Background. Yeast extract powder (YEP) is a rich source of several B vitamins and is used mainly in bacterial culture. In the present study, the effect of dietary supplementation of YEP on growth, feed conversion, nutrient ADC, body composition, and digestive enzyme profile of rohu, Labeo rohita (Hamilton, 1822) fingerlings was evaluated. Materials and Methods. Rohu fingerlings (mean individual weight 1.76 ± 0.15 g) were fed, twice daily, fish meal-based 35% protein diets supplemented with YEP (0.1%, 0.2%, 0.3%, 0.4%, and 0.5% on dry matter basis) for 75 days at 3% of body weight, in triplicate. Fish performance in terms of growth, apparent nutrient digestibility, and whole body composition was studied. The intestinal protease and amylase activities were also determined in rohu fingerlings fed YEP-supplemented diets. Microbial cultures of the intestinal mucosa of the fish in all dietary treatments were carried out after the feeding trial in soybean-casein digest agar (TSA), gelatin-peptone (GP), starch (ST) and carboxymethylcellulose (CMC) plates, separately, to determine the protease- amylase-, and cellulase-producing capacities (qualitative) of the isolated organisms. Results. The fish fed YEP-supplemented diets exhibited better growth than the control up to 0.2% level. YEP at 0.1% level resulted in the best performance of the fish in terms of per cent weight gain, SGR, FCR, and PER, followed by the 0.2% level. YEP led to higher deposition of protein and lower deposition of lipid in the carcass. The intestinal protease activity was highest in the fish fed 0.1% yeast, followed by 0.2%. Protease-producing capacity of the intestinal bacterial flora in the in vitro cultures followed the same trend. Conclusion. It appears therefore that YEP in the diets might have some effect on the gut microflora by supplying additional digestive enzymes leading to better nutrient utilization.
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