A fish growth hormone provided by a purified extract obtained from the pituitary gland of a fish belonging to salmonoid; the hormone is a polypeptide having the following physicochemical properties:
(I) amino acid composition: as indicated in table 1; (II) the sequences of 33 amino acids at the N-terminal and 23 amino acids at the C-terminal are as follows:
N-terminal: H 2 N-Ile-Glu-Asn-Gln-Arg-Leu-Phe-Asn-Ile-Ala-Val-Ser-Arg-Val-Gln-His-Leu-His-Leu-Leu-Ala-Gln-Lys-Met-Phe-Asn-Asp-Phe-Asp-Gly-Thr-Leu-Leu-C-terminal: -Met-His.Lys-Val-Glu-Thr-Tyr-Leu-Thr-Val-Ala-Lys-Cys-Arg-Lys-Ser-Leu-Glu-Ala-Asn-Cys-Thr-Leu-OH; (III) molecular weight: about 22,000; (IV) isoelectric point: 5.6-5.7; and (V) soluble in an alkaline aqueous solution and hardly soluble or insoluble in neutral and acidic aqueous solutions.