Combined effects of glutamine dipeptide, plant essential oils, and Astragalus polysaccharide on growth performance, antioxidant capacity, immune function, and intestinal health in large yellow croaker (Larimichthys crocea)

As the most productive fish species in marine aquaculture in China, large yellow croaker ( Larimichthys crocea ) farming faces dual challenges: the frequent outbreak of diseases and increasing environmental pressures. While high-dose antibiotic treatments may offer short-term disease control, they contribute significantly to the development of drug resistance. Consequently, the development of eco-friendly and safe immune enhancers, along with the implementation of nutritional intervention strategies, has become a focal point of current research. This study investigated the combined effects of dietary supplementation with glutamine dipeptide (GLN), plant essential oil (PEO), and Astragalus polysaccharide (APS) on growth performance, antioxidant capacity, immune function, and gut microbiota of L. crocea . A 60-day feeding trial was conducted in sea cages with four dietary groups: control (basal diet), GLN (2 %), GLN+PEO (2 % GLN + 0.55 % PEO), and PEO+APS (0.55 % PEO + 0.1 % APS). Results indicated that GLN+PEO significantly improved the survival rate and enhanced liver antioxidant enzyme activities (CAT, GSH-PX, T-AOC) ( P < 0.05). PEO+APS showed the strongest systemic antioxidant effect, reducing lipid peroxidation in serum and intestine while elevating lysozyme activity ( P < 0.05). GLN alone protected against hepatic oxidative damage but had limited growth-promoting effects. Gut microbiota analysis revealed distinct restructuring, with PEO+APS maintaining higher microbial diversity and enriching beneficial genera ( Faecalibacterium , Bifidobacterium ), while GLN+PEO reduced microbial richness. These findings demonstrate that combinatorial additives (especially PEO+APS combination) offer superior benefits for enhancing health and stress resistance in intensive aquaculture, providing a sustainable alternative to antibiotics. • The combination of plant essential oils (PEO) and Astragalus polysaccharide (APS) significantly enhanced systemic antioxidant capacity, reducing MDA in serum and intestine in large yellow croaker. • GLN+PEO enhances the activity of amylase in the gastrointestinal tract and AKP in the hindgut. • The PEO+APS combination triggered the strongest immune response, elevating serum lysozyme activity, which support intestinal health and pathogen defense.