Succession Of Intestinal Microbiota Of Litopenaeus Vannamei Larvae And The Impacts Of Several Probiotics On Larviculture

In this paper,the changes of intestinal microflora in Litopenaeus vannamei larvae during larviculture period were firstly explored,and then the preventive effect of three Bacillus probiotics on luminescent vibriosis in shrimp larvae was studied.The effects of B.cereus on the bacterial community in the nursing water,as well as in intestinal tracts of larval and juvenile shrimp were investigated.And the effects of four microbial preparations on water quality of larviculture and the survival rate of postlarvae were evaluated.This paper will provide a basis for understanding the characteristics of the intestinal microflora of L.vannamei larvae,and will provide references for the rational application of probiotics in healthy larviculture and disease control of shrimp.The main research contents and results of this paper are as follows:1.The changes of intestinal microflora diversity and structural composition of L.vannamei larvae at 8 stages during factory and experimental larvicultures were explored by using high-throughput sequencing.The results showed that the larval intestinal microbiota presented a staged succession,especially from nauplius to mysis stages.The diversity and structural composition of larval intestinal microflora were significantly different between the two larviculture modes,but they tended to be consistent at postlarval stage.Proteobacteria and its Rhodobacteraceae,Bacteroidetes and its Flavobacteriaceae were commonly found in the intestines of healthy L.vannamei larvae.Ruegeria and an unclassified OTU1 of the Rhodobacteraceae could be used as indicators for healthy larvae.2.The control effects of B.subtilis GD1,B.licheniformis SD2,and B.cereus zou8 on luminescent vibriosis of L.vannamei larvae were compared through larviculture experiment.The results showed that under the condition of spontaneous infection with luminescent vibrio,compared with the control,zou8 treatment group could significantly inhibit the incidence of luminescent vibriosis and improve the survival rate of shrimp larvae(P<0.05).GD1 treatment group was the second most effective,while SD2 treatment group had no significant effect on the prevention of luminescent vibriosis.3.The effects of B.cereus zou8,which being added into larviculture water with 10 continuous days,on water quality,growth and survival of larval and juvenile shrimp were investigated.The effects of zou8 on aquatic and intestinal microbiota were analyzed by high-throughput sequencing.The results showed that zou8 had no significant effect on contents of ammonia nitrogen,nitrite nitrogen,phosphate and chemical oxygen demand in water.The larval vitality of zou8 treatment group was significantly higher than that of control group;and the survival rate of postlarvae were higher than that of control group.However,there was no significant difference in growth rate of body length in juvenile shrimp between the treatment and the control groups at 23 d and 44 d of culture,and there was no significant difference in survival rate at 44 d(P>0.05).zou8 had a viisble regulation effect on larval intestinal microflora,which was manifested in the relative abundances of Bacillaceae,Pseudoalteromonadaceae and Pseudomonadaceae increased obviously in treatment group.Additionally,the relative abundance of Vibrioaceae decreased significantly in treatment group at 44 d of culture.4.Based on the examination of two Bacillus(KC and DY)and two lactic acid bacteria(FC and ZW)preparations,the effects of the four microbial preparations on the water quality of larviculture and the survival of postlarvae were evaluated.The results showed that the four preparations were all composed of single pure species with high content.There were significantly higher contents of ammonia nitrogen,phosphate,and chemical oxygen demand in nursing water of the DY group than those in the control group,while the concentrations of nitrite nitrogen in the FC and ZW groups were obviously lower than that in the control at the early stage of larviculture(P<0.05).There was no significant difference in the survival rates of postlarvae among groups(P>0.05)with the exception in the DY group,which was significantly lower than that in the KC group at postlarvae 3 stage(P<0.05).However,the maximal survival rate and vitality of postlarvae were observed in KC group and the worst those in DY group.