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12` <br />all sampling periods. During some months, transects were also run at <br />depths of 2.7 m and 5.2 m. Substrate types and temperatures were <br />recorded at each sample location. Positive identification and stages of <br />development were determined for each larvae collected (Snyder 1981). <br />Only 50% of the larvae were processed when collections exceeded 300 <br />individuals. Total lengths of larvae were recorded for 20-30 larvae per <br />sample. Most larvae were returned to the lake while some were brought <br />back to UNLV for behavioral observations in an artificial stream. <br />3.6 Temperature Development Analyses. <br />Temperature-development analyses of egg and larval stages of <br />razorback suckers were conducted in the laboratory. Eggs were collected <br />from gravid females and fertilized in the field using a 6 : 2 <br />male/female ratio. Upon fertilization, eggs were counted and transferred <br />to the laboratory in lake water on natural, gravel substrates. Adults <br />were released back into the reservoir. Ambient reservoir temperature was <br />maintained during transport to the laboratory. Eggs were acclimated from <br />ambient lake temperatures to experimental laboratory temperatures at the <br />rate of I°C per hour and kept within 1.5°C throughout the experiments. <br />Rates of development were followed through various egg and larval <br />stages, and hatching success was recorded at each experimental <br />temperature. <br />Laboratory development data were used to determine spawning dates <br />of field-collected larvae. Development times at particular stages were <br />converted to standardized thermal units using the formula: (Heming et <br />al. 1982) <br />TU = days at temp. X °C <br />24