Dietary yeast RNA supplementation reduces mortality by Aeromonas hydrophila in rohu (Labeo rohita L.) juveniles

A feeding trial was conducted for 60 days to delineate the effect of dietary ribonucleic acid or chitin on haematological parameters, phagocyte respiratory burst and resistance to Aeromonas hydrophila of Labeo rohita juveniles. One hundred and twenty-six (avg. wt. 13.40 +/- 0.17 g) juveniles were randomly distributed in six treatment groups, each one in three replicates. Six isonitrogenous (crude protein: 34.34-35.37%) and isocaloric (414-425 kcal 100 g(-1)) purified diets were prepared with different concentrations of either ribonucleic acid or chitin except the control group, viz., control, T1 (0.1% ribonucleic acid), T2 (0.2% ribonucleic acid), T3 (0.4% ribonucleic acid), T4 (25mg chitin kg(-1)) and T5 (50 mg chitin kg(-1)). Weight gain %, specific growth rate, feed efficiency ratio, protein efficiency ratio did not vary significantly (P > 0.05) among the experimental groups. Haemoglobin content and total erythrocyte count were observed within the normal range and were not influenced by the dietary immunostimulants. Highest total leukocyte count was found in the T3 group. The inummomodulatory effects of dietary immunostimulants were studied by using nitroblue tetrazoliurn (NBT) assay and serum parameters, namely total protein, albumin, globulin and A/G ratio. The respiratory burst activity (NBT) of blood phagocytes was highest in the T3 group followed by the T2 group, which varied significantly (P < 0.05) from other groups. Significantly (P < 0.05) higher total protein, globulin and lower A/G ratio was observed in the T3 group. The relative percent survival after challenging with Aeromonas hydrophila was highest in the T3 group, compared to the control group, followed by the T2 group. The results indicate that dietary ribonucleic acid at 0.4% enhances phagocyte respiratory burst and protection of Labeo rohita juveniles to challenge by A. hydrophila. (c) 2005 Published by Elsevier Ltd.