EFFECTS OF TEMPERATURE ON OXYGEN CONSUMPTION RATE IN METABOLISM OF MITOCHONDRIA ISOLATED FROM LIVEROF THE SOUTHERN CATFISH, SILURUS MERIDIONALIS CHEN

The effects of water temperature on the resting metablolic rate (Ms: mg O2/h·kg)of the southern catfish (Silurusmeridionalis Chen)and on the metabolic rate of its livermitochondriawere approached in this study.In February, 2007, 40 one-year-old juveniles of the southern catfish were divided into 5 groups for different temperature-treatments.The resting metablolicrate of each fish was measured by a continuous-flow respirometer.Then, the fish was killed and the oxygen consumption rate ofmitochondria isolated from the liver of this tested fish was determined using an oxygen electrode with succinate as metabolic sub-strate, at the same temperature as in its resting metabolismmeasurement.At the temperatures of 12.5, 17.5, 22.5, 27.5 and32.5 ℃, the resting metablolic rates of the southern catfish were 26.64, 49.03, 73.64, 102.40, 156.72mg O2/h·kg, whilethe rates of oxygen consumption by the liver mitochondria per mg of mitochondrial protein (Mp)were 12.24, 11.76, 16.28,21.56 and 31.43nmol O2/min·mg, and the rates per g of liver tissue (Mt)were 64.02, 78.72, 117.51, 121.57 and 194.20nmol O2/min· g, respectively.In orderto test the substrate preferences of the mitochondria isolated from the liver of the southerncatfish, the oxygen consumption rate of the liver mitochondria with pyruvate+malate as metabolic substrate was determined at27.5 ℃.The results showed that the rate of pyruvate+malate oxidation was significantly lower than the rate of succinate oxida-tion (p <0.05).In otherwords, the mitochodria isolated from the liver of possessed higher capacity for oxidation of succinate.Ms, Mp and Mt all increased with increasing temperature within the range of experimental temperature.Therewere double-loga-rithmic linear correlations significantly between the three kinds of metabolic rates and temperature (T: ℃), respectively.The co-variance analysis showed that the slope (temperature exponents b)in the equation forMs was significantly higher than that eitherfor Mp orforMt, i.e.the pattern of individual resting metabolism changing with temperaturewas different from that of mitochon-drial metabolism.The ratio of gross oxygen consumption in the mitochondrial metabolism to that in the resting metabolism for theexperimental group at 12.5, 17.5, 22.5, 27.5 and 32.5℃was 7.14%, 3.19%, 2.93%, 1.72%, and 2.00%, respec-tively.And the ratio for the group at the lowest temperature (12.5 ℃)was significantly higher (p <0.05)than those at othertemperatures, respectively.It was suggested by the discussion that there should be an adaptive mechanism in the livermitochon-dria of the southern catfish to resist ambient cold impact by decelerating the decline of its metabolic ratewith decreasing tempera-ture.