Abstract:

17α-Ethinylestradiol (EE2), a synthetic estrogen, enters aquatic environments via wastewater treatment plant effluents. Increased temperatures are of environmental concern due to climate change. These stressors influence fish growth, but the mechanism(s) remain unclear. Flow-through exposures of mummichog (Fundulus heteroclitus), an estuarine teleost, were conducted, with weight measurements taken every three days. Liver gene expression was examined by qPCR for genes known to regulate growth, including growth hormone (gh), insulin-like growth factor 1 (igf1), and their respective receptors. In Experiment 1, three-month-old mummichog were exposed to 0 or 250 ng/L EE2 at 20 and 25°C for 21 days. EE2 did not affect body weight or length; however, exposure to 25°C increased control and EE2-exposed mummichog weights by Day 12 and 18, respectively. Liver igf1ra and igf1rb mRNA expression increased in EE2-exposed mummichog at 20°C compared to their 20°C control. In Experiment 2, adult post-spawning female mummichog were exposed to the same conditions as Experiment 1. An increased temperature combined with EE2 significantly increased mummichog weights compared to the 20°C treatment groups, but not compared to the 25°C control. Mummichog at 25°C had a significantly higher gonadosomatic index (% gonad weight relative to body weight) than mummichog at 20°C. Exposure to EE2 did not affect liver somatic index (% liver weight relative to body weight). Liver igf1 and igf1rb mRNA expression increased in EE2-exposed mummichog at 25°C compared to their respective control. Variability in molecular endpoints indicates the need for further studies and to consider alternate mechanisms, including other hormonal pathways; the GH-IGF1 pathway may not be the primary mechanism involved in these growth changes when exposed to EE2 or increased temperatures.