Spathoteredo obtusa Ethanol Extract as an Immunostimulant Against Vibrio parahaemolyticus in Pacific Whiteleg Shrimp

Vibrio parahaemolyticus-induced AHPND threatens global Litopenaeus vannamei aquaculture. This study pioneers the use of Spathoteredo obtusa ethanol extract, an underutilized mangrove resource, as a sustainable immunostimulant. The extract (300, 400, 500, 600, and 700 mg/L) was coated onto feed and administered for 14 days prior to challenge. Immune parameters (THC, DHC, phagocytosis, and respiratory burst) were quantified following Vibrio parahaemolyticus exposure. Bioactive compounds were profiled via LC-HRMS. The optimal 600 mg/L treatment significantly increased THC (44.0 ± 1.2 × 10⁵ cells/mL; +39.7%), phagocytosis (59.0 ± 2.57%), and respiratory burst (0.746 ± 0.004 OD₆₃₀) compared to infected controls. Hyaline cells rose to 56%, accompanied by an increase in granular cells. Spathoteredo obtusa extract at 600 mg/L enhances shrimp immunity against vibriosis, demonstrating potential for use in functional aquafeeds. Field validation is recommended prior to commercial adoption.