Masters Theses

Date of Award

5-1994

Degree Type

Thesis

Degree Name

Master of Science

Major

Life Sciences

Major Professor

S. Marshall Adams

Committee Members

Mark Greeley Jr., Walter Farkas, Richard Strange

Abstract

Serum or plasma levels of reproductive steroids are increasingly being utilized as biomarkers of reproductive dysfunction in biological assessments of environmental contamination. Diel, seasonal, and reproductive stage- dependent variations in steroid concentrations are rarely considered in studies of this type. The potential implications of these sources of variation are greatest in organisms that produce more than one clutch of eggs or young per year. In this thesis, the use of serum levels of 17Β-estradiol and testosterone in biomonitoring efforts emphasizing fish reproduction was examined in a multiple-spawning freshwater teleost. Radioimmunoassay methods for measuring 17Β-estradiol and testosterone in female redbreast sunfish (Lepomis auritus) serum were validated and used to determine circulating levels of these steroids. The natural seasonal variation in circulating levels of 17Β-estradiol and testosterone in adult female redbreast sunfish was presented along with the seasonal variation in other reproductive parameters such as frequency of vitellogenic oocytes in the ovary and gonadosomatic index (GSI). Staging systems for redbreast sunfish oocytes and ovaries were proposed and utilized to determine the naturally occurring variation in 17Β-estradiol and testosterone due to reproductive stage. Field trials utilizing serum levels of17Β-estradiol and testosterone along with a suite of other reproductive indicators were conducted at three different sets of contaminated and reference streams. As expected, serum levels of 17Β-estradiol and testosterone exhibited pronounced natural seasonal and stage-dependent variability. Therefore, for valid site-to-site comparisons of serum levels of 17Β -estradiol and testosterone, samples should be standardized by season and reproductive stage as closely as possible because of the significant natural variation occurring in 17Β estradiol and testosterone levels. Furthermore, serum levels of 17Β-estradiol and testosterone are best used in assessments of the physiological and ecological effects of environmental contamination as part of a larger suite of reproductive biomarkers and other biomarkers that reflect contaminant stress at other levels of biological organization.

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