Potential Classification of Sex and Stage of Gonadal Maturity of Wild White Sturgeon Using Blood Plasma Indicators

Abstract

Because white sturgeon Acipenser transmontanus show no readily discernible external signs of gender, management agencies use surgical biopsies to determine the sex and stage of gonadal maturity of individuals. This procedure is highly invasive and can be difficult under field conditions. Therefore, gonadal tissue and blood were collected from white sturgeon captured in tribal and commercial fisheries (fishery fish) and by fish and wildlife agencies (oversize fish) in the Columbia River basin to develop a method of determining sex and stage of maturity using the blood plasma indicators testosterone (T), 11-ketotestosterone (KT), estradiol (E2), and calcium (Ca²⁺). The sex and stage of maturity was determined by histology or by visual examination in maturing fish. Plasma sex steroid levels were measured by radioimmunoassay, and plasma Ca²⁺ was measured spectrophotometrically. White sturgeon showed sex- and maturity-specific levels of steroids and Ca²⁺. Stepwise discriminant function analysis (DFA) was used to choose the best variable(s) for predicting sex and stage of maturity, and quadratic DFA was conducted to classify fish into two groups of sex or four groups of sex and stage of maturity. In the classification of the fishery plus oversize fish, plasma T and E2 were the best predictors of sex and stage of maturity. Of the 151 females and 106 males, 85% of the females and 79% of the males were correctly classified; 88, 72, 98, and 96% of the immature females, immature males, maturing females, and maturing males, respectively, were correctly classified. The greatest error of misclassification occurred with immature males classified as immature females. In the analysis of immature fishery fish only, plasma T and fork length led to the correct classification of 88% of the females and 86% of the males. In the analysis of oversize fish only, 100% of the females and 95% of the males were correctly classified using plasma T and E2; 93, 100, 98, and 100% of the immature females, immature males, maturing females, and maturing males, respectively, were correctly classified using these variables. The derived classification functions for the prediction of sex or sex and maturity may replace the need for surgical biopsies if the error associated with the misclassification of immature fish is acceptable.