Growth and survival of rohu, Labeo rohita (Hamilton) spawn fed diets supplemented with fish intestinal microflora

Abstract

A 21-day feeding experiment was conducted to assess the effects of diets supplemented with fish intestinal bacteria producing extracellular enzyme on growth and survival of rohu, Labeo rohita (Hamilton) spawn (average weight 0.3 mg). Intestinal bacteria were isolated from healthy rohu fingerlings (average weight 3.51 ±0.31 g). Six isocaloric (4.24 kcal-g ) and isonitrogenous (approximately 35% crude protein) diets (D1-D6) were prepared containing 32% fish meal, 34% mustard oil cake, 30% rice bran, 2% cod liver oil, and 2% vitamin premix. Experimental diets (D2-D6) were supplemented with the isolated bacterial strain Bacillus circulans Lr 1.1 at five different levels (4 × 10, 4 × 10, 4 × 10, 4 × 108 and 4 × 1010 cells per 100 g of feed, respectively). Rearing of spawn on diet D5 (supplemented with 4 × 108 cells per 100 g) resulted in better growth and survival (97.33 ±1.15%) of rohu spawn compared to those with the control diet (diet D1, without any microflora supplementation) and other experimental diets. Diet D5 resulted in significantly higher growth and specific growth rate (SGR) followed by diets D6 and D4. RNA and DNA contents in the spawn were measured as an index of growth. The correlation coefficient (r value) of 0.831 and regression line having a slope of 0.79 suggested a significant positive correlation (0.01 level) between RNA-DNA ratio and specific growth rate.