Changes of cortisol hormone caused by stressing Rainbow Trout

Abstract

Chronic and acute effects of stress on the reproductive system and hormonal balance in higher vertebrates is well documented, but the subject is little investigated on fish. Understanding the courses of stress to eliminate or minimize them, will contribute to designing culture systems, or methods, based on the physiological requirements of fish. This will consequently enhance production of cultured fish. This study has investigated the effects of stress as a result of handling and induced spawning through injection of HCG (1100 IU/kg), GnRH (2 Ug/kg), dopamine antagonist (25 mg/kg) and distilled water (0.5 cc/kg). Taking into consideration that the secretion of cortisol is the first response to stress, therefor the level of cortisol in the blood of injected fish (rainbow trout spawners) was compared by using Radio Immuno-Assay technic. In three treatments cortisol level of blood after 10, 15, 20, 25, 30 and 35 minutes after stress was measured. The present study showed a significant increase in the level of cortisol in the blood of fish compared to uninjected control treatment. This increase was caused by stress related to handling and spawning. There were no highly significant difference (P < 0.01) in the cortisol level among the fish injected with HCG, GnRH and dopamine antagonist. The type of injecting material does not make a difference in the amount of stress and cortisol level. This research has concluded that handling and injection make a significant stress for the spawning fish. It is recommended to use ecological factors to persuade natural spawning without disturbance and injections.