 15 days at 37°C. A commercial preparation of lactic acid bacteria (LAB), Lactobacillus acidophilus (Lactobacil) was used as feed supplement along with Bacillus subtilis CY5. Fermentation of leaf meal resulted in reduction of crude fibre, cellulose and hemicellulose contents and the antinutritional factors, tannin and phytic acid. However, free amino acids and fatty acids increased in the fermented leaf meal. The response of rohu fingerlings (4.0±0.14 g) fed the experimental diets for 80 days was compared with fish fed a RD. Both the inclusion level and type of Eichhornia leaf meal in diets significantly affected the growth performance of rohu. Fish fed diets containing 30% leaf meal fermented with CI3 strain performed better in terms of growth response, feed conversion ratio, protein efficiency ratio and apparent net protein utilization followed by diets containing 20% CI3 fermented leaf meal and 20% Bacillus subtilis + LAB fermented leaf meal in comparison with those with the RD. The apparent protein digestibility (APD) was better in fish fed diets containing fermented leaf meal. Highest deposition of protein in carcass was recorded in the group of fish fed 30% Bacillus subtilis + LAB fermented leaf meal diet whereas lipid deposition was highest in the fish fed the RD. It is concluded from the present study that Eichhornia leaf meal fermented with fish gut bacteria exhibiting extracellular enzyme activity can be recommended as a dietary ingredient in diets of Labeo rohita fingerlings up to 40% incorporation level replacing fish meal without any adverse effect on growth of the fish to produce cost effective formulated fish feed. Keywords : Eichhornia crassipes, Fish gut bacteria, fermentation, diets, growth, Labeo rohita fingerlings