Simultaneous direct and indirect calorimetry together with biochemical determinations of metabolite concentrations were used to compare the normoxic and anoxic energy metabolism of goldfish at 20°C. The normoxic and anoxic heat production levels determined by direct calorimetry were in agreement with previous results: 700 and 200Jh−1MW−1, respectively (where MW is metabolic weight, kg0.85). Metabolite determinations during normoxia and after 3 and 8 h of anoxia showed that during anoxia a thermodynamic steady state is reached. By simultaneous calorimetry the amounts of oxidized substrates during normoxia and anoxia and the amount of excreted ethanol, the end product of incomplete anaerobic oxidation, as well as normoxic and anoxic carbon dioxide production were determined. During normoxia and anoxia the same substrates for oxidation are used (carbohydrate and protein) by small starving goldfish, but the end products are different. During normoxia oxidation is complete (to CO2 and H2O; protein oxidation also has ammonia as an end product, but this is considered physiologically as complete oxidation), whereas during anoxia oxidation is incomplete, with ethanol, which is excreted, and CO2 as end products. From the indirect calorimetric calculations it appeared that anoxic goldfish also produce fat. Glycogen storage appears to be crucial in the anoxia survival strategy.

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