Effects of different carbon sources and dietary protein levels in a biofloc system on growth performance, immune response against white spot syndrome virus infection and cathepsin L gene expression of Litopenaeus vannamei

A 5-week study was performed to evaluate the effect of spoilage date extract (SDE) as the biofloc carbon source on Litopenaeus vannamei (5.4 +/- 0.3 g) performance. The two levels of dietary protein (15% and 25% crude protein) and two carbohydrate sources (molasses-M and SDE-P) were tested including: M15, M25, P15 and P25. The minimum (0.2 +/- 0.0 mg/L) and the maximum (0.5 +/- 0.0 mg/L) of total ammonia nitrogen were observed in the P15 and M25 groups respectively. The highest protein efficiency ratio (6.1 +/- 0.3) and protein productive value (112.3 +/- 5.8%) were found in the P15 group (p < 0.05). No significant difference was found between biofloc treatments in the expression of cathepsin L gene in hepatopancreas (p > 0.05). The number of total haemocyte count (THC), semigranular cells (SGC) and granular cells (GC) of shrimp in SDE-based biofloc treatments was relatively higher than those in molasses-based biofloc treatments. Following the white spot syndrome virus (WSSV) challenge, a significant decrease in THC, SGC, GC and hyaline cell values was observed in all treatments (p = 0.001). Plasma biochemical parameters were significantly influenced by dietary protein levels, biofloc carbon sources as well as WSSV challenge test. In conclusion, SDE successfully could be used as an alternative carbon source for establishing a biofloc system in L. vannamei production.