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 the water quality and shrimp growth performance during the grow-out culture of Litopenaeus vannamei in the biofloc system under a low salinity condition. Three biofloc treatments with an C:N (contained in the inputted feed and 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) at a density of 270 individuals m^-3, for a 63-days culture experiment at a salinity of about 5‰. Results showed that in CN8 treatment, the levels of pH (6.9±0.1), carbonate alkalinity (104.0±2.8mg L^-1 CaCO₃), biofloc volume (4.8±0.9mL L^-1) and TSS (327.4±24.4mg L^-1) were significantly lower than those in the other two treatments (≥7.6±0.3, ≥157.6±21.6mg L^-1 CaCO₃, ≥24.1±3.7mL L^-1 and ≥508.1±32.3mg L^-1, P<0.05); whereas the levels of TAN (7.1±0.9mg L^-1), nitrite (14.0±3.6mg L^-1) and nitrate (77.0±5.0mg L^-1) were significantly higher than those in the other treatments (≤2.0±0.6mg L^-1, ≤4.9±3.1mg L^-1 and ≤14.7±5.9mg L^-1, P<0.05). The zootechnical parameters of shrimp were not significantly different between 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). The results indicated that an inputted C:N higher than 16:1 was suitable for the biofloc system with a low salinity of 5‰, with an optimal inferred C:N range of 18.5-21.0:1 for water quality and growth performance.