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Why Files:

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Environmental Hormones

Fish fauna

I thought YOU brought the charcoal! University of Idaho zoologist James Nagler with chinook salmon carcasses on the shore of the Columbia River. He clipped samples from fins in November 1999 and again in fall, 2000. No word on who got to broil the salmon steaks. Courtesy University of Idaho

A portrait of the chinook.
Courtesy Pacific Northwest National Laboratory

POSTED 5 JANUARY 2001 Male salmon near a giant nuclear installation on the Columbia River have changed into females -- and radiation is not to blame, according to a new report. In 1999, 84 percent of female chinook salmon spawning in a stretch of the Columbia in the Hanford Nuclear began life as males!

The "female" fish carried a Y chromosome, a sure marker of maleness in normal chinooks -- and monkeys, mice and men, for that matter. Fluctuating water temperatures and hormone-like pollutants in the water may be causing the oddity.

Scientists have known for decades that changes in temperature can cause embryonic reptiles to change sex, says James Nagler, assistant professor of zoology at the University of Idaho, who lead the research. Within the past five years, it's become clear that fish had similar flexibility, so when a simple test kit for genetic maleness in salmon became available, he decided to use it.

Populations of the Northwest's fashionable fish are plunging, for multiple and controversial reasons related to logging, dam building, agriculture and urban development.

Ironically, Nagler chose to study a population of chinook salmon that is relatively healthy, in a stretch called the Hanford Reach that's four dams upriver from the Pacific Ocean.

Since Nagler expected to find genetically male fish looking, well, male, he found the results odd. The high incidence of sex-reversed fish "was really a surprise to us," he says. "We didn't expect it, there was no precedent for this in chinook salmon."

Indeed, while 84 percent of sampled females began life as males, the actual number could be higher, since the Columbia receives a large number of hatchery fish to compensate for those decimated by dams. (Fish from Priest Rapids hatchery, which are genetically identical to wild river fish in Hanford Reach, and served as controls for the experiment. Nagler says the sex reversal does not appear among hatchery fish, perhaps because they live in water taken from wells, not the river.)

How come?
Given the proximity of the plutonium-separation operations at the Hanford Site, where rusty, leaking storage tanks hold toxic, post-nuclear soup, radiation was an early candidate for blame. "The levels were low," says Nagler, "and there's simply no scientific precedent that low levels of radiation could cause these kind of changes in fish."

A more likely suspect is the 2- to 6-degree Celsius fluctuation in water temperature, caused by the Priest Rapids dam, which regulates water flow. "There's a huge literature in reptiles about temperature-dependent sex changes in the wild," says Nagler. "In a hot year, there are more males, in a cold year, more females."

Causation-wise, the other hot prospect is environmental hormone mimics, trace chemicals that act like estrogenic hormones, distorting reproduction, development, and sexual characteristics. These so-called hormone disrupters include several widespread industrial and agricultural chemicals, yet Nagler says concentrations in the Columbia are far below the level that causes sex reversals in the laboratory. However, since many chemicals mimic hormones to some degree, an unmeasured hormone mimic could be responsible.

Implications
Equally unclear is what it all means. Though they sound vaguely threatening, like some fraternity prank run amok, sex-reversed fish can survive and reproduce in lab tanks, producing males with two Y chromosomes -- real freaks of nature. While nobody has yet sought these Double-Y fish in the Columbia, Nagler says they might produce all-male offspring. If that happened, the population of salmon looking to reproduce in the river might start to resemble a boy's boarding school. And as any boarding-school graduate will attest, sexual purity is not the swiftest route to species survival.

And while research is expanding -- hatchery fish will, for example, be raised in river water -- Nagler insists that the results do not yet explain the widespread decline of salmon in the Northwest: "It's premature to say that this is a even a minor player" in the ongoing problem.

Until it's clear whether sex reversals are affecting a high proportion of fish year after year, "I'd not want to speculate. It's a possibility that this is one factor among many factors."

-- David Tenenbaum

Bibliography:
High Incidence of a Male-Specific Genetic Marker in Phenotypic Female chinook Salmon from the Columbia River, James J. Nagler et al, Environmental Health Perspectives Volume 109, Number 1, January 2001.
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