Effects of methanolic mealworm extract on zebrafish: growth, immunity, and gene expression

This study evaluated the effects of methanolic mealworm extract (MME) dietary supplementation on growth performance, immunity, biochemical markers, histomorphology, antioxidant status, and gene expression in zebrafish (Danio rerio). Four groups were fed diets containing 0% (MME0, control), 0.25% (MME1), 0.5% (MME2), and 1% (MME3) MME for 8 weeks. Growth performance improved significantly in a dose-dependent manner, with the MME3 group showing the highest weight gain (+ 80%, p < 0.05), feed efficiency, and survival rate. MME2 and MME3 significantly increased mucosal immune parameters, including total protein, lysozyme, and alkaline phosphatase (ALP) activity (p < 0.05). The levels of total protein, immunoglobulin, and lysozyme in the serum also increased significantly in the MME2 and MME3 groups. Glucose levels decreased in a dose-dependent manner (p < 0.05), whereas cholesterol, albumin, triglycerides, and LDH levels remained unchanged (p > 0.05). Histological analysis of the intestinal tissue revealed significantly greater villus height in the MME2 group and villus diameter in the MME3 group (p < 0.05), with no significant differences in the other groups (p > 0.05). Antioxidant enzyme activities (SOD and CAT) and their gene expression did not differ significantly among groups (p > 0.05). Liver enzyme analysis revealed increased ALP levels in the MME2 and MME3 groups (p < 0.05), whereas ALT and AST levels remained unchanged (p > 0.05). Methanolic mealworm extract significantly increased the expression of immune-related genes in zebrafish (p < 0.05). The highest LYZ expression was observed in the MME3 group (3.92-fold), with no difference between MME1 and MME2 (p > 0.05). TNF levels were highest in MME2 (4.51-fold) and MME3 (5.50-fold). IL-1β expression showed a dose-dependent increase, with the MME3 group (3.91-fold) displaying the highest level (p < 0.05). Growth-related genes, including GH, IGF, and appetite-related GHRL, were significantly elevated in the MME2 and MME3 groups (p < 0.05). In conclusion, MME, particularly at 1%, significantly enhanced zebrafish growth, immunity, and gene expression, suggesting its potential for broader aquaculture applications after being tested in other fish models.