Even fisheries scientists can have a difficult time determining whether a fish is male or female by just glancing at it. So, imagine if you had a hatchery full of several hundred fish that you hope to breed in order to sustain an endangered species. In a recent article in the North American Journal of Aquaculture, scientists from NOAA’s National Marine Fisheries Service Manchester Research Station, Washington, are using ultrasound technology to determine the sex and the sexual maturity of endangered Redfish Lake Sockeye Salmon used as hatchery broodstock. The researchers use a complex spawning matrix in order to retain the genetic diversity of the broodstock, so knowing the sex and maturity of each fish is vital. Maturing fish also need to transition into freshwater and off of feeding four to five months prior to maturity. Sonography has been widely used over the years to examine fish for many purposes, including identifying sex and reproductive readiness. In this case, the fish are placed belly-up in a v-shaped cradle in a pan filled with anesthetic-treated water and the probe is run along the abdomen until the gonads are visible on the screen. The station has achieved an average 97.7% accuracy rate in determining the sex and maturity of 3-year-old Sockeye Salmon four to five months before spawning. Methods and Accuracy of Sexing Sockeye Salmon Using Ultrasound for Captive Broodstock Management, by Deborah A. Frost, W. Carlin McAuley, Bryon Kluver, Mike Wastel, Desmond Maynard, and Thomas A. Flagg. North American Journal of Aquaculture 76:153-158.