Figure 4: (a) Electro-olfactogram (EOG) responses to waters from three streams in juvenile chum salmon during downstream migration. (b) Effects of oral thyroxine (T4) administration on the gene expression ratios of the N-methyl-D-aspartate receptor essential subunit NR1 in the whole brain of juvenile chum salmon.

(a) Juvenile fish were sampled at the Chitose Hatchery (Site A), the second bridge of the Chitose (Site B), the Chitose River in Kamaka Ward (Site C), the confluence point of the Chitose and Yubari Rivers (Site D), the mouth of the Ishikari River (Site E), and Ishikari Bay (Site F). The values are the means ± SEM of data obtained from three juvenile fish. Different letters represent significant differences using one-way ANOVA followed by the Dunnett test (p < 0.05). (b) Juvenile chum salmon reared in the Chitose Hatchery were transferred to the Toyohira Salmon Museum, fed pellets containing 2 mg/g T4 (Experimental fish) or pellets without T4 (Control fish), and sampled at days 0, 1, 4, 7, and 14 to evaluate NR1 expression. The gene expression levels of NR1 in the whole brain were normalized to the reference gene (β-actin), and the expression levels were compared using the relative Ct (ΔΔCT) method. Data are presented as the means ± SEM (N = 7–8). Different letters present significant differences using the Steel-Dwass test (p < 0.05).