The immune defense response of Pacific white shrimp (Litopenaeus vannamei) to temperature fluctuation.

Temperature is a significant environmental factor contributing to the success of aquaculture. To investigate the immune defense response during temperature fluctuation, Litopenaeus vannamei (L. vannamei) was treated under conditions of gradual cooling from an acclimation temperature of 28 °C (C group) to 13 °C (T group) in 2 days with a cooling rate of 7.5 °C/d and then rewarmed to 28 °C (R group) using the same rate. Relative expression of immune defense system-related genes and intestinal microbial composition in L. vannamei were investigated. The results showed that with a decrease in temperature, the expression of TLR, IMD, proPO and Casp3 in intestine was significantly decreased, while the expression of Muc-3A, Muc-5AC, Muc-17, IAP, p53, HSP70, MT and Fer was significantly increased after cooling. After temperature recovery, gene expression generally showed a trend of recovering to the normal level (C). Intestinal microbial analysis showed that, compared with the C group, the Chao and Ace indexes, the relative abundance of microflora from the Phylum Bacteroidetes, Class Alphaproteobacteria, and Class Bacteroidia, significantly decreased in the R group. The results revealed that cold-stress may decrease microbial community richness, alter the bacterial community in general and reduce shrimp immunity to pathogens and antibacterial activity. As a result, during temperature fluctuation shrimp may mobilize the immune defense system through upregulating the expression of Muc genes, anti-apoptosis related genes, and antioxidant related genes in order to maintain organism homeostasis as well as to repair damaged intestinal tissue.