Use of Ultrasonic Imaging and Ovaprim® to Evaluate Egg Maturation of Humpback Chub Gila Cypha

Although nine known aggregations of humpback chub, Gila cypha, currently exist in the main stem Colorado River in the Grand Canyon, little is known about their reproduction. It has been hypothesized that water temperatures of the main stem Colorado River below Glen Canyon Dam are too low due to hypolimnetic dam releases for female humpback chub to develop eggs for spawning. In this study, we evaluate use of ultrasonic imaging and Ovaprim® to identify egg development in female humpback chub. In addition, we document locations of female chub with developing eggs in the Colorado River drainage, especially the main stem below Glen Canyon Dam. Based on our initial results, we conclude that ultrasonic imaging is an effective method for identifying egg development in female humpback chub.