NMFS 70 November 1988 New and Innovative Advances in Biology / Engineering with Potential for Use in Aquaculture

Two molecular forms of salmon growth hormone, GH I and II, have been isolated from the pituitary glands of the chum salmon, Oncorhynchus keta. A two-step procedure was employed for extraction of the salmon GHs under an alkaline (pH 9-10) condition, subsequent to acid acetone extraction. The GHs were then purified by isoelectric precipitation at pH 5.6, gel filtration on Sephadex G 100, and high-performance liquid chromatography on ODS. A molecular weight of 22,000 was estimated for both forms of salmon GH by gel electrophoresis in sodium dodecyl sulfate. Isoelectric points, by gel electrofocusing, of 5.6 and 6.0 were estimated for salmon GH I and II, respectively, with differences present in the amino acid composition and the N-terminal residue, suggesting that they may be genetic variants coded on two separate genes. The partial amino acid sequence of salmon GH I at both terminal regions has been determined. Intraperitoneal injection of salmon GH I at doses of 0.01 Jig and 0.1 Jig/g body weight resulted in a significant increase in body weight and length ofjuvenile rainbow trout. The growthpromoting effect lasted longer even after cessation of GH treatment. The long-lasting effect of GH treatment was also induced by a single injection at higher doses of 5 to 50 Jig/fish (30 g body weight). Growth hormone (GH) stimulates animal growth throughout the vertebrates. In view of the potential applications in fish culture, interest is increasing in the study of fish pituitary hormone in general, and the growth hormone in particular. However, until recently chemical knowledge of GH has been mainly confined to mammals, although many attempts have been made to purify these hormones in lower vertebrates such as shark (Lewis et al. 1972), tilapia (Farmer et al. 1976), salmon (Higgs et al. 1978; Komourdjian and Idler 1979, Wagner et al. 1985), sturgeon (Farmer et al. 1981), and carp (Cook et al. 1983). Our recent studies on the isolation and characterization of chum salmon GH (Kawauchi et al. 1986a) and the gene cloning (Sekine et al. 1985) will promote a better understanding of fish physiology and application to fish culture. The present paper describes isolation and characterization of two genetic variants of chum salmon GHs (I and II) and examines effects of salmon GH on growth of juvenile rainbow trout. Materials and methods _