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.