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<br />\'. <br /> <br />(1890) formally described the yellowfin trout as Salm.Q. mykiss macdonaldi. <br /> <br />When Juday studied Twin Lakes for the U.S. Fish Commission in 1902-03, he <br /> <br />found the rainbow trout to be the most common trout in the lakes (Juday 1906). <br /> <br />Juday found no yellowfin trout and although he did collect greenback trout, <br /> <br />some of these specimens show the effects of hybridization with rainbow trout, <br /> <br />and the greenback soon followed the fate of the yellowfin in Twin Lakes. <br /> <br />There are 21 specimens of ~. ~. stomias and 7 specimens of S. c. <br /> <br />macdonaldi from Twin Lakes in the collections of the U.S. National Museum <br /> <br />and the California Academy of Sciences. My examination of these specimens <br /> <br />leaves no doubt in my mind that the samples representing stomias and macdonaldi <br /> <br />were drawn from two, distinct and reproductively isolated populations of <br /> <br />cutthroat trout--at least reproductively isolated in 1889. The spotting <br /> <br />pattern and coloration differences between the stomias and macdonaldi museum <br /> <br />specimens are still strikingly distinct. Also the macdonaldi specimens <br /> <br />average two more gillrakers, 10 fewer scales in the lateral series, and six <br /> <br />fewer scales above the lateral line than the Twin Lakes specimens of stomias <br /> <br />collected at the same time. All specimens range from about 6 to 12 inches; <br /> <br />thus, these differences are not size-related. <br /> <br />HISTORICAL BACKGROUND <br /> <br />The yellowfin trout attracted much early attention because of its large <br /> <br />size. The greenback trout in Twin Lakes was small, about 12 inches maximum, <br /> <br />whereas specimens of yellowfin probably reached 10 pounds or more. Jordan <br /> <br />(1922) wrote that Mr. Fisher caught f'ive yellowfin trout from 8 to 10 pounds <br /> <br />during a morning's fishing. Other early accounts give the maximum size of <br /> <br />yellowfin trout in the 12 to 18 pound size range. Keeping in mind that <br /> <br />? <br />