Scientists who reported discovering feminized fish in the Pacific Ocean off Southern California now say the findings were based erroneously on samples accidentally contaminated by researchers.

The 2005 discovery received worldwide attention because it was the first and only time that intersex animals – a phenomenon when males exposed to hormone-like pollutants have ovary-like testes that grow eggs – were found in the ocean. At the time, the half-male, half-female flatfish were linked to massive sewage outfalls off Los Angeles and Orange counties.

But when scientists at the Southern California Coastal Water Research Project returned to the same locations to test several hundred more fish, they didn’t find any egg-growing males. So last November they retested the original fish samples, and reread the pathology report, and realized that the eggs found on the males were not actually inside their testes.

Steven Bay, head toxicologist at the government-funded research institution, said they apparently were “stray eggs.” Some of the females’ eggs apparently dropped onto the male fish tissues. Bay said he is unsure whether the cross-contamination occurred on the boat, where the turbot and sole were collected and dissected off Los Angeles, Palos Verdes Peninsula and Huntington Beach, or in the laboratory.

“What happened, when we interpreted the report, we weren’t careful in reading the pathologist’s words,” Bay said. “The problem was in my group not interpreting the report with as much caution as they should have. The hints were there.”

Other scientists who do similar work with fish said they were surprised by the mistake. It’s a sign that the tissue dissection or processing, perhaps most likely in the field, was “sloppy.”

“If the knife was not cleaned between samples and people were sloppy then they may have contaminated the testes samples. I guess the best thing to do in this situation is to accept that this is what happened. Very unfortunate,” said Karen Kidd, a biology professor and Canada Research Chair at University of New Brunswick who researches hormone disruption in freshwater fish.

Emerging over the past 20 years, research that connects hormone-mimicking pollutants to feminizing effects in wildlife and people around the world has been highly controversial.

Joseph Gully, supervising environmental scientist at the Los Angeles County Sanitation Districts, called the mistake “a bit of a disaster.”

Gully said the false feminized fish “triggered a lot of concern and a lot of effort” by the local sewage agencies, which were so worried that they funded a $750,000 follow-up study of 600 more fish in 2006. “We couldn’t figure out why [intersex fish] were there one year and not the next. It is somewhat encouraging that we don’t have the results we first thought we had.”

Altered hormones in ocean fish
Despite the error, the Southern California scientists said their new peer-reviewed, published research confirms that bottom-dwelling ocean fish are highly exposed to hormone-disrupting chemicals off Los Angeles and Orange counties. Other more subtle signs of altered hormones were confirmed – including reduced estrogen levels in male turbot near the sites where wastewater is discharged.

Every day, billions of gallons of treated sewage from the two counties are discharged into the ocean via three outfalls, or ocean pipelines, that extend two to five miles offshore. The discharge includes women’s natural estrogen as well as manmade, hormone-like substances from birth control pills and consumer products.

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