Growth and survival of rohu, Labeo rohita (Hamilton) spawn fed diets fermented with intestinal bacterium, Bacillus circulans

Background. Because of the advancement of multiple spawning of carps, the importance of a quality larval diet is increasing day by day. The larval fish do not have the necessary enzyme or the amount of digestive enzymes to digest feed at optimum level. Therefore, fermentation of feed ingredients and/or formulated diets by bacterial enzymes to produce simpler forms of nutrients may be beneficial for them. Materials and methods. Five isocaloric (4.38 kcalּg-1) and isonitrogenous (35% crude protein approximately) experimental diets (D1-D5) containing 32% fish meal, 34% mustard oil cake, 30% rice bran, and 2% cod liver oil, were fermented in vitro with Bacillus circulans cells (at the rate of 108 bacterial cells per g) at 37oC for 1-5 day duration (1 day: D1, 2 days: D2, 3 days: D3, 4 days: D4, and 5 days: D5). The bacterial strain [extracellular enzyme producer Bacillus circulans (Lr 1.1)] used for fermentation was isolated from the intestine of rohu, Labeo rohita fingerlings. The reference diet (RD), containing same ingredients, was not fermented with bacterial cells. Rohu spawn (av. wt. 0.35 ± 0.01 mg) were fed ad libitum for 21 days in the laboratory condition at 30 minutes interval starting from 0900 h to 1600 h. Results. Fermentation of diets resulted in an increase in crude protein and free amino acid contents and decrease in crude fibre content. Diets D4 and D5 resulted in best growth and survival (98% and 98.33%, respectively) of rohu spawn compared to those fed with the reference diet (RD) and other experimental groups. A significant positive correlation was obtained between RNA : DNA ratio and specific growth rate (SGR) of 18 dietary groups (6 groups in triplicate). Conclusion. Fermentation of feed ingredients may be practiced as a tool for starter diet formulation to obtain better growth and survival of rohu spawn. The enzyme-producing strain, Bacillus circulans could be used to ferment diets for 4 to 5 days to increase the bioavailability of nutrients.