Effects of Bacillus strain added as initial indigenous species into the biofloc system rearing Litopenaeus vannamei juveniles on biofloc preformation, water quality and shrimp growth

Abstract

The effects of Bacillus strains added as initial indigenous species into the biofloc system rearing Litopenaeus vannamei juveniles on biofloc preformation, water quality and shrimp growth under low salinity conditions were investigated. Three biofloc systems were designed (control, NT9 treatment with the addition of Bacillus subtilis NT9, and YB3 treatment with the addition of B. cereus YB3) for a 7-day biofloc preformation experiment and a 63-day shrimp culture experiment. The results showed that at the end of the biofloc-preformation stage, the biofloc volume in the YB3 treatment (13.6 ± 6.1 mL L−1) and control (7.1 ± 3.6 mL L−1) were 8.0 and 4.2 times that in the NT9 treatment (1.7 ± 0.7 mL L−1), respectively. During the culture experiment, the effects of strain YB3 on dissolved oxygen and total bacterial counts were significant (P < 0.05). The specific growth rates of shrimp in the NT9 treatment (4.25 ± 0.06% d−1) and YB3 treatment (4.03 ± 0.32% d−1) were increased by 22.8% and 16.5%, respectively, compared with that in the control (3.46 ± 0.69% d−1). No shrimp mortality was observed in the NT9 treatment. In the YB3 treatment, the survival rate of shrimp was 66.7 ± 21.1%, which was lower than that in the control (81.5 ± 16.4%, P > 0.05). The highest and lowest productivity were found in the NT9 treatment (3.14 ± 0.10 kg m−3) and YB3 treatment (1.85 ± 0.62 kg m−3), respectively. The addition of different Bacillus strains as initial indigenous species to the biofloc system had different effects. B. cereus YB3 promoted biofloc formation, and B. subtilis NT9 elevated shrimp growth performance.