Dietary prebiotic-stevioside modulates the growth, antioxidant enzymes, and immune response in thinlip mullets (Liza ramada) subjected to chronic cold stress.

Plant active ingredients, including stevioside, with their prebiotic properties and antioxidant potential, hold promise as innovative components in aquaculture. This study assessed the multi-level impacts of stevioside (0, 100, 200, 300, 400, or 500 mg/kg) on thinlip mullet (N = 540 juveniles with an initial weight 3.50 ± 0.07 g) exposed to a long-term low temperature regime (18 °C) for 60 days. Growth, blood parameters, enzymes, immune genes, and histological structure of intestine and liver were analyzed. Moderate stevioside doses (300-500 mg/kg) significantly boosted growth, with 400 and 500 mg/kg groups showing the highest final and daily weight gain. These doses also increased total protein in blood serum. Interestingly, stevioside did not affect key blood markers like albumin, triglycerides, liver enzymes (ALT and AST), urea, or creatinine. However, it markedly enhanced (P < 0.05) antioxidant enzyme activity in liver (SOD, CAT, GPx) of experimental groups compared to the control group. Gene expression analysis in liver tissue revealed notable effects. Lower stevioside doses (100-300 mg/kg) downregulated genes linked to inflammation (IL-1β) and iron regulation (hepcidin), while higher doses (400-500 mg/kg) showed dose-dependent upregulation (P < 0.05). Histological studies confirmed improved intestinal villi structure and absorptive area in the 300-500 mg/kg groups. This valuable information paves the way for sustainable aquaculture practices utilizing stevioside as a functional ingredient. This study provides key insights into the multi-level responses of juvenile mullets to dietary stevioside, with potential implications for aquatic animals exposed to similar circumstances.