Transcriptional response of immune-related genes in Litopenaeus vannamei post-larvae cultured in recirculating aquaculture systems with and without biofloc

In the present study, quantitative real-time RT-PCR was used to monitor the transcriptional responses of seven key genes related to some innate immune pathways in shrimp postlarvae after being placed in a recirculating aquaculture system (RAS) with or without biofloc (BF or no-BF). Each system consisted of the main tank with 400 L of seawater and six glass aquariums (50 L each). Besides, the nucleotide sequences of myosin light chain (LvMyo) from Litopenaeus vannamei related to the phagocytosis pathway were described. The sequence analysis indicated that LvMyo is a conserved protein among crustaceans and is present in other arthropods. The transcriptional response to the treatments showed several expression patterns. The prophenoloxidase gene was up-regulated in both systems (P < 0.05) and was higher in BF than in no-BF (P < 0.01). Phagocytosis-related genes depicted differential expressions. LvMyo, Ras-associated binding 6, and Ras-related nuclear protein expressions were higher in BF than in no-BF (P < 0.05). Regarding antioxidant genes, glutathione peroxidase was up-regulated only in BF (P < 0.05). Superoxide dismutase expression was lower in BF at 12 h (P < 0.05), but higher at 24 h (P < 0.05). These findings suggest that biofloc modulates the transcription of genes related to the immune response in shrimp as an early response or at the mid-term. Besides, the biological filter in a RAS without biofloc seems to be able to maintain a bacterial population that promotes a lower but similar response to that induced in the biofloc system.