Evaluation of the Ability of GroBiotic-A to Enhance Growth, Muscle Composition, Immune Responses, and Resistance Against Aeromonas hydrophila in Nile tilapia, Oreochromis niloticus
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This study was conducted to evaluate the potential of graded levels of GroBioticA to improve performance of Nile tilapia, Oreochromis niloticus, fed a 29% crude protein (CP) diet. A 29% CP diet was formulated and supplemented with 0, 0.4, 0.8, and 1.2% GroBioticA and compared to performance of fish fed a 33% CP diet. Enhanced weight gain and feed efficiency were generally observed in fish fed the diets supplemented with GroBioticA compared to the 29% CP diet. No significant differences in these responses were observed between fish fed diets supplemented with GroBioticA compared to those fed the 33% CP diet. Supplementation of 0.8 and 1.2% GroBioticA induced significantly lower condition factor and hepatosomatic index compared to fish fed the 29% CP diet, but those values were similar to that of fish fed the 33% CP diet. GroBioticA supplementation and protein reduction had no effect on the viscerosomatic index of fish or moisture, lipid, and protein content of muscle samples. However, muscle ash increased significantly with protein reduction (29% CP diet), but GroBioticA supplementation (0.8 and 1.2%) reduced muscle ash content. Activities of catalase and superoxide dismutase were markedly reduced in fish fed GroBioticA (0.8 and 1.2%) compared to those fed the control diet. GroBioticA supplementation also induced significantly higher neutrophil oxidative radical production compared to fish fed the 29% CP diet, but no significant difference was observed in comparison with the 33% CP diet. After 8 wk of feeding, exposure to Aeromonas hydrophila for 3 wk resulted in 40% (0.4, 0.8% GroBioticA) and 27% (1.2% GroBioticA) mortality and reduced signs of disease, while 47% mortality was observed in fish fed the 29% CP diet. Based on the result of this study, it is concluded that 0.8 and 1.2% GroBioticA positively influenced growth performance and feed efficiency of tilapia fed diets containing 29% crude protein to levels comparable to fish fed the 33% CP diet. GroBioticA supplementation also significantly increased neutrophil oxidative radical production as well as resistance to Ae. hydrophila infection.
