Scientists say 60 percent of male Missisquoi fish bear eggs


A painting of smallmouth bass by Timothy Knepp. U.S. Fish and Wildlife Service image

A significant majority of Missisquoi River’s male smallmouth bass bear eggs, a characteristic known as “intersex.”

Researchers believe the condition results from agricultural runoff in the Missisquoi River watershed, an area where farmers already face scrutiny for phosphorus pollution that promotes blue-green algae blooms in Lake Champlain.

A report published this fall, the most comprehensive of its kind, found 60 percent to 75 percent of male smallmouth bass in the Missisquoi River carry eggs.

Agency of Agriculture officials say the report does not establish farming as the cause of the dual sex traits in fish, and say that Vermont’s piscene population actually showed less incidence of androgyny than those of other states in the study.

Clean-water advocates have called on legislators and state agencies to take action in response.

“The alarm to me is that these chemicals are present — they’re in our water, they’re in our food, we’re exposing ourselves to them — to me, that’s the alarm,” said Vicki Blazer, fish biology researcher for the U.S. Geological Survey, and one of the report’s authors. “Obviously, humans are not going to be exposed in the same way fish are: We’re not constantly in the water, our drinking water is treated, but that doesn’t mean we’re not exposing ourselves to many of the same chemicals. To me, that’s the concern.”

Blazer identified several potential causes of Missisquoi River’s intersex fish, all of them resulting from agricultural practices.

James Ehlers, executive director of Lake Champlain International, said the abnormal sexual development of the small bass is “horrific.”

“I think they’re basically Franken-fish. It’s a canary in a coal mine, except it’s a bass in a river, and there’s something monstrously out of balance in the natural system.”

The intersex fish likely result from one or a combination of three substances, Blazer said.

An herbicide called atrazine is one possible cause, she said. Previous studies have shown that atrazine can trigger certain animals to develop traits of both sexes, she said.

Atrazine is the pesticide most commonly found in drinking water in the United States, and in 2012 a court case forced its manufacturer to pay over $100 million to filter the herbicide from a number of drinking water sources.

The European Union has banned the chemical’s use.

Confined animal feeding operations could also cause Missisquoi Bay’s bass to develop characteristics of both sexes, Blazer said.

Sometimes called “factory farms,” these facilities contain within relatively small spaces large numbers of animals for the purpose of cheaply producing meat and other animal products.

All animals naturally excrete hormones, Blazer said, and this type of farm produces especially high quantities of animal excretions.

Farms can also generate what are known as phytoestrogens, Blazer said. These molecules originate in plants and mimic estrogens produced by animals. Agriculture operations permit this substance to develop in sufficient concentrations to be thought to affect fish biology, Blazer said.

The cause of Missisquoi Bay’s egg-bearing male fish is probably one or all three of these, she said.

“The big thing to me is that we don’t truly understand the mix of things fish and other organisms are exposed to,” she said.

Agency of Agriculture representatives say they don’t intend to revise current practices in light of the study’s findings.

“The data in the study are in no way indicative of a need for regulatory change on herbicide applications in Vermont,” said Cary Giguere, Agrichemical Program Manager at the Agency of Agriculture. “We have no idea of the [intersex-causing pollutant] source. In some ways, the study shows proper management and protection.”

Giguere said that the study showed intersex fish even in waters where no agricultural or other pollutants could have entered the waters. Giguere also said that Vermont showed the lowest incidence of intersex fish of any state in the study. The study covered rivers in 10 northeastern states.

Vermont did have the lowest rate of intersex fish in the study, but 60 percent is nevertheless a worrying level of egg-bearing males in a fish species, said the study’s lead author, Luke Iwanowicz.

Even in the Chesapeake Bay watershed, fish are found with as low as a 10 percent rate of egg-bearing males, Iwanowicz said.

Egg-bearing male smallmouth bass at any level should be considered unnatural and indicative of harm to the species, Blazer said.

Although the study found intersex fish in waters unaffected by agriculture, a strong correlation exists between the intensity of agricultural practices and the prevalence and severity of intersex fish, Iwanowicz said.

“We always get in trouble if we try to say, ‘it’s only this, or only that,’” Iwanowicz said, “but with smallmouth bass especially, we’re very consistently finding [egg-bearing males] associated with agriculture.”

Iwanowicz said a compound found in the mouths of fish at higher concentrations in Missisquoi River than any other in the study might offer further evidence of this association.

Vitellogenin is a substance that indicates recent exposure to the estrogens that cause intersex fish, he said. Intersexuality is a trait caused by exposure to abnormal estrogen levels early in life, he said. That Missisquoi River fish have the lowest intersex rates but the highest vitellogenin frequency suggests that the source of intersex-causing estrogens is likely periodic, rather than constant.

This points toward a source like farm runoff, occurring during rain events, as opposed to the steady flow of effluent produced by sources like wastewater treatment plants, he said.

Farms in the Missisquoi Bay watershed have already been implicated as a source of the phosphorus that causes blue-green algae blooms in the bay, and Blazer said she hopes high-profile pollutants such as phosphorus don’t lead scientists, regulators and water users to overlook other pollutants such as those altering piscene sex traits.

Blazer said the phenomenon of intersex fish is assuredly a product of human activity.

Ehlers said he’s bent the ear of several legislators, some of whom have promised to consider the matter before the state’s lawmaking body.

House members have been made aware of the issue, and are currently scheduling hearings on the matter, Speaker Shap Smith’s chief of staff Dylan Giambatista said.

Mike Polhamus

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11 Comments on "Scientists say 60 percent of male Missisquoi fish bear eggs"


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Kathy Leonard
11 months 23 days ago

“Canary in a coal mine?” The canaries all died 50 years ago! We are not on the edge of anything, the verge of anything, the brink of anything,.. we are in the middle of it.

11 months 22 days ago

Kathy, perhaps you would like to get involved and help us then? If so, please contact me at james at Thank you.

mark Moye
11 months 22 days ago

Who actually published the report? A simple declarative statement such as ” The report was published by (insert name of organization./ individual). Vicki Blazer, fish biology researcher for the U.S. Geological Survey, and one of the report’s authors. WAS THE US GEOLOGICAL SURVEY the organization authorizing the study?

Jeremy Hansen
11 months 22 days ago

Here’s the reference:

Iwanowicz et al, “Evidence of estrogenic endocrine disruption in smallmouth and largemouth bass inhabiting Northeast U.S. national wildlife refuge waters: A reconnaissance study.” Ecotoxicology and Environmental Safety, Volume 124, February 2016, Pages 50-59, ISSN 0147-6513,

The two lead authors of the study are with USGS, and the remaining 14 are with various offices of US Fish & Wildlife.

James Maroney
11 months 22 days ago

In 1993, the legislature took responsibility for clean water away from ANR and gave it to the Agency of Agriculture. In the intervening twenty-two year period, water quality in Lake Champlain has gotten steadily worse. If one harbors any doubt that the agency’s first concern is not protecting water quality but shielding the conventional dairy industry from responsibility, one should again read the agency’s response to this study, which is denial followed by obstinacy.

Lea Terhune
11 months 20 days ago

That explains it! And this: Agency of Agriculture representatives say they don’t intend to revise current practices in light of the study’s findings.

bill mckibben
11 months 22 days ago

Why do state officials, confronted with 60% of male fish bearing eggs, say things like “In some ways, the study shows proper management and protection.” It seems guaranteed to come back and haunt you. This really is horrific.

Rowan Nelson
11 months 21 days ago

A simple moratorium on the three suspect farming practices (particularly the use of Atrazine) for a year should close the case. Breeding of bass and their relatively short lifecycle would allow a causal link to be demonstrated – unless the intersex trait is passed on to offspring, genetically. Such an alarming symptom of environmental pollution should be viewed as a crisis and not get mired in politics.

George Boomhower
11 months 20 days ago Last December Eric Lamontagne, of LCI, sent me a similar report about the intersex bass showing up in the Mississquoi. I answered with a rather frivilous, but not, note that I will repeat here: “Eric, This disruption may be already happening to the”next generation”, consider – – unisex bathrooms no big deal on college campuses today. What??? In my day, that would be a VERY BIG deal. Maybe the young guys are just more civilized today or maybe it’s the same syndrome that’s showing up in the small mouth bass population”. I hope the above web site can be… Read more »
Cameron Skinner
11 months 13 days ago
Hmmm… This seems to correlate to my personal experience a few years ago ice fishing in Missisquoi Bay on the Canadian side of the border. We caught around 20 perch and, being “The Fisherman” in the family I ended-up cleaning them all. At first I thought, well we sure caught a lot of females but, in the end we actually caught ALL females except for one fish. If I have my calculations close to right the probability of encountering such a ratio should be about 1/52000 assuming that there are equal numbers of male/female fish. Even if not, its pretty… Read more »
John Brabant
10 months 29 days ago
“The data in the study are in no way indicative of a need for regulatory change on herbicide applications in Vermont,” said Cary Giguere, Agrichemical Program Manager at the Agency of Agriculture. “We have no idea of the [intersex-causing pollutant] source. In some ways, the study shows proper management and protection.” These statements say it all folks. Such is the mentality and quite frankly, the legal rationale at our regulatory Agencies in Vermont and across our nation. It is up to us to prove harm, not the polluters. A large problem is that the chemical companies are protected in this… Read more »
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