Exposure to estrogen reduces production of immune-related proteins in fish, according to new lab tests conducted by scientists from the U.S. Geological Survey.
The researchers say that this finding suggests that certain compounds, known as endocrine disruptors, may make fish more susceptible to disease.
According to them, their study may provide new clues for why intersex fish, fish kills and fish lesions often occur together in the Shenandoah and Potomac rivers.
Dr. Laura Robertson, who led the study, said that largemouth bass injected with oestrogen produced lowered levels of hepcidin, an important iron-regulating hormone in mammals that is also found in fish and amphibians.
This is the first time that any study has demonstrated control of hepcidin by oestrogen in any animal.
It is believed that besides being an important iron-regulating hormone, hepcidin may also act as an antimicrobial peptide in mammals, fish and frogs-the first line of defence against disease-causing bacteria and some fungi and viruses in vertebrate animals.
"Our research suggests that oestrogen-mimicking compounds may make fish more susceptible to disease by blocking production of hepcidin and other immune-related proteins that help protect fish against disease-causing bacteria," said Robertson.
The study showed that largemouth bass produced two different hepcidin proteins. Production of the first hepcidin protein was "turned down" by oestrogen. Production of the second hepcidin protein by fish exposed to bacteria was blocked by oestrogen.
The fact that oestrogen blocked production of hepcidins in fish exposed to bacteria gives more weight to the theory that oestrogen or oestrogen-mimicking chemicals could be making fish more susceptible to diseases, Robertson said.
A research paper on the study has been published in the journal, Fish and Shellfish Immunology.