Making Unique Observations in a Very Cluttered World

Monday, 4 August 2014

Male bass switch sex - male fish with eggs in their testes show up in the Chesapeake Bay watershed -

Male bass switch sex - male fish with eggs in their testes show up in the Chesapeake Bay watershed - 

At first she was surprised. Then she was disturbed. Now she’s a little alarmed. Each time a different batch of male fish with eggs in their testes shows up in the Chesapeake Bay watershed, Vicki Blazer’s eyebrows arch a bit higher.

In the latest study, smallmouth bass and white sucker fish captured at 16 sites in the Delaware, Ohio and Susquehanna rivers in Pennsylvania had crossed over into a category called intersex, an organism with two genders.

“I did not expect to find it quite as widespread,” said Blazer, a U.S. Geological Survey biologist who studies fish. Since 2003, USGS scientists have discovered male smallmouth and largemouth bass with immature eggs in several areas of the Potomac River, including near the Blue Plains Advanced Wastewater Treatment Plant in the District.

The previous studies detected abnormal levels of compounds from chemicals such as herbicides and veterinary pharmaceuticals from farms, and from sewage system overflows near smallmouth-bass nesting areas in the Potomac.

Those endocrine-disrupting chemicals throw off functions that regulate hormones and the reproductive system. In the newest findings, at one polluted site in the Susquehanna near Hershey, Pa., 100 percent of male smallmouth bass that were sampled had eggs, Blazer said.

A magnification of a cross-section view of a smallmouth bass' testes that shows immature eggs, which are round circles on the monitor. 
With the mutant bass, she said, “we keep seeing . . . a correlation with the percent of agriculture in the watershed where we conduct a study.”

The fish that were dissected and analyzed by researchers swam downstream from farms and animal feed operations, where rains wash manure filled with various chemicals and hormones into streams and rivers.

It was a familiar finding. After the first intersex bass were found in the Potomac, the U.S. Fish and Wildlife Service made a remarkable discovery in follow-up research at Blue Plains: “We found female germ cells in the testes of 82 percent to 100 percent of the male smallmouth bass and in 23 percent of the males from . . . largemouth bass,” the agency said.

It is a problem that extends well beyond the Chesapeake Bay region, which includes the District, Virginia, Maryland, Delaware, West Virginia and Pennsylvania. Intersex bass were found by the USGS in the Columbia, Colorado and Mississippi river basins in 2009. Scientists have yet to identify a single chemical responsible for causing male fish to become part female.

In urban areas, estrogen products are often flushed down drains, contaminating water. In rural areas, natural animal hormones, much of it estrogen, is excreted in manure, which is spread on fields and washed into water by rain.

“I think it’s a complex mixture of chemicals,” said Blazer, who authored the study with nine researchers.

The findings published in Environmental Monitoring and Assessment coincided with a new report from the Environmental Integrity Project that says there is far more nitrogen and phosphorus pollution in the Chesapeake Bay than states and the Environmental Protection Agency have led residents to believe.

The report, “Murky Waters: More Accountability Needed for Agricultural Pollution in the Chesapeake Bay,” says monitoring of fertilizers and other chemicals used at farms, particularly large animal feed operations on Maryland’s Eastern Shore, is too lax under the bay cleanup plan that is being enforced by the EPA.

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