Polyethylene glycol-formulated tyramine prolongs selected innate immune activation and enhances disease resistance in giant river prawn Macrobrachium rosenbergii

Objective This study evaluated whether polyethylene glycol-formulated tyramine (PEG-TA) could prolong selected immunological responses and enhance disease resistance in giant river prawn Macrobrachium rosenbergii, a crustacean of significant economic importance. Methods In the present study, we employed the injection method to determine the effect of PEG-TA on giant river prawn. Each prawn was injected with 20 μL of saline (control), polyethylene glycol (PEG; 17.147 mg/L), tyramine (3.429 mg/L; 0.5 nmol/prawn), or PEG-TA containing 3.429 mg/L tyramine and 17.147 mg/L PEG (tyramine : PEG = 1:5, weight/weight). Immunological responses were subsequently assessed at 0, 0.5, 1, 2, 4, and 16 h postinjection. Results The results of the present study demonstrated a notable enhancement and prolongation of immune efficacy, as evidenced by significant increases in total hemocyte count, differential hemocyte count, lysozyme activity, phagocytic activity, and the survival rate in the challenge test against Lactococcus garvieae. Conclusions The PEG-TA prolonged selected immunological responses and enhanced resistance to L. garvieae relative to free tyramine. These findings demonstrate prolonged biological effects of the formulation.