A method is described for measuring the preferential responses of fish to alterations in the chemical and physical nature of their environment. Changes in the responses of young chum salmon at various stages of growth to alterations in the environmental sea water content have been studied. The effects of small alterations in temperature (2 to 3 C° ) and in rates of flow of environmental liquids on the fishes' responses to salinity change, were also studied. Preliminary experiments on the responses of coho salmon fry to sea water are described. The results indicate that changes in the environmental sea water content, such as those encountered in the estuaries of salmon streams may exert a directive influence on the seaward movement of chum salmon fry. / Science, Faculty of / Zoology, Department of / Graduate