PURPOSE: To provide a fish cultivation feed compounded with a specific polysaccharide, absorbable and digestible as a nutrient, having improved feed efficiency and effectively utilizable as an agent for the prevention and treatment of various fish diseases.

CONSTITUTION: This fish cultivation feed is produced by compounding a polysaccharide produced e.g. by Leuconostoc mesenteroides subsp. dextranicum BL-75 strain (FERIVI BP-2242) and having the following properties. Nature, tasteless and odorless white amorphous powder; solubility, soluble in water, formamide and dimethyl sulfoxide and insoluble in alcohol, acetone, benzene, ethyl acetate, hexane, chloroform and carbon tetrachloride; pH of aqueous solution, neutral to weakly acidic; constituent sugar, exclusively glucose; elemental analysis, C 43.0-45.0% and H 6.0-6.3%; structure, α-glucan containing α-1,6 bond as main bond; molecular weight, estimated as 210,000; color reactions, positive to anthrone-sulfuric acid reaction and phenol-sulfuric acid reaction and negative to biuret reaction; etc.