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28 <br />of Dr. Behnke) from the Yampa system in Colorado were in agreement. <br />If identification of a specimen was doubtful it was usually either brought <br />back to the laboratory or various diagnostic characteristics and measure- <br />ments were taken in the field. Characteristics such as isthmus and <br />peduncle width, peritoneal lining color, principal dorsal ray counts, <br />and scale counts along and above the lateral line were recorded for <br />some catostomid specimens in the 1975 collections and almost all of <br />the catostomids collected in 1977. Techniques and procedures used in <br />these counts and measurements were those described by Beckman (1952). <br />Careful comparison of the 1977 data for field-identified catostomids <br />(Appendix V) with those reported by others for these fishes indicated <br />at least 93-percent accuracy in field identification. Almost all of the <br />questionable catostomids were probably hybrids originally identified <br />as white suckers. The field data collected from these hybrids were <br />insufficient to identify the other parental source. Therefore, they <br />were included with the white suckers as originally identified. <br />. Normally, scale samples from most field specimens were taken and <br />placed in manila envelopes, and each specimen was sexed if of a size <br />so the gonads could be seen and distinguished with the naked eye. <br />In addition, most specimens were measured to the closest 0.1 in, weighed <br />to the closest gram, and, if over 1 lb, weighed to the closest oz. <br />Weights were not taken, however, on most of the fish caught in 1977. <br />Marked Fish Studies <br />Fluorescent Pigment Marking <br />Fluorescent pigment marked rainbow trout and tetracycline-marked <br />kokanee salmon have been used previously by Wiltzius (1971, 1974) in the <br />Blue Mesa Reservoir investigations. Some fluorescent-marked rainbows