To develop and provide a disease-resistant method for fry of marine fish affording consumers with sense of security by stabilizing fry production and reducing chemical agents used.

The disease-resistant method for fry of marine fish comprises the following practice: in rearing the fry by an artificial fry-raising method, rearing water is subjected to low-saline treatment by adding fresh water, the resultant low-saline condition is maintained for a given period, and the fry thus raised is returned to the whole seawater; that is, in rearing the fry by an artificial fry-raising method, rearing water is subjected to diluted seawater treatment(low-saline treatment), and after the lapse of a given period, the fry thus raised is returned to the whole seawater.