THE RESPIRATORY METABOLISM OF EXCISED TISSUES OF WARM- AND COLD-ADAPTED FISHES

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Abstract
1. Respiratory metabolism has been studied in brain and liver tissues of two species of fish of similar mean body size, the arctic-adapted polar cod (Boreogadus saida), living at environmental temperatures of – 1.5 to + 2.0° C., and the Golden Orfe (Idus melanotus), living at an environmental temperature of 25° C. Experiments were carried out in the Warburg apparatus over the range 0-25° C. 2. Oxygen consumption in tissues of the Orfe was constant at all temperature levels studied for 180-240 minutes. In tissues of the polar cod, oxygen consumption was constant for 5-6 hours in the temperature range 0-5° C., and then the duration of the steady state decreased progressively as the temperature increased, so that at 25° C. constant oxygen consumption was observed in most cases for no longer than 40 minutes. 3. The Q10 for the steady state respiration of tissues of these two species of fish is of the same order of magnitude; values obtained were 2.08 and 2.11, respectively, for polar cod brain and liver, and 2.43 and 2.25 for Golden Orfe brain and liver. However, the Q10 remains essentially constant in the case of tissues of polar cod over the entire temperature range studied, whereas it increases sharply in Orfe tissues in the range 0-10° C. Thus, at low temperatures, the oxygen consumption of tissues of the cod, per unit weight, is several times as great as in the Orfe. These relationships are seen more strikingly when the logarithm of oxygen consumption is plotted against reciprocal of absolute temperature, or when the data are analyzed according to the Arrhenius equation. 4. These findings are discussed in relation to the problem of temperature adaptation in poikilotherms. It is concluded that the differences in response of tissues from the polar cod, compared with those of warm-adapted fish, are advantageous in adaptation of the organism to cold.