Studies of fish sharing male and female characteristics

Spiel · October 10, 2009

Studies of fish sharing male and female characteristics raise concerns about Great Lakes contaminants

Oct. 9, 2009

Fish with characteristics of both genders are more prevalent than previously thought in U.S. rivers, according to a recent U.S. Geological Survey study.

While this study did not analyze fish in the Great Lakes, it may raise new concerns as to whether previously noted hermaphrodite fish in this region are becoming more prevalent as well.

“Until we take current sampling it is hard to know,” said Chris Metcalf, director of the Institute for Watershed Science at Trent University in Ontario. “However, all studies are symptomatic of more estrogens being discharged into streams.”

Fish with reproductive characteristics of both sexes are known as intersex, a condition linked to exposure to estrogenic compounds. Such compounds can disrupt the endocrine system that regulates growth, metabolism, and reproductive processes. These compounds are commonly found in pharmaceuticals and personal care products.

The study appeared in the journal Aquatic Toxicology. It comes as the International Joint Commission raises concerns about emerging contaminants in the Great Lakes.

“Fish are incredibly plastic when it comes to sex, and they are very responsive to environmental estrogens and androgens,” said Cheryl Murphy, assistant professor in the Department of Fisheries and Wildlife at Michigan State University.

In this study, fish collected from eight out of nine river basins, from 1994 to 2004, were found to have both sex characteristics. Ninety-seven out of 3,110 were found to have characteristics of both genders. Ninety-six of these were males that exhibited female characteristics.

Jo Ellen Hinck, lead author of this study, said a lot of compounds of concern are estrogenic.

“These compounds can enter the fish and increase estrogen levels in female fish,” she said “However, when males get an extra boost of estrogen it can have more of an apparent effect.”

Studies published in both 2004 and 2008 have confirmed the presence of intersex white perch in the lower Great Lakes, specifically Lake Ontario.

Intersex white perch were found in waterways close to discharge pipes from sewage treatment plants. The study, published in Environmental Health Perspectives in 2004, found 83 percent of white perch were intersex at a location in the lower Great Lakes.

Metcalfe, who is also a professor and researcher at Trent University, was one of several researchers involved in this study. He said that white perch may have been more susceptible to this condition because when they are younger they are relatively sedentary, which would be problematic if they were close to a sewage discharge.

Researchers in the 2004 study concluded that intersex changes most likely occurred from exposures to estrogenic compounds and other pollutants. Fish experiencing both reproductive features were more prevalent in areas with high levels of water contamination, the study reported.

While more research must be conducted to determine whether human consumption of intersex fish can produce harmful effects, there is information that suggests that intake of certain chemicals in fish can cause health ramifications, said Dr. George Abela, cardiologist at the Michigan State University Clinical Center.

“If the contaminant is persistent then humans that eat the fish can accumulate that contaminant in their body,” Murphy said.

“Because the variety of hormones and chemical messengers are remarkably conserved across the animal kingdom, contaminants that cause intersex in fish can also potentially cause some type of endocrine disruption in humans,” she said.

Metcalf said that natural estrogens, which can be found in birth control, may not be of great concern. However, chemicals such as bisphenol A, which are used to make plastics, can mimic estrogens and can cause problems in humans.

Abela said that consuming fish with contaminants does not have a significant impact on the heart, but can have damaging effects on the human brain and gastrointestinal lining.

The health effects that this condition has on fish itself are still unknown. However, Hinck said that some studies have hypothesized that it may affect the integrity of male sperm.

In the recent study on U.S. rivers, which included the Mississippi River and Yukon River Basins, the intersex condition was observed in catfish, carp, smallmouth bass and largemouth bass, but was most prevalent in smallmouth bass.

Hinck said that her study could not conclude that estrogenic compounds or pollutants were directly linked with intersex occurrences. This could be a likely cause given the results of other research studies. However, further lab tests and sampling must occur.

She said that a variety of factors could have led to these occurrences in her study, such as water pH, steroids, pollutants and water temperature.

“[This study] will hopefully highlight that we don’t know what this condition means for individual fish and the whole fish community,” Hinck said.

Murphy, who studies the effects of endocrine disruptors in fish, said more information needs to be known before deciding what actions need to be implemented as a result of these findings.

“To combat the problem, you first have to determine what is inducing intersex and the source of the stressor,” she said. “If pharmaceuticals from sewage are inducing intersex, then the sewage would have to be treated to specifically remove the endocrine active compounds before it is released. If it is PCBs, the sediment containing PCBs would have to be dredged.”

PCBs, or polychlorinated biphenyls, were once used for many different purposes ranging from flame retardants to pesticides. Along with mercury and other contaminants, PCBs continue to be of high concern in all of the five Great Lakes.