Synthetic Progestin Affects Fish Reproductive Development and Behavior in Laboratory Exposure Study

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Scientists conducted laboratory experiments on levonorgestrel (a synthetic progestin) and observed differential effects to males (reproductive behavior) and females (masculinization) of eastern mosquitofish (Gambusia holbrooki).

Anal fins of mosquitofish

On the left are photos of the anal fins of female (top left) and male (bottom left) mosquitofish that were not exposed to levonorgestrel (controls). On the right are photos of female (top right) and male (bottom right) mosquitofish that were exposed to 100 nanograms per liter (ng/L) levonorgestrel (LNG, nominal concentrations) for eight days. The exposure photos show that females exposed to LNG had masculinization as evidenced by enhanced growth of the anal fin, and the males exposed to the highest LNG concentration developed elongated anal fins. Modified from Frankel and others, 2016, figures 3 and 4.

University of Maryland and U.S. Geological Survey (USGS) scientists examined the exposure effects of the synthetic progestin levonorgestrel (LNG) on the reproductive development and behavior of male and female eastern mosquitofish. Mosquitofish are viviparous (livebearing) fish that require internal fertilization and sex-specific behavioral displays to properly reproduce. Synthetic progestins, including LNG, are commonly used as components of human contraceptive and hormone replacement pharmaceuticals. Little is known, however, regarding the potential effects to aquatic organisms from exposure to such chemicals.

Scientists collaborated to conduct an 8-day laboratory aqueous exposure experiment. Eastern mosquitofish were exposed to LNG at three concentrations (0, 10, and 100 nanograms per liter, parts-per-trillion). The exposure concentrations were based on LNGconcentrations observed in wastewater effluent from the published literature. Although exposure levels based on effluent concentrations results are higher than likely expected in most streams, such levels are still environmentally relevant because it is not uncommon for some streams to be at, or approaching, 100 percent effluent under certain hydrologic conditions. Reproductive development was measured by determining anal fin (needed in males for internal fertilization of the females) length in female and male mosquitofish. The frequency of reproductive behavior was measured in paired exposure groups of males and females.

Scientists determined that LNG exposure affected female and male mosquitofish, but in substantially different ways. The females exposed to LNG exhibited physical changes (that is, masculinization evidenced by enhanced growth of the anal fin). Conversely, the males exposed to LNG exhibited behavioral changes (that is, spent less time performing courtship and reproductive behaviors). Males exposed to the highest LNG concentration developed elongated anal fins. This study documents that LNG exposures in a laboratory setting can affect the physical development and reproductive behavior of mosquitofish and indicates that these alterations could potentially affect wild fish in the environment.

This research is part of long-term investigations of the fate and effects of contaminants, including endocrine disrupting chemicals, by the USGS Toxic Substances Hydrology Program to provide water-resource managers with objective information that assists in the development of effective water management practices.

This research was funded by the USGS Ecosystems Mission Area’s Environmental Health Program (Contaminant Biology and Toxic Substances Hydrology) and supported by grants from the Cosmos Club Foundation and Morris Animal Foundation.