AimsTo develop a novel feed supplement for shrimp using pigmented spore-forming bacterial strains isolated from their gastrointestinal tracts. Methods and ResultsEight pigmented Bacillus strains were selected from the isolates based on high production of heat-stable spores, typical UV-Vis spectra of produced carotenoids (400-550nm), and free radical scavenging activity of their extracts. Of the eight strains, the red-orange pigmented Bacillus aquimaris SH6 was selected because it showed the highest abundance in shrimp guts (70% population). Whiteleg shrimp (n=30 per group) fed with SH6 spores, at >3x10(6)CFUg(-1)pellet for 4weeks had redder colour (score of 21-23 vs 20-22), 27-fold higher astaxanthin level (069 vs 025gg(-1) shrimp), 34% higher weight gain (718 vs 532gshrimp(-1)), and 85% higher phenoloxidase activity (OD490=0265 vs 0143) than shrimp in the control group. ConclusionsThe result supports the potential use of B.aquimaris SH6 as a feed supplement for promoting the colourization and weight gain, and for enhancing innate immunity of whiteleg shrimp. Significance and Impact of the StudyThis study demonstrates that carotenoids produced by B.aquimaris SH6 can be successfully absorbed and converted to astaxanthin in whiteleg shrimp.