Some Experiments On Thermal Acclimation in the Goldfish (Carassius Auratus L.)

Abstract

1. Goldfish with a body weight ranging from 40 to 110 grams were acclimated to 15°C and 30°C. The oxygen consumption rates of fish swimming at a constant speed were measured at the acclimation temperature and at temperatures deviating from the acclimation level. Swimming goldfish show thermal compensation in the oxygen uptake rates. 2. The oxygen consumption rates and critical oxygen concentrations of goldfish were measured in specimens swimming at a constant speed and at acclimation temperature in different salinities. When the osmotic gradient between the internal and external milieus declines, the O 2 consumption rate increases and the critical O 2 concentration decreases. This finding supports the view that respiration rate of fish is a compromise between the demands of gastransport and osmoregulation. 3. The rate of oxygen consumption of propulsion muscles shows thermal compensation. Acclimation to a change from 15°C to 30°C requires 4 to 5 weeks, according to the criterion of succinate-oxidase system activity. 4. The activity of glucose-6-phosphate dehydrogenese, lactate dehydrogenase, and -hydroxyacyl-CoA dehydrogenase of muscle tissues does not exhibit thermal compensation, as judged from comparison of the 15°C and 30°C levels. During acclimation from 15°C to 30°C, the activity of both succinate dehydrogenase and malate dehydrogenase of red lateral muscle decreases and that of -glycerophosphate dehydrogenase increases. The lactate dehydrogenase isozymic pattern of goldfish muscle is dependent on the acclimation temperature. 5. During thermal adaptation from 15°C to 30°C there is: a) a relative decrease of the oxygen consumption rate of swimming fish, b) a lowering of the oxidative capacity of the propulsion muscles, c) a change in the muscular lactate dehydrogenase isozymic pattern in the direction of a probably more anaerobic pattern, and d) a shift in quantitative importance from the muscular malate shuttle to the a-glycerophosphate shuttle. These points are consistent with the view that metabolism of the propulsion muscles of the goldfish changes into a more anaerobic type, so that the initial increase of the ventilation rate can be reduced during adaptation to the higher temperature.