Migration tendency in juvenile steelhead trout, Salmo gairdneri Richardson, injected with thyroxine and thiourea |
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| Authors: | E K Birks R D Ewing A R Hemmingsen |
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| Institution: | Corvallis Fish Research Laboratory, 303 Extension Hall, Oregon State University, Corvallis, Oregon 97331, U.S.A. |
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| Abstract: | Juvenile steelhead trout, Salmo gairdneri injected with thyroxine (T4) near the time of seaward migration exhibited a significantly lower migration tendency than untreated controls of fish injected with saline, thiourea, or a combination of T4 and thiourea. Fish injected with thiourea alone or in combination with T4 prior to the time of maximum migration tendency showed enhanced migration over untreated and saline injected controls and those injected with T4 alone. Injections of T4 or a combination of T4 and thiourea elevated plasma T4 and tri-iodothyronine (T3) concentrations, while injection of thiourea alone depressed thyroid hormone levels relative to saline-injected controls. Plasma concentrations of T3 and T4 returned to control levels within 10 days in all groups. We suggest that thyroid hormones are antagonistic to mechanisms underlying seaward migration of steelhead trout and that these antagonistic effects must be overcome before migration tendency is expressed. |
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