Changes in Chum Salmon Plasma Levels of Steroid Hormones during Onset of the Spawning Migration in the Bering Sea

• Main Authors: Takeshi Onuma, Shunpei Sato, Aya Jodo, Nancy D. Davis, Hironori Ando, Masatoshi Ban, Masa-aki Fukuwaka, Akihisa Urano
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Migration; chum salmon; Bering Sea; maturation; testosterone; 11-ketotestosterone; estradiol-17β; HPG-axis; Pacific
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.541.4029; http://www.npafc.org/new/publications/Technical Report/TR6/page 104-106(Onuma).pdf

After a few years of oceanic life, Japanese chum salmon migrate to their natal rivers from the Bering Sea. Previous studies have demonstrated involvement of the brain-pituitary-gonadal (HPG) axis in regulation of the spawning migration. In homing chum salmon, expression of genes encoding salmon gonadotropin-releasing hormone (GnRH) was elevated in the forebrain during upstream migration from the coast to the natal hatchery (Onuma et al. 2004, in press). In the pituitary, amounts of mRNA encoding gonadotropin (GTH) IIβ and somatolactin were elevated in stocks migrating a long river (Kitahashi et al. 1998; Taniyama et al. 1999) and a short river upstream (Onuma et al. 2003b). Plasma levels of testosterone (T), 11-ketotestosterone (11KT) and estradiol-17β (E2) decreased along with final gonadal maturation, while those of 17α-20β-dihydroxy-4-pregnen-3-one (DHP) and cortisol elevated at the final phases of the spawning migration (Onuma et al. 2003a, b). Plasma levels of sex steroid hormones of chum salmon in the North Pacific Ocean were lower when compared to those of pre-spawning fish (Ueda et al., 1984; Ueda 1998). In farmed masu salmon, plasma levels of T, 11KT and E2 elevated with gonadal maturation from June through August (Munakata et al. 2001; Kitahashi et al. 2004). These results suggest involvement of the HPG-axis in initiation of the spawning migration in the Bering Sea.