The GH/IGF-I axis plays an essential role in the regulation of
growth in fish (Moriyama et al., 2000). GH acts directly on target
organs by stimulating mitosis and affecting various aspects of energy
metabolism in teleosts (Wood et al., 2005). Many of the actions of
GH are mediated through its stimulation of the expression and release
of IGF-I in the liver. IGF-I is also produced in various tissues in
teleosts where it presumably acts in an autocrine or paracrine fashion
(Duan, 1997). Thus, it might be expected that the development of
hypoosmoregulatory ability of chum fry refrains through the rearing
in freshwater hatcheries for prolonged periods due to repression of
the GH/IGF-I axis. It may negatively affect the most fast-growing stage
in their life span. We examined the growth of chum salmon fry while
maintaining the fry for several weeks in freshwater and seawater. The
objective of this study was therefore to examine growth and physiological
variables associated with seawater adaptability and growth,
as well as the major endocrine regulators of these processes in chum
salmon fry while maintaining the fry for several weeks in freshwater
and seawater.