Effect of Halomonas storage poly‐β‐hydroxybutyrates on survival, growth and vibriosis resistance of half‐smooth tongue sole Cynoglossus semilaevis juveniles.

Half‐smooth tongue sole Cynoglossus semilaevis is a high‐value marine fish species. The intensive farming of this flatfish species has been suffered from disease outbreak. Poly‐β‐hydroxybutyrate (PHB) is a carbon storage compound accumulated by a wide variety of prokaryotes and is considered biocontrol agent applied in aquaculture. In this study, the dietary effect of PHB‐accumulating Halomonas (HM.PHB) was investigated on survival, growth, resistance on Vibrio anguillarum and intestine microbial composition of C. semilaevis juveniles. Halomonas was fermented, which contained 76% PHB on cell dry weight. The fish juveniles were fed formulated feeds containing 1% HM.PHB, 3% HM.PHB and 5% HM.PHB, and 3% particle PHB (Par.PHB) and 3% Halomonas containing no PHB (HM) for 6 weeks. The basal feed feeding was considered as the control. The results revealed that both Halomonas‐PHB and particle PHB significantly improved the survival and growth of the juveniles than the control (p <.05), while HM was in between. When challenged with V. anguillarum, the survival rate in 1% HM.PHB, 3% HM.PHB and 5% HM.PHB was significantly improved than the control. Moreover, the increased intestine fold, epithelium height and surface were also observed in 3% HM.PHB. PCoA based on high‐throughput sequencing of 16S rRNA gene fragment indicated that dietary Halomonas‐PHB and particle PHB modified and stabilized the intestine microbial community of the fish. Our study demonstrated that Halomonas‐PHB is an effective feed additive for C. semilaevis juvenile culture. The outcome of this study facilitates the application of Halomonas‐PHB in C. semilaevis and other marine fish aquaculture. [ABSTRACT FROM AUTHOR]