Effects of Mangrove (Avicennia marina) Leaf Aqueous Extract on Growth, Immunity, and Hypoxia Tolerance in Gray Mullet (Liza ramada)

Abstract

This study evaluates the influences of dietary mangrove (Avicennia marina) leaf aqueous extract (MLAE) on growth, health, and stress tolerance in Liza ramada over an 84-day feeding assessment. Fish (initial weight: 34.89 ± 0.15 g) were served diets encompassing 0, 100, 200, 300, or 400 mg/kg MLAE. The 300 mg/kg MLAE group reached the best growth performance compared to other groups (p < 0.05). The feed conversion ratio (FCR) was also the most productive at this level. Polynomial regression identified an optimal MLAE range of 250–275 mg/kg for maximizing growth and feed efficiency. Digestive enzyme potencies (amylase, lipase, and protease) were elevated (p < 0.05) in the 300 and 400 mg/kg groups. Higher MLAE levels reduced total bacterial count and populations of Vibrio spp. and Escherichia coli. Histological analysis showed enhanced intestinal villi structure and immune cell infiltration in MLAE-fed groups. Blood chemistry revealed increased total protein (TP), albumin (AB), and globulin contents and reduced cholesterol in the 200–400 mg/kg groups. MLAE improved hypoxia tolerance, indicated by increased LT50% values, and reduced stress markers (glucose, cortisol) under hypoxia. Immune indicators (lysozyme activity, bactericidal activity [BA], and NBT%) and antioxidant enzyme activities (superoxide dismutase [SOD], catalase [CAT], glutathione peroxidase [GPx]) were enhanced, with lower malondialdehyde (MDA) levels. These outcomes suggest that MLAE supplementation enhances growth, health, and stress resilience in gray mullets, offering potential applications for sustainable aquaculture. Further studies should explore the mechanistic pathways underlying these benefits and assess the long-term impacts of MLAE supplementation on fish health and aquaculture productivity.