STUDIES OF THE RESPIRATORY METABOLISM OF WARM AND COOL SPRING FISHES 1 F. B. SUMNER AND URLESS N. LANHAM I. INTRODUCTION It is generally agreed that the respiratory metabolism (oxygen con-sumption) of poikilothermal animals tends to vary directly with the tem-perature to which they are subjected. Less familiar is the existence of a process of thermal adaptation, following transfer from one temperature to another. The immediate effects of such transfer may be succeeded by a "rebound" from the extreme condition first induced back toward the previous condition of the animal. A further illustration of the same principle is the fact that the metabolic rate of fishes at any given tem-perature may be considerably influenced by their previous temperature experience. Fishes which had been acclimatized to 30, for example, showed a lower rate of oxygen consumption, when transferred to 20, than ones which had been kept continuously at 20, and conversely, transfer from 10 to 20 resulted in a higher rate than that shown by fishes accustomed to the latter temperature. Here, too, any such depar-ture from the normal oxygen consumption for a given temperature is followed, within a few days, by a process of adaptation which tends to equalize the metabolic rate, regardless of previous history (Wells, 1935&; Sumner and Wells, 1935; Sumner and Doudoroff, 1938). An obvious question is whether the metabolic rate of fishes and other poikilothermal animals in nature varies as widely with the temperature of their medium as might be inferred from these laboratory results. Or, may not more far-reaching processes of adaptive modification occur in nature, such that warm-water and cold-water derivatives of the same stock come to have nearly the same rates of metabolism? Fox and Wingfield 2 compared certain closely related species, or local representatives of the same species, living at different latitudes, and re-ported varying degrees of thermal adaptation of this sort. In some cases, there was no such adaptation, the two forms under comparison differing widely under their own normal conditions of life, but approximating one 1 Contributions from the Scripps Institution of Oceanography of the University of California, La Jolla, California, New Series No. 157. Services were rendered in the course of these studies by persons working under W.P.A. Project 65-1-07-2317. 2 Fox, 1936, 1939a, 1939b ; Fox and Wingfield, 1937 ; Wingfield, 1939. 313
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