GONADOSOMATIC INDEX AS A CONFOUNDING VARIABLE IN FISH-BASED SCREENING ASSAYS FOR THE DETECTION OF ANTI-ESTROGENS AND NON-AROMATIZABLE ANDROGENS.

The presence of reproductive endocrine disrupting compounds (REDCs) in the environment poses a potential threat to fish and wildlife, as exposures are capable of altering sexual development, reproductive success and behavior. Fish-based screening assays are often utilized to screen for the presence of REDCs in surface waters and to assess single chemicals for potential endocrine disrupting activity. In an effort to improve such screening assays, the goal of this project was to determine whether GSI of female fathead minnows (Pimephales promelas), as assessed via external characteristics, influences their response to REDC exposure. Specifically, we sought to determine whether low GSI females differed from high GSI females in their responses to the model anti-estrogen fadrozole and the model androgen 17β-trenbolone, and whether their was a preferable classification in the context of REDC screening. Low GSI females were more sensitive to fadrozole at the lower concentration of fadrozole (5 μg/L) and to the higher concentration of trenbolone (50 ng/L), while the high GSI females were more sensitive at the lower concentration of trenbolone (5 ng/L). The differential response of low and high GSI females to REDCs indicates that GSI influences exposure outcome, and should subsequently be taken into consideration in the implementation of screening assays, as failure to utilize fish of the appropriate reproductive status may skew test results.