Effects of dietary supplementation of probiotics on growth, immune responses, and gut microbiome of the abalone Haliotis diversicolor

There is growing interest in the use of probiotics as an alternative strategy for the promotion of growth rates and prevention of diseases in aquaculture. In this study, abalone Haliotis diversicolor were fed with different probiotic-supplemented diets for 180 days, containing Bacillus stratosphericus A3440, Phaeobacter daeponensis AP1220, and a mixture of the two strains. Probiotic supplementation significantly increased shell length and wet weight of juvenile abalone (p < 0.05). Compared with those non-treatment group, trypsin and lipase activities were increased significantly in the gastrointestinal tract of animals fed with A3440 or bacterial mixture (p < 0.05). A subsequent ten-day of challenging trial against Vibrio harveyi, the animals with AP1220 had similar to 90% survival rate as against similar to 60% survival rate for the non-treated animals. Likewise, in situ glutathione peroxidase, catalase, alkaline phosphatase, acid phosphatase, and superoxide dismutase assays showed that the probiotics significantly improved immune response of H. diversicolor (p < 0.05). 13,622 OTUs were obtained from abalone intestine microbiome by 16S rRNA high-throughput sequencing. Microbial diversity indices and richness estimates in the non-treated group declined before and after Vibrio infection trial. Conversely, these indexes enhanced to different levels in probiotics treatments, and the A3440 group restored and reached the highest value. Cluster analysis showed that probiotic could re-establish and subsequently balance the gut microbial community after the challenge trial. Furthermore, these potential probiotics had a positive effect on the number of beneficial endogenous bacteria in the abalone gut, such as bacilli and actinobacterial species. Thus, dietary administration of B. stratosphericus, P. daeponensis and their mixture could improve the nutrient and health status of abalone H. diversicolor.