Effect of Picochlorum on water quality, shrimp production and microbial community in the culture of Litopenaeus vannamei

Abstract

Abstract To evaluate the effects of Picochlorum on shrimp culture, Picochlorum was added to the culture system of Litopenaeus vannamei at concentrations of 1×104cells/mL(KH_1), 2×104cells/mL(KH_2) and 4×104cells/mL(KH_4), and three culture systems with no Picochlorum addition were set up as control group(KH_D) . The water quality, diversity of microalgae community, growth performance and immune-related enzyme activities of shrimp were monitored in each treatment group. The results showed that, all three treatment groups with Picochlorum addition were effective in removing total ammonia nitrogen (TAN), nitrite, phosphate,and chemical oxygen demand (COD) from culture water compared to the control group. KH_4 had the best water purification effect among the three treatment groups. At the end of the experiment, TAN, nitrite, phosphate and COD contents of KH_4 were 0.75 mg/L, 1.41 mg/L, 0.76 mg/L, and 8.2 mg/L, respectively, which decreased by 89.85%, 78.17%, 50.00%, and 63.28%, respectively, compared to KH_D. High-throughput sequencing analysis showed that the absolute dominant genus in the microalgae communities of KH_1, KH_2 and KH_4 were all Picochlorum, with relative abundances of 70.03%, 71.69% and 95.65% respectively, and were significantly higher than that in KH_D (p<0.05). The absolute dominant microalgae in KH_D was Isochrysis (69.59%). The addition of Picochlorum had a significant impact on the microalgae community diversity structure in the shrimp farming system. The superoxide dismutase (SOD) activities of shrimp in KH_D,KH_1,KH_2 and KH_4 groups were 88.50 U/mg prot,116.58 U/mg prot,157.57 U/mg prot,152.23 U/mg prot,and the lysozyme (LZM) activities were 29.48 U/mg prot,34.47 U/mg prot,47.17 U/mg prot, 51.22 U/mg prot.The activities of both enzymes were increased by 31.73%-78.05% and 16.93%-73.74% in the experimental group of Litopenaeus vannamei (KH_1, KH_2, KH_4) compared to KH_D, respectively. The enzyme activities and growth performance of Litopenaeus vannamei in KH_2 and KH_4 were significantly better than that in KH_D (P < 0.05). In summary, the addition of Picochlorum can improve the shrimp culture water environment and promote shrimp growth, which is a feasible solution for shrimp aquaculture environmental control.