Water quality, shrimp growth performance and bacterial community in a reusing-water biofloc system for nursery of Penaeus vananmei rearing under a low salinity condition

Abstract

This study aimed to investigate water quality, growth performance of Penaeus vananmei postlarvae (PL) and bacterial community in a reusing-water biofloc system under a low salinity condition. PLs (~ stage 15) were stocked in two biofloc systems: the reusing-water system (RS) and the new-water system (NS), at a density of 4000 individuals m−3 for a 28-days nursery experiment at a salinity of 5.0‰, with a C:N of 15:1. Results showed an acceptable growth performance of shrimp in RS that the final body weight and productivity were 0.104 ± 0.014 g shrimp−1 and 0.37 ± 0.05 kg m−3, although those parameters were significantly lower than those in NS (0.138 ± 0.018 g shrimp−1 and 0.48 ± 0.07 kg m−3, P < 0.05). However, the survival rate of shrimp in RS (88.9 ± 4.2%) was not significantly different from that of NS (86.6 ± 6.5%, P = 0.786). The TAN and nitrite levels in RS were 1.90 ± 0.42 and 6.55 ± 0.86 mg L−1, non-significantly higher than those in NS (0.04 ± 0.02 and 0.07 ± 0.01 mg L−1, P ≥ 0.05). Whereas, the levels of total nitrogen (285.5 ± 10.2 mg L−1) and nitrate (24.8 ± 2.7 mg L−1) in RS were significantly higher than those in NS (231.3 ± 6.1 and 4.6 ± 0.4 mg L−1, P < 0.05). The Shannon index of bacterial community in RS (6.22 ± 0.02) was significantly lower than that in NS (7.23 ± 0.02, P < 0.05). The bacterial communities in both systems were dominated by Bacteroidetes (10.64–15.55%), Firmicutes (4.11–9.42%), Planctomycetes (14.43–29.67%) and Proteobacteria (38.73–50.35%) with few ammonia- and nitrite-oxidizing bacteria. The proportions of denitrification bacteria and heterotrophic nitrification-aerobic denitrification bacteria in RS were 0.65 ± 0.07% and 5.73 ± 0.23%, significantly lower than those in NS (9.05 ± 0.15% and 9.26 ± 0.14%, P < 0.05). The results suggested that acceptable growth performance of postlarvae and water quality could be obtained in the reusing-water biofloc system, although the nitrogenous load was slightly high and should be studied next to reduce.