Exposure to estrogen reduces production of immune-related proteins in fish. This suggests that certain compounds, known as endocrine disruptors, may make fish more susceptible to disease. Results of the study were published online Wednesday in the journal, Fish & Shellfish Immunology. The study, led by U.S. Geological Survey genomics researcher Dr. Laura Robertson, revealed that largemouth bass injected with estrogen produced lowered levels of hepcidin, an important iron- regulating hormone in mammals that is also found in fish and amphibians. This is the first published study demonstrating control of hepcidin by estrogen in any animal. Besides being an important iron-regulating hormone, researchers also suspect that hepcidin may act as an antimicrobial peptide in mammals, fish and frogs. Antimicrobial peptides are the first line of defense against disease-causing bacteria and some fungi and viruses in vertebrate animals. Study conducted by Robertson and her colleagues showed that largemouth bass produced two different hepcidin proteins. Production of the first hepcidin protein was 'turned down' by estrogen. Production of the second hepcidin protein by fish exposed to bacteria was blocked by estrogen. 'Our research suggests that estrogen-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. 