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%

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{per thousand}. 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, P0.05), 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{per thousand}, with an optimal inferred C:N range of 18.5-21.0:1 for water quality and growth performance.