EXPOSURE EFFECTS OF ENVIRONMENTAL GESTAGENS ON THE REPRODUCTIVE BEHAVIOR AND FITNESS OF THE FATHEAD MINNOW (PIMEPHALES PROMELAS)

Abstract

Historically, endocrine disrupting chemical research has focused on environmental androgens, estrogens, thyroid hormones, and their antagonists. Recent efforts have begun to examine the effects of gestagens, which include endogenous progestogens and synthetic progestins, on aquatic organisms. Gestagens have been measured in wastewater treatment plant effluent, pulp mill effluent, and runoff from agricultural fields. While studies have documented profound effects on the reproduction of fish and amphibians, the effects of gestagen exposure on reproductive behavior and male gamete quality have been relatively unexplored. As such, a series of studies were conducted in which fathead minnows (Pimephales promelas) were exposed to either a water control, EtOH control, or one of two concentrations of gestodene (GES), levonorgestrel (LNG), or progesterone (P4) using a flow-through exposure system. Egg deposition was quantified daily, and alterations of reproductive behavior were examined on days 1, 2, and 8. After 8 days, fish were examined for the presence of secondary sexual characteristics (i.e. nuptial tubercle, fin spot, and dorsal fatpad formation). Egg deposition was affected by all treatments, with complete cessation observed at higher concentrations. Reproductive behaviors were affected after just one day in response to both treatments of LNG, GES, and P4, with effects continuing through days 2 and 8. Exposure to both concentrations of LNG and GES also caused the physical masculinization of female fathead minnows. In a second set of studies using computer assisted sperm analysis, the same treatments were utilized to determine effects on sperm motility in males as a result of in vivo or in vitro exposure. LNG and GES showed no effect in either study, and P4 caused decreases in sperm motility only as a result of in vivo exposure. Together, results from this study indicate that both GES and LNG function as environmental androgens in fishes, causing masculinization of secondary sex characteristics in females and disruption of reproduction over a short period of time. As altered reproductive behavior was observed after just one day of exposure for all treatments, this study underscores that behavior is an extremely sensitive endpoint that merits increased attention in future aquatic toxicology studies.