Dietary administration of polyethylene glycol-formulated tyramine enhances immunity and disease resistance in Litopenaeus vannamei.

This study evaluated whether polyethylene glycol (PEG) formulation could prolong the biological efficacy of dietary tyramine (TA) and provide sustained oral immunostimulation in Litopenaeus vannamei by examining growth performance, immune responses, disease resistance, and biogenic amine regulation during a 120-day feeding trial. Shrimp were assigned to four dietary treatments: basal diet (BD), TA, PEG, and TA + PEG. Results showed that TA significantly enhanced growth performance, exhibiting higher weight gain than all other treatment groups at 56 days and improved feed efficiency at 56 and 120 days. At 120 days, both TA and TA + PEG groups showed significantly greater weight gain than the BD group. Immune analyses revealed that TA induced rapid activation of hemocyte parameters, phenoloxidase activity, and respiratory burst during the early feeding period (7-28 days), whereas TA + PEG maintained elevated immune responses at later stages (56-120 days), indicating prolonged immunostimulation. In disease challenge tests against Vibrio alginolyticus, both TA and TA + PEG improved survival at 28 days, but only TA + PEG maintained significantly higher survival at 56 days compared with all other groups, demonstrating superior long-term protection. Biogenic amine analysis showed that TA-fed shrimp had significantly lower tyramine levels than the BD group at 28 days, whereas the TA + PEG group exhibited significantly higher tyramine levels than the BD group, while octopamine levels were consistently elevated in both TA and TA + PEG groups at 28 and 56 days. Overall, PEG formulation prolonged the oral biological efficacy of dietary tyramine, resulting in sustained immune activation and enhanced disease resistance against to V. alginolyticus.