Cooperative Fish and Wildlife Research Units Program: Arizona
Education, Research and Technical Assistance for Managing Our Natural Resources

Ultrasonic imaging, also called ultrasound, is an effective, non-lethal method used to determine sex and maturity of a variety of freshwater, anadromous, and marine fishes. However, most previous studies have been performed in laboratory environments. We developed a standardized method for ultrasonically scanning endangered Humpback Chub Gila cypha in remote locations within Grand Canyon, Arizona, USA. This method minimized stress to individual fish and took less than 1 min to perform. We were able to identify female fish with eggs based on two jpeg images and one 10 s video clip collected in the field. We also used ImageJ®, a National Institute of Health image processing program, to develop a brightness index to evaluate the maturity of eggs in female fish. We collected ultrasonic scans of captive, ripe Humpback Chub held at the Southwestern Native Aquatic Resources and Recovery Center (SNARRC) to determine that female fish were potentially ripe when a subsample of their eggs exhibited a brightness value within the 32-44 range. Although we were able to estimate egg maturity, we were not able to estimate egg mass of female fish. We successfully scanned 751 Humpback Chub in the field and collected jpeg images and video clips for each fish. Fisheries managers can use this noninvasive technique in remote or rugged field locations to collect vital information about the reproductive status of fishes that cannot be killed. A thesis on this work was completed in May, 2016, and results are published in the North American Journal of Fisheries Management. Partners were the USGS Grand Canyon Monitoring and Research Center.