Effect of Bacillus sp. Supplementation Diet on Survival Rate and Microbiota Composition in Artificially Produced Eel Larvae (Anguilla japonica).

This study was performed to investigate the effect of microbial supplementation diet on the survival rate and microbiota composition of artificially produced eel larvae. Microorganisms supplemented in the diet were isolated from wild glass eel intestines and identified as Bacillus sp. through 16S rRNA sequencing analysis. In vitro tests confirmed that the strain had no hemolytic activity and virulence genes. Microbial supplemental feeding significantly increased the survival rate of artificially produced eel larvae for 30 days post-hatchling compared with that of the control group. It also caused changes in the α-diversity, ß-diversity, and relative abundance of the bacterial communities. Analysis via phylogenetic investigation of communities by reconstruction of unobserved states predicted that these microbial community changes would significantly increase the carbohydrate metabolism, membrane transport, and cellular community pathway of the microbial supplementation group. Therefore, microbial supplementation feeding for eel aquaculture could increase the viability of artificially produced eel larvae and alter the microbial composition to induce metabolic changes.

Synergistic effects of dietary Bacillus sp. SJ-10 plus ß-glucooligosaccharides as a synbiotic on growth performance, innate immunity and streptococcosis resistance in olive flounder (Paralichthys olivaceus).

Bacillus sp. SJ-10 (BSJ-10) was identified from traditional Korean fermented fish, the previously recognized prebiotic ß-glucooligosaccharides (BGO), and their combination as a synbiotic were prepared to evaluate their individual and synergistic effects in olive flounder (Paralichthys olivaceus). Four diets (one control and three treatments) were formulated containing neither BSJ-10 nor BGO (control), 1 × 108 CFU g -1 BSJ-10 (BSJ-10), 0.1% BGO (BGO), and 1 × 108 CFU g-1 BSJ-10 + 0.1% BGO (BSJ-10 + BGO). Triplicates of 15 fish (weight 10 ± 0.25 g) were randomly allocated to the four diet groups and fed one of the diets for 8 weeks. At the end of the experiment, fish weight gain (WG), specific growth rate (SGR), feed conversion ratio, and protein efficiency ratio in BSJ-10, BGO and BSJ-10 + BGO diets were positively modulated (P < 0.05) compared with control. Specially, WG and SGR were significantly (P < 0.05) higher in BSJ-10 + BGO than that of BSJ-10 and BGO (individual component). The innate immune parameters such as respiratory burst, superoxide dismutase, and lysozyme activity (LSZ) of fish fed BSJ-10 and BSJ-10 + BGO (both groups) were significantly (P < 0.05) higher than the control. Moreover, myeloperoxidase activity (MPO) and LSZ of fish fed BSJ-10 + BGO were significantly higher compared with individual component. Compared with control, intestinal BSJ-10 content, expression of interleukin (IL)-1ß in liver and kidney, and tumor necrosis factor (TNF)-α in liver were higher in both groups, but microvillus length was increased (P < 0.05) only in BSJ-10 + BGO. During in vivo challenge experiment with Streptococcus iniae (1 × 108 CFU ml-1), survival rate of fish was significantly higher in all treatment groups versus control. Moreover, in BSJ-10 + BGO, protection against S. iniae infection and transcription of TNF-α and IL-6 in gill were significantly (P < 0.05) higher than the individual component. Collectively, an improved WG, SGR, MPO, LSZ, transcription of IL-6 and TNF-α, and cumulative survival rate against streptococcosis clearly demonstrates a synergistic outcome of diet BSJ-10 + BGO as synbiotic in olive flounder.