Enhancer for improving immunity of aquatic animals, preparation method thereof, and application of enhancer in feed

The invention discloses an enhancer for improving the immunity of aquatic animals. The enhancer comprises 15-20 g/L of a concentrated molasses fermentation liquor, 4-8 g/L of melatonin, 15-20 g/L of sodium alginate, 5-8 g/L of a nitrogen source, 3-5 g/L of a phosphorus source, 1-2 g/L of a potassium source, 3-5 g/L of high-activity humic acid and 10-15 [mu]g/L of selenium methionine. The inventionfurther discloses a preparation method and an application of the enhancer. The enhancer has the characteristics of treatment of both symptoms and root causes, safety, no toxicity, no drug resistance,no pollution, no residue and the like, and has the effects of inhibiting bacteria, resisting bacteria, improving the immunity of aquatic animals, resisting bacteria, preventing and controlling parasites, and resisting viruses; and the enhancer is suitable for aquatic animals in various growth stages, and particularly can solve the problem that the immunity of bred animals is reduced due to induction of high-temperature se