REACTIONS OF MARINE FISHES TO TEMPERATURE GRADIENTS

¹ From the Scripps Institution of Oceanography, La Jolla, California

An apparatus is described whereby a steep horizontal temperature (or salinity) gradient can be maintained, without the presence of vertical gradients, for the study of the reactions of fishes. The reactions of several species of marine fishes, chiefly of Girella nigricans (Ayres), to these gradients have been studied. A marked selection was demonstrated of temperatures which were relatively high in comparison with the normal environment of the fishes. The influence of acclimatization and of other factors upon temperature selection was investigated. While acclimatization was found to influence selection, the effect was slight and only temporary, the selected temperature being, to a large extent, independent of past experience. The physiological and ecological significance of selection in the experimental gradient is discussed. The rôle of contrast and of rapid "adaptation" is indicated. It is concluded that selection is indicative of the relative stimulative or detrimental effects of given rapid changes of temperature, while the common view that such selection indicates the nature of "optimal" conditions or habitat preference is not tenable.