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30 <br />at least 95 percent of Age 1+ fish still had pigment. All rainbows <br />collected from Morrow Point and Crystal Reservoirs during this period <br />were also examined for marks, and many of the rainbows from the lower <br />river samplings were also examined. <br />Tetracycline Marking <br />This technique involves feeding a diet containing oxytetracycline <br />at the hatchery. The additive leaves a detectable yellow mark in the <br />bones when fluoresced with ultraviolet light. The technique was described <br />in detail by Wiltzius (1971). The only change from that originally <br />described is the duration of the feeding and the size when experimental <br />lots were fed. In May 1974, 800,000 kokanee salmon (approximately 40 <br />percent of all salmon stocked in Blue Mesa that year) at a count-weight <br />of about 1000/lb were fed for 9 consecutive days. A sample of these <br />fish was held indoors at Roaring Judy Hatchery until September 1974, <br />when 99 percent of them were found to contain a detectible mark. It <br />should be noted here that direct sunlight can destroy a tetracycline <br />mark in less than 30 days in smaller salmon held outdoors (Wiltzius <br />1971). Sampling was therefore scheduled for Blue Mesa Reservoir to de- <br />termine if the mark was being retained. <br />In the spring of 1975 the entire plant (240,000) of kokanee scheduled <br />for Taylor Park Reservoir was also marked with tetracycline. Subsequent <br />downstream sampling was done to determine out-migration of the salmon. <br />Generally, the tail section, including the last few vertebrae, was col- <br />lected from each salmon taken during this study. If the vertebrae could <br />not be examined in the laboratory under a 100-W ultraviolet source with a <br />dissecting microscope, the sample was frozen for later examination. Most <br />bone samples were examined within 24 hrs of collection.