Accuracy of histology, endoscopy, ultrasonography, and plasma sex steroids in describing the population reproductive structure of hatchery‐origin and wild white sturgeon

Hatchery‐origin white sturgeon Acipenser transmontanus in the lower Columbia River, Canada are approaching puberty, and describing the reproductive structure of the population is critical to determine if they are capable of contributing to spawning events in the wild, a key management uncertainty. Few studies have compared the accuracy of available tools (histology, ultrasound, endoscopy, and plasma sex steroids) used to assign sex and stage of maturity within the same population of prepubertal and post‐pubertal sturgeon. Population reproductive structure was described using these tools in 332 hatchery‐origin and 75 wild individuals over 2 years (2017 and 2018). True sex was determined using histological analysis of gonadal tissue, which is 100% accurate at assigning sex and stage of maturity in fish when germ cells are present in the biopsy. All hatchery‐origin fish assessed had not reached puberty and were pre‐meiotic males (n = 158) or pre‐vitellogenic females (n = 174). Assignment of true sex using histology was 97% in hatchery‐origin and 94% in wild fish as several biopsies did not contain germ cells. Fish with gonadal biopsies that did not contain germ cells and intersex fish (n = 3) were not included in further analyses of other tools. Accuracy in assigning sex to both the hatchery‐origin (98%) and wild (100%) fish was highest using endoscopy (an otoscope). The other tools evaluated were less accurate, with 69% accuracy in hatchery‐origin and 74% accuracy in wild fish for plasma sex steroids and 57% accuracy in hatchery‐origin and 70% accuracy in wild fish for ultrasonography. Based on these results, endoscopy was the most reliable tool for assigning sex in both prepubertal and post‐pubertal fish and can be easily complimented with histology when determining stage of maturity or describing population reproductive structure.