Tyramine injection enhances immune function and disease resistance in Penaeus monodon

The effects of tyramine (TA) on survival rates, immune parameters, carbohydrate metabolism, phenoloxidase (PO)-related gene expression, and haemocyte degranulation in Penaeus monodon were evaluated. Shrimp were injected with 100 pmol shrimp^-1 (TA100) or 1000 pmol shrimp^-1 (TA1000), and their responses were assessed over an 8 h period. Haemocyte degranulation was induced by co-culturing with 10^-4 M tyramine (TA) for 15-60 min. The expression of PO-related genes was significantly upregulated 1 h after injection with TA100 and TA1000. Additionally, immune parameters in shrimp including total haemocyte count (THC) at 0.5-2 h, hyaline cells (HCs) at 0.5-1 h, granular cells (GCs) at 0.5-1 h, semigranular cells (SGCs) at 0.5-2 h, phenoloxidase (PO) activity at 0.5-1 h with TA100 and at 2 h with TA1000, respiratory bursts (RBs) at 1 h, and both phagocytic activity and clearance efficiency against Photobacterium damselae at 0.5-1 h after TA100 and TA1000 injection, were all significantly enhanced. Moreover, shrimp treated with TA1000 exhibited significantly higher survival rates at 168 h post-challenge compared to the control group. Additionally, haemolymph glucose levels were reduced 2-4 h after injection with TA100 and TA1000, and lactate levels decreased 1 h after injection with TA1000. These results suggest that TA at doses of 100 and 1000 μg shrimp^-1 enhances immune responses (0.5-2 h) in P. monodon, thereby improving disease resistance against Pho. damselae.