Earlier work by a team of US and Canadian scientists had already shown that, in a small lake deliberately contaminated with estradiol, the population of fathead minnows declined sharply. "They attributed that to reproduction failure," he said. "My data suggest it could be, in addition, an impact on larval survival."
To find out more, Rearick compared gene expression in estradiol-exposed and unexposed fish. He found a significant increase in the expression of genes for the neurotransmitter dopamine in estradiol-exposed fish, suggesting that something might be occurring in their developing brains.
Klaper took a similar approach in her investigation of fluoxetine effects in fathead minnows, finding a cascade of gene-expression changes in the male minnows' brains as the dose increased. "I'm in the process now of trying to figure out the [physiological] pathways these might be involved in," she said.