TEMPERATURE-ACCLIMATION OF THE PERCH (PERCA-FLUVIATILIS L) - CHANGES IN DURATION OF CARDIAC ACTION-POTENTIAL

1. Temperature acclimation for the duration of transmembrane action potential (AP) of heart ventricle was studied in vitro in the perch in winter, spring and autumn when the animals were acclimated to 2-6-degrees-C, but acclimated in the laboratory to 5 and 16-degrees-C up to 5 weeks. 2. Warm acclimation caused shortening of the AP at high temperatures. Acclimation was of Prosser's type III, rotation with an intersecting point at about 7-degrees-C. In warm acclimated fish the temperature dependency was greater than in cold acclimated fish. 3. Warm acclimation shown in the duration of the AP was more pronounced in winter and spring than in autumn. 4. It is concluded that the annual rhythm of the physiological state of eurythermic fish is an important factor for temperature acclimation.