Figure 6: Electro-olfactogram (EOG) responses to waters from three streams in adult male chum salmon collected at the Indian Waterwheel (a), and effects of GnRH analogue implantation on the EOG response to three stream waters in adult male chum salmon collected from Ishikari Bay (b,c).

(a) Adult fish were collected at the Indian Waterwheel (Site H). The relative EOG responses to the Ishikari River water, Chitose River water, and Toyohira River water are expressed as a proportion of the mean response to 0.1 mM L-Serine dissolved in distilled water. The values are means ± SEM of data obtained from seven adult fish. Different letters represent significant differences using one way ANOVA followed by the Dunnett test (p < 0.05). (b) Adult chum salmon including strays from another hatchery and (c) adult chum salmon originating from the Chitose Hatchery (confirmed by the otolith thermal marks) caught in Ishikari Bay (Site F) prior to entering to the river were reared in seawater at 13 °C using a refrigerator truck, implanted with either 300 μg (GnRH 24 h, 48 h) or 0 μg (Control 48 h) of GnRHa, and sampled at 0 (Initial control), 24, and 48 h. The relative EOG responses to the Ishikari River water, Chitose River water, and Toyohira River water are expressed as a proportion of the mean response to 0.1 mM L-serine dissolved in distilled water. Data are presented as the means ± SEM (N = 4–5). Different letters represent significant differences using two-way ANOVA followed by the Tukey-Kramer multiple comparison test (p < 0.05).