Male smallmouth bass with female traits have turned up in the Susquehanna River, the second major Chesapeake Bay tributary where "intersex" fish have been detected. A federal scientist said Tuesday she's investigating whether the abnormality could be linked to farm or consumer chemicals getting into the river.
More than 90 percent of adult male bass examined in the Susquehanna in the past year had immature egg cells in their testes, said Vicki Blazer, a fishery biologist with the U.S. Geological Survey. Blazer, who previously has documented the phenomenon among fish in the Potomac River watershed, presented her latest findings at a meeting in Baltimore of the American College of Veterinary Pathologists.
Blazer said she found the intersex condition in Susquehanna bass while studying bacterial and fungal infections and lesions among the fish, which have drawn scientific scrutiny because of repeated die-offs the past few years of their newly hatched young. Investigations of fish kills in the Potomac, Shenandoah and Monacacy rivers turned up infections and lesions among survivors as well as the intersex condition.
Such interesex traits are an indication of animals being exposed to hormonelike chemicals, and Blazer has previously found the condition frequently among smallmouth bass caught on stretches of the Potomac and its tributaries where farming is intense or where development is dense.
Initially, the federal biologist suspected chronic low-level exposure of fish to pharmaceutical drugs and personal-care products, which are flushed down toilets and drains and show up in discharges from wastewater treatment plants. But Blazer said her research failed to find any greater frequency of intersex fish downstream from wastewater plants, prompting her to broaden the possible list of chemical exposures to include agriculture.
"What we're really looking at is complex mixtures," she said, of traces of many different chemicals.
A recent study found intersex fish more often downstream from large-scale animal farming operations, Blazer said, noting that poultry feed has contained traces of toxic arsenic. And the intersex condition is found more in spring, she said, when fish spawn and farmers treat their fields with atrazine, a herbicide used widely around planting time. Low levels of atrazine are widely detected in streams, especially in spring, and some researchers have found exposure to the chemical affects reproduction in frogs and fish — a linkage disputed by other scientists.
Syngenta, which manufactures atrazine, issued a statement saying it was unaware of any research by Blazer linking intersex fish with exposure to its herbicide. The company cited six other studies it said showed the safety of its product to fish populations and that found no effect on fish reproduction. The studies, half from the 1970s, evaluated atrazine exposure on fathead minnows, bluegill and brook trout.
While smallmouth bass remain relatively abundant in the Potomac, anglers and scientists alike have grown concerned over a dropoff in the fish in the Susquehanna in recent years. Geoffrey Smith, a biologist with the Pennsylvania Fish and Boat Commission, said die-offs of young bass occurred in 2007, 2008 and again this year. But the immediate cause appears to be bacterial and fungal infections, he said, not necessarily the intersex condition Blazer has found. It's not clear what, if any, connection there is, he said.
"We're on the cutting edge of this," Smith said. He suggested that smallmouth bass might simply be more prone to the sexual mixup, noting that it doesn't show up as much in other closely related fish species.
Concerned over the years-long decline in smallmouth bass in the lower Susquehanna and Juniata rivers, Pennsylvania moved last month to preserve the remaining fish by requiring anglers to release any they catch. The restriction is meant to maintain as many adult bass as possible until their reproduction rebounds, Smith said.
He also suggested that poor water quality caused by more conventional pollution might have stressed the Susquehanna fish and made them more vulnerable to disease. Scientists have documented severe dips in fish-sustaining oxygen in the water at night, the biologist said, which appear to be a byproduct of algae blooms fed by high levels of phosphorus in the river. The Susquehanna, like the rest of the bay's rivers, is choked with phosphorus and nitrogen from treated wastewater, from farm animal manure, and from lawn and crop fertilizers.
Blazer said more study is needed because she has sampled only a limited number of Susquehanna fish. She said she plans to test the impact of various low-level chemical exposures on young smallmouth bass at the National Fish Health Research Laboratory in Kearneysville, W.Va., where she works. Another study is being considered to look for possible links between fish illness and abnormalities and their food supply, she said.