The Selected Temperature of Atlantic Salmon and Speckled Trout and the Effect of Temperature on the Response to an Electrical Stimulus

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Abstract
When confined to a long narrow trough, speckled trout (Salvelinus fontinalis) and Atlantic salmon (Salmo salar) responded to the passage of an electric current (condenser discharge) through the water by making a relatively discreat movement forward. The avg. distance covered in such "darts" varied with the temp. of the water in the trough. It was max. for trout at 9-10[degree] C and Cor salmon at 14-15[degree]C. Tested in a gradient of temp. the locomotion of single fish or of groups of fish tended to confine the organisms to a specific narrow range of temps. This "selected temp,"was about 10 [degree]C in the case of trout but 14 [degree]C in the case of salmon. It is evident that the selected temp. and the temp. at which the response to the electrical stimulus is max. are for practical purposes identical. Temp. selection is the response of a moving animal to a temp. gradient. Each locomotory movement of the whole animal is completely described in terms of its direction, length, and duration in time. Some effect of temp. on one or more of these attributes of the movements must therefore Head to temp. selection. The effect of temp. on responses to the electrical stimulus suggests that it may be the length of the individual movements which is modified by the temp. in such a way as to result in selection.
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