Methods and Accuracy of Sexing Sockeye Salmon Using Ultrasound for Captive Broodstock Management

Abstract

AbstractUltrasound has been widely used to noninvasively examine the internal anatomy and reproductive status of many fish species. Since 2003, ultrasonography has been an integral part of broodstock management for Endangered Species Act–listed endangered Redfish Lake Sockeye Salmon Oncorhynchus nerka. Initial ultrasound screenings for each year's broodstock were conducted 3 to 4 months prior to anticipated maturation, before external signs of maturation developed. In keeping with the natural life history of these fish, this permitted the separation of nonmaturing fish from maturing fish so the immature fish could maintain feeding and growth. It also permitted maturing seawater‐reared fish to be transferred to freshwater for final maturation. Designing a spawning matrix to maintain genetic diversity requires knowledge of the sex of each fish before spawning. Approximately 1 month prior to spawning, a second ultrasound was performed to verify sex identification and thus ensure the accuracy of the spawning matrix. Over a 9‐year period, 2,662 fish were examined. The accuracy of sexing age‐3 adult Sockeye Salmon ranged from 94.0% to 100%, with an average of 97.7%, while the accuracy of sexing age‐4 adult fish ranged from 92.0% to 100%, with an average of 94.4%. The average accuracy was similar for fish examined in seawater or freshwater (98.1% versus 97.3%, respectively). Ultrasound was shown to be an accurate and effective tool for managing the husbandry of our captive broodstock life history.