Effects of a yeast-based additive on growth and immune responses of white shrimp, Litopenaeus vannamei (Boone, 1931), and aquaculture environment

A 60 days feeding experiment was conducted to determine the effects of YK-6 (a yeast culture feed supplement) on growth and immune responses of white shrimp, Litopenaeus vannamei and aquaculture environment in commercial scale farms composed of nine ponds. Three treatments (control, Diet 1 and Diet 2) were designed to contain YK-6 levels of 0.0, 1.0 and 1.5 g kg^-1 respectively. At the end of the test, the mean production of Diet 1 (0.649 ± 0.030 kg m^-2) and Diet 2 (0.648 ± 0.033 kg m^-2) were significantly higher than that of the control by 29.5% and 29.3% respectively. The feed conversion ratio decreased significantly by 12.3% (Diet 1) and 8.5% (Diet 2) compared with the control group respectively. The environmental indices indicate that the quality of water and pond sediment was improved. The endotoxin concentrations, the number of Vibrios and heterotrophic bacteria in the shrimp intestine of the treatment groups were significantly lower than that of the control, particularly in the later stage of the farming period. The YK-6 extended positive effects on growth, improved sediment quality, reduced endotoxin in shrimp intestine, and enhanced activities of lysozyme and phenoloxidase.