To investigate the effects of Bacillus subtilis as water additive on gut microbiota in Spinibarbus caldwelli, Acrossheilus hemispinus and Hypophthalmichthys molitrix and its purification effect on aquaculture water, the gut microflora in the foregut, midgut and hindgut of three fishes were investigated through 16S rDNA sequencing and the pH, the levels of ammonia nitrogen and nitrite in the aquatic water were measured. The results suggested B.subtilis could reduce the contents of ammonia nitrogen by 46.39% in water stably since the 11th day and nitrite by 84.61% in water stably since the 19th day. The gut microflora in each intestinal site between experiment and control group were significantly different overall and the abundance of intestinal flora decreased in the experiment group. On the whole,in experiment group, the abundance of intestinal microbiota decreased and the phylum abundance of Actinobacteria and Planctomycetes increased and decreased, respectively. The genus levels of Bacillus increased while pathogenic bacteria Aeromonas and Vibrio decreased. The KEGG signal pathways showed that the metabolic functions of the H.molitrix were enhanced. This study showed that B.subtilis could reduce the level of ammonia nitrogen and nitritein in the aquatic water and purify the aquatic wate, while inhibiting the propagation of harmful intestinal microbiota and improving the metabolic level of intestinal microbiota in H.molitrix.

To provide technical support for artificial breeding of Pseudogobio vaillanti,the article explored the effect of starvation stress on the initial feeding and growth,and determined the point of no return(PNR)of early larvae.The changes of absorption of yolk sac,morphology,behavior,growth,survival and initial feeding rate of starved larvae were observed by methods of experimental ecology,and the PNR and optimized initial feeding time were determined.The results showed that under the water temperature of(25.5±1.2)℃,the larvae was started feeding at 4-day-old and the yolk sac was completely absorbed at 5-day-old.A period of mixed nutrition was only maintained 1 day.The initial feeding rate reached 100% at 5-6 days of age.The PNR of starved larvae occurred during 8-9 days of age with the interval between the first feeding to PNR was 4-5 days as the same time of 50% cumulative mortality rate for larvae of P.vaillanti.The total length had negative growth at 9 days of age.At 6 days of age,the body weight of starved group had negative growth and relative fatness decreased continuously,and it was significantly lower than that of control group,which could be used as judgment basis for the starved larvae of P.vaillanti.The results showed that the larvae of P.vaillanti had short mixed nutrition period and weak starvation tolerance.At water temperature(25.5±1.2)°C,the artificially bred larvae of P.vaillanti could be fed at 4-day-old.The best feeding time as 5-day-old,but the latest feeding time should not exceed 7-day-old.