title: Changes in the plasma levels of insulin-like growth factor-I from the onset of spawning migration through upstream migration in chum salmon.
abstract: An increase in activity of the pituitary-gonadal axis (PG-axis) and gonadal development are essential for the onset of spawning migration of chum salmon from the Bering Sea. In the Bering Sea, fish with larger body sizes initiated gonadal development and commenced spawning migration to the natal river by the end of summer. We thus hypothesized that insulin-like growth factor-I (IGF-I), a somatotropic signal that interacts with the PG-axis, can be one of such factors responsible for the onset of migration, and examined changes in plasma levels and hepatic expression of IGF-I gene in oceanic and homing chum salmon in 2001-2003. The plasma IGF-I levels and corresponding body sizes in maturing adults, which had developing gonads, were significantly higher than those in immature fish in all years examined. Such increase in the plasma IGF-I levels in maturing fish was observed even in the Gulf of Alaska during February 2006, while coincident increase was not observed in the hepatic amounts of IGF-I mRNA. In autumn, the plasma IGF-I levels in homing adults decreased during upstream migration in the Ishikari River-Ishikari bay water system in Hokkaido, Japan. In conclusion, the plasma IGF-I levels increased with gonadal development when chum salmon migrated from the winter Gulf of Alaska to the summer Bering Sea. Circulating IGF-I may interact with the PG-axis and promote gonadal development that is inseparable from the onset of spawning migration. Circulating IGF-I levels were thereafter lowered in accordance with final maturation during upstream migration in the breeding season.
authors: Graduate School of Bioresource and Bioenvironmental Sciences, Kyushu University, Fukuoka 812-8581, Japan. takeshikiai@msn.com
authors: Takeshi A
authors: TA
authors: Onuma
authors: Keita
authors: K
authors: Makino
authors: Hiroshi
authors: H
authors: Katsumata
authors: Brian R
authors: BR
authors: Beckman
authors: Masatoshi
authors: M
authors: Ban
authors: Hironori
authors: H
authors: Ando
authors: Masa-aki
authors: MA
authors: Fukuwaka
authors: Tomonori
authors: T
authors: Azumaya
authors: Penny
authors: P
authors: Swanson
authors: Akihisa
authors: A
authors: Urano
mesh_terms: D025041:Animal Migration / Q000502:physiology*; D000818:Animals; D049628:Body Size; D006066:Gonads / Q000378:metabolism; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000378:metabolism*; D008297:Male; D017685:Oncorhynchus keta / Q000097:blood* / Q000502:physiology*; D016133:Polymerase Chain Reaction; D011863:Radioimmunoassay; D012098:Reproduction / Q000502:physiology*; D012726:Sexual Behavior, Animal / Q000502:physiology
chemical_list: D007334:Insulin-Like Growth Factor I