Laserfiche WebLink
36 <br />The temperature graphs (Figs. 6-15) indicate narrower ranges of <br />fish and water temperatures in July and August, when squawfish move into <br />main channel habitats. Minor variations in temperature are very important <br />to spawning of the northern squawfish, a congener of the Colorado <br />squawfish (Beamesdefer and Congleton, 1981). Spawning began, in the St. <br />Joe River, Idaho, when water temperatures reached 140C. Spawning stopped, <br />abruptly, when a cold rain caused water temperatures to fall below WC <br />and resumed when the water temperature returned to 14°C and above. This <br />observation, in conjunction with others (Jeppson and Platts, 1959; Hill, <br />1962), supports the hypothesis that specific temperature requirements <br />are needed by Colorado squawfish for spawning. <br />Temperature and photoperiod influence fish behavior and physiology <br />in several ways (Magnuson et al., 1979). The interaction of these two <br />environmental stimuli triggers gonadal maturation, which ensures that fish <br />will spawn during periods when environmental conditions are most favorable <br />(Schwassmann, 1971). <br />This environmental influence is hypothesized to occur in two stages. <br />In the initial stage, physical stimuli act through the "brain-pituitary- <br />gonad axis" to release hormones, which initate gonadal maturation. This <br />is a relatively slow metabolic process that is activated by cumulative <br />exposure to environmental changes. The second stage, triggered by the <br />occurrence of the first stage and additional environmental changes, is <br />final maturation of the gonads; this may occur relatively fast compared <br />with the first stage (Liley, 1969). <br />One possible explanation for several adult-size squawfish not <br />migrating may be related to inadequate stimuli to trigger the initial <br />process of gonadal maturation. Our data indicate that this triggering