Factors influencing the orientation of migrating anadromous fishes

Abstract

The purpose of this investigation was to examine experimentally the influence of certain physical and chemical water characteristics upon the orientation of one type of migrating anadromous fish. The reactions of more than 8000 fish of the genus Pomolobus-alewife, P. pseudoharen gus and glut herring, P. aestivalis were tested as the fish migrated upstream through the Herring River at Hourrnedale, Mass., toward their spawning area, in the springs of 1949 and 1950. The findings of this investigation were: presented with a choice of waters having different temperatures, 77% of the fish entered the channel with the warmer water when the temperture difference continuously exceeded 0.5/sup 0/C. The response of the fish to temperature differences near the threshold difference decreased as the temperature level of the water increased. 72% of the fish entered the channel with water of a lower free CO/sub 2/ content when the free CO/sub 2/ diffence exceeded 0.3 ppM. The sex of the fish appeared to have no influence on its response to differences in CO/sub 2/ content or in temperature. Exploratory experiments indicated that visual factors and such factors as velocity and turbulence can influence orientation. The fish did not respond to a difference of 1.1more » ppM. O/sub 2/ created during experiments. The fish were indifferent to pH differences as large as 0.8 pH unit when associated differences in free CO/sub 2/ were less than the threshold 0.3 ppM The relative orientative influence of CO/sub 2/ and temperature, was shown to depend upon their relative differences of magnitude. The behavior of the fish indicated that the orientation was accomplished by a method of trial involving both movement of the fish and a comparison of intensities of stimulations which were successive in time.« less