Immunosuppression and immunomodulation of white shrimp at low salinity and under starvation

Abstract

Survival, immune parameters, resistance against Vibrio alginolyticus, and gene expressions of white shrimp Litopenaeus vannamei juveniles which had been reared at different salinity levels were examined. The survival rates of shrimp reared at 2.5‰ and 5‰ were significantly lower than those of shrimp reared at 15‰, 25‰, and 35‰. Shrimp reared at lower salinity levels showed lower hyaline cells (HCs), granular cells (GCs, including semi-granular cells), total haemocyte count (THC), phenoloxidase (PO) activity, respiratory bursts (RBs), superoxide dismutase (SOD) activity, and lysozyme activity, and showed decreased resistance against V. alginolyticus, but showed higher expressions of lipopolysaccharide and β-glucan-binding protein (LGBP), peroxinectin (PX), integrin β, prophenoloxidase (proPO), and α2-macroglobulin (α2-M), and other immune genes related to superoxide dismutase (SOD), and antimicrobial peptide. In another experiment, survival, immune parameters, resistance against V. alginolyticus, and gene expressions were examined in shrimp which had been denied food (starved) for 0∼14 days. HCs, GCs, THC, PO activity, RBs, and SOD activity significantly decreased in shrimp which had been starved for 1∼14 days. Mortality of 7-day-starved shrimp was higher than that of control shrimp against V. alginolyticus. The expression of integrin β significantly decreased after 0.5∼5 days of starvation, whereas expressions of LGBP, PX, proPO I, proPO II, prophenoloxidase activating enzyme (ppA), and α2-M increased after 0.5∼1 days. Immune parameters of shrimp which had been starved for 7 and 14 days and then received normal feeding were examined after 1∼5 days. All immune parameters of 7-day-starved shrimp were able to return to their baseline values after 5 days of re-feeding, whereas all parameters of 14-day-starved shrimp failed to return to the baseline values even with 5 days of re-feeding. Shrimp cultured at low salinity and shrimp deprived of food exhibited immunosuppression.