Effects of carbon‐to‐nitrogen ratio (C:N) on water quality and growth performance of Litopenaeus vannamei (Boone, 1931) in the biofloc system with a salinity of 5‰

Abstract

This study aimed to investigate the effects of carbon-to-nitrogen ratio (C:N) on water quality and shrimp growth performance during the grow-out culture of Litopenaeus vannamei in a biofloc system under a low salinity condition. Three biofloc treatments with a C:N (contained in feed and exogenous carbon source with the assumption that 75% of the feed nitrogen is excreted) of 8:1 (CN8), 16:1 (CN16) and 24:1 (CN24), respectively, were designed to stocking shrimp juveniles (~0.8 g shrimp−1) at a density of 270 individuals m−3, for a 63-day culture experiment at a salinity of about 5‰. Water parameters were monitored, and zootechnical indices were determined in the three treatments. Results showed that in CN8 treatment, pH, carbonate alkalinity, biofloc volume and TSS were significantly lower (p < 0.05), whereas TAN, nitrite and nitrate were significantly higher, than those in the other two treatments (p < 0.05). The zootechnical parameters of shrimp were not significantly different among the three treatments (p > 0.05), except that the survival rates in CN16 treatment (96.8 ± 2.0%) and CN24 treatment (93.7 ± 4.2%) were significantly higher than that of CN8 treatment (81.5 ± 6.4%, p < 0.05). Regression analysis revealed that the optimal C:N range for pH, SVI (sludge volume index), TAN, nitrate and survival rate was 20.5:1, 18.5:1, 21.0:1, 20.8:1 and 18.6:1. The results suggested that the C:N higher than 16 were suitable for culturing L. vannamei in the biofloc system with a salinity of 5‰, with an optimal range of 18.5–21.0:1.