Application Of Bacterial PHB In Litopenaeus Vannamei Culture

According to statistic data issued by Food and Agriculture Organization(FAO),the global aquaculture production has exceeded to capture fishery,reaching more than 7000 tons in 2016.The aquaculture production in China ranks first in the world,accounting for 2/3 of the total world aquaculture production.However,poor management of intensive aquaculture usually led to outbreaks of aquatic diseases.Misuse of chemicals and antibiotics resulted environmental pollution,drug residues and increased drug resistance in aquatic animlas.Polyhydroxybutyrate(PHB)is a bacterial storage compound in non-equilibrium growth stage of bacteria which is used as carbon and energy sources.It has been reported that PHB improves the growth of aquatic animals and enhances their resistance to pathogenic bacteria,and thus it is a potential biological control agent in aquaculture industry.In this study,a strain of PHB-accumulated Halomonas was culture for 7 days in CM medium supplemented with glucose.PHB content in Halomonas cells reached about 70%dw.The effect of dietary bacterial PHB on survival,growth and disease resistance of two economic important aquatic speices Litopenaeus vannamei postlarvae and Cynoglossus semilaevis juveniles were studied.Bacterial PHB(HM.PHB)was fed to Litopenaeus vannamei postlarvae through Artemia nauplii enrichment.The groups fed non-enriched Artemia nauplii(Control),Artemia nauplii enriched with Halomonas containing no PHB(HM),and Artemia nauplii enriched with PHB particles(par.PHB)were used as controls.The results showed that bacterial PHB could significantly increase the survival rate and promote the growth of Litopenaeus vannamei postlarvae.After 14 days culture,the survival rate of HM.PHB group was 19%higher than that of Control,and the body length was increased by 1.9 mm.The challenge test indicated that bacterial PHB significantly increased litopenaeus vannamei postlarvae resistance to Vibrio anguillarum.The survival rate of HM.PHB.VB group increased by 19%compared with Control,(p<0.05).High throughput sequencing on intestinal bacteria showed that Firmicutes(63%)was the dominant plylum of HM.PHB.VB group,while Proteobacteria was dominant in other groups.Vibrio accounted for 63%in par.PHB.VB and 67%in Control.VB.It was noticed that in HM.PHB.VB,the proportion of Lactobacillus(11%)and Bacillus(16%)were higher than Vibrio(7%),indicating that bacterial PHB supressed the growth of Vibrio,but promote the growth of probiotic bacteria.In another trail,different amounts of bacterial PHB(1%,3%,5%)was supplemented in formulated diets and fed to Cynoglossus semilaevis juveniles.After 42 days culture,no significant difference were observed on survival,growth and vibrio resistance of fish juveniles when fed diets containing three levels of bacterial PHB(p>0.05).Vibrio challenge test showed that mortality of HM.PHB.VB decreased 68%when compared to control.VB group,indicating that bacterial PHB significantly improved the disease resistance of cynoglossus semilaevis juveniles.In conclusion,bacterial PHB can improve the survival,growth and Vibrio resistance of Litopenaeus vannamei postlarvae and cynoglossus semilaevis juveniles.The optimal amount of bacterial PHB was 0.3-0.4 g/L for Artemia enrichment and 1%dw for formulated feed.Bacterial PHB can supress the growth of Vibrio and promote the growth of probiotic bacteria.Generally bactierla PHB performed better than PHB particle.The results provide data for the application of bacterial PHB in aquaculture.