Characterization of Plasma Vitellogenin and Sex Hormone Concentrations during the Annual Reproductive Cycle of the Endangered Razorback Sucker

Abstract

Population declines of the endangered razorback sucker Xyrauchen texanus in the Colorado River basin have been attributed to predation by and competition with nonnative fishes, habitat alteration, and dam construction. The reproductive health and seasonal variation of the reproductive end points of razorback sucker populations are currently unknown. Using nonlethal methods, we characterized the plasma hormonal fluctuations of reproductively mature female and male razorback suckers over a 12-month period in a hatchery by measuring their vitellogenin (VTG) and three sex hormones: 17β-estradiol (E2), testosterone (T), and 11-ketotestosterone (KT). Fish were identified as reproductive or nonreproductive based on their body weight, VTG, and sex hormone profiles. In reproductive females, the E2 concentration increased in the fall and winter, and increases in T and VTG concentrations were generally associated with the spawning period. Mean T concentrations were consistently greater in reproductive females than in nonreproductive females, but this pattern was even more pronounced during the spawning period (spring). Consistently low T concentrations (<3 ng/mL) in adult females during the spawning period may indicate reproductive impairment. In reproductive males, spring increases in KT and T concentrations were associated with spawning; concentrations of E2 (<0.48 ng/mL) and VTG (<0.001 mg/mL) were low in males throughout the study. In addition, the E2 : KT ratio and T were the best metrics by which to distinguish female from male adult razorback suckers throughout the year. These metrics of reproductive health and condition may be particularly important to recovery efforts of razorback suckers given that the few remaining wild populations are located in a river where water quality and quantity issues are well documented. In addition to the size, age, and recruitment information currently considered in the recovery goals of this endangered species, reproductive end points could be included as recovery metrics with which to monitor seasonal trends and determine whether repatriated populations are cycling naturally.

Received September 24, 2010; accepted February 18, 2011

ACKNOWLEDGMENTS

The findings and conclusions in this article do not necessarily represent the views of the U.S. Fish and Wildlife Service. This project was funded by the U.S. Fish and Wildlife Service, Environmental Contaminants Program in the Division of Environmental Quality. We thank T. Lewis, M. Bell, W. Knight, R. Martin, and M. Shoemaker from Dexter for helping with the daily maintenance and monthly sampling of the razorback suckers. V. Veléz contributed to the sex hormone analysis, and M. Ellersieck provided statistical assistance. We also thank J. Calhoun, L. Fitzpatrick, P. Marsh, C. Schmitt, C. Sykes, B. Sharma, and W. Wilson for reviewing earlier versions of this document. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.