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This field study was performed to demonstrate that Bacillus aquimaris SH6 spores administered as a feed supplement in adequate amounts confer beneficial effects to the whiteleg shrimp. Shrimps were administered either B. aquimaris SH6 spores at 1×106 CFU g-1 pellet (SH6 group) or a mixture of SH6 and B. subtilis SH23 spores at 5×105 CFU g-1 pellet for each strain (SH6-SH23 group). After a 28-day feeding period, the number of SH6 spores in the gut of whiteleg shrimp in the SH6 group and the SH6-SH23 group were 5.7×103 CFU gut-1 and 7.7×103 CFU gut-1, respectively. The total bacterial population of these two experimental groups increased about 10-75% compared to that of the control group. The astaxanthin level and red colour score were the highest in the SH6-SH23 group (1.66 μg.g-1 shrimp; 28-29), followed by the SH6 spore group (1.42 μg.g-1 shrimp; 27-28), and were the lowest in the control group (0.61 μg.g-1 shrimp; 26-27). Nevertheless, the growth rate of shrimps was similar (7.8-8%) among the three groups. In conclusion, feed supplements containing SH6 and SH23 spores co-effectively improved live counts and diversity of microbiota in shrimp guts, as well as improved astaxanthin level and red colour of whiteleg shrimps.