TEMPERATURE PREFERENCE IN 2 POPULATIONS OF JUVENILE COHO SALMON, ONCORHYNCHUS-KISUTCH

Two groups of coho salmon, Oncorhynchus kisutch, were raised under ide ntical regimes to test the hypothesis that the group from a stream wit h lower and less variable temperatures would have a lower and less var iable preferred temperature than would the group from a stream with wa rmer and more variable temperatures. The preferred (modal) temperature s in an electronic shuttlebox of coho salmon young from a relatively c ool, groundwater-fed stream were slightly lower and less variable than those of young from a warmer and more heterothermal stream (mean = 9. 6 degrees CI range: 6-16 degrees C vs. mean = 11.6 degrees C, range: 7 -21 degrees C). However, there was a great deal of variation within an d among individual fish. While some genetic variation in thermal prefe rence may exist, the species seems best characterized as tolerant of r elatively large temperature fluctuations.