Background. Carp fish offal contains high amount of protein and lipid. The quest for protein sources alternative to fish meal has been a priority in aquaculture research because of growing concerns on the future availability of fish meal for incorporation in fish diets. This study determined the extent to which carp fish offal could be fermented and used to replace fish meal in the formulation of diet for fingerlings of Labeo rohita. Materials and Methods. Fish offal, comprising viscera of carp, was fermented along with mustard oil cake and rice bran anaerobically by a microbial suspension (108 cells · mL-1) under ambient temperature (27-30°C). The fermented mixture was mixed with fish meal, mineral- and vitamin mixture to prepare three experimental diets: 1) a reference diet (T1), without any fermentation mixture, containing 40% fish meal, 2) a diet containing 25% fish offal (fermented) and 25% fish meal (T2), and 3) a diet containing 30% fish offal (fermented) and 20% fishmeal (T3). These diets were tested to evaluate growth and biochemical composition of the body of the fingerlings of Labeo rohita and apparent protein digestibility (APD) and intake rate of the diets by the fish. Proximate analysis of feed ingredients, experimental diets, faecal samples and the carcass were performed following the AOAC procedures. Results. Fingerlings of Labeo rohita, reared for 60 days with the diets containing fermented fish offal mixture (T2 and T3), showed higher growth and higher values of protein and lipid in the carcass than those reared with the reference diet (T1). Apparent protein digestibility of the diets did not vary significantly, but average feed intake rate of the T2 and T3 diets were higher than the T1 diet. Conclusion. Fermented fish offal is a viable alternative of fish meal in the formulation of diet for fingerlings of Labeo rohita. Fifty percent replacement of fish meal is possible by a mixture containing 30%fish offal. Further studies are required to improve quality of the fermentation mixture and increase the rate of replacement of fish meal.
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