コイの低温・空気露呈耐性に及ぼす予備冷却の効果〔英文〕

概要

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Strengthening the tolerance to cold air exposure, an important subject in the waterless transportation of live fish, was attempted by precooling treatments with the young carp Cyprinus carpio. Electron microscopic observation of the gill and blood gas analysis were conducted. Gradual precooling or direct precooling was performed before 7°C air-exposure to reveal its prolongation effect on the survival time. In cases of gradual precooling by slowly decreasing the water temperature from 25-27°C to 7°C for the setting time, the cent percent survival curves showed convex patterns. The real maximum of the strengthening effect on the tolerance was 2h by 4h precooling. In the case of direct precooling by 7°C immersion for the setting time, the strengthening effect was not recognized. The precooling rather depressed the survival time. The cold air exposed carp received damage to gill structure, and acidosis as well as abnormally high pCO2, indicating deficiency of the repsiratory function.