Urban fish masculinized by hormone-mimicking chemicals

Sep 26, 2013
Endocrine disrupting chemicals are known to cause physiological and behavioral abnormalities in fish. Credit: Susanne M. Brander

(Phys.org) —It's a man's world for fish in a San Francisco Bay-Delta estuary. Silverside fish collected from an urban beach in Suisun Marsh were more masculinized, but with smaller and less healthy gonads, than were neighboring silversides swimming near a cattle ranch in the marsh, according to a new study led by the University of California, Davis.

The study, published Sept. 25 in the journal PLOS ONE, measured the effects of , which mimic hormones, on Mississippi silversides (Menidia audens) at the two beaches.

Endocrine disrupting chemicals are known to cause physiological and in . They come from a variety of sources, such as agricultural, urban and residential run-off. They're also found in wastewater effluent, which includes pharmaceuticals such as birth control, and some anti-inflammatory medications known to contain endocrine disruptors.

"The DNA sequence for a in a fish isn't that different from the DNA sequence for a hormone receptor in a human," said lead author Susanne Brander, who was a doctoral student at the UC Davis Bodega Marine Laboratory when the study was conducted. She is currently an assistant professor at the University of North Carolina, Wilmington. "Exposure pathways are different, of course, but what we see happening with fish is indicative of potential issues that could cause problems with human health. We're not swimming around in a soup of hormones and pesticides, but we're exposed to those things through food or in the air."

The researchers analyzed the fishes' response to endocrine disruptors at the molecular, cellular, organism and population levels to better predict the ecological impacts of such exposure. For example, would an abnormality at the cellular level indicate abnormalities for the whole population?

The ranch beach was less polluted than the urban beach, with ranch run-off being the primary source of pollution. The study found that male fish at the ranch beach had a higher expression of genes normally only expressed in females, compared to their male counterparts at the urban site. Yet, this did not appear to affect the sex ratio or gonadal health of fish at the ranch site, which was roughly 50-50 male and female.

However, males dominated at the urban beach, which was exposed to several sources of pollution—a nearby wastewater treatment plant, the surrounding urban community, as well as ranch lands. The males had smaller, less healthy gonads relative to their size, indicating that they might produce less sperm than male fish at the ranch site. Fish at the urban site also grew more slowly than the ranch fish. And while female silverside fish are typically larger than males, males at the urban beach were larger than both the urban females and the ranch males.

A potential explanation, the researchers hypothesize, is that exposure to androgens—hormones like testosterone that control the development of male characteristics—reduced the expression of estrogen-dependent genes, which the females need to develop and reproduce successfully. Androgen exposure from endocrine disruptors may also be causing some of the fish that would have been female to become male, Branden said, adding that ongoing research is working toward investigating that hypothesis.

The study also found that the Mississippi silverside appears to be a good indicator species for studying the effects of endocrine disruptors. Researching the impacts of these chemicals in the San Francisco Bay estuary has been challenging for scientists because many of the region's highly impacted native species cannot be collected in large enough numbers to study. However, the Mississippi silverside, introduced in the early 1970s to the estuary, shares similar habitat, diet and lifespans with some endangered fishes.

"A lot of endocrine disruptor work has been done with fish such as Japanese medaka and zebrafish, but you can't go out and catch those in the San Francisco Bay," Brander said. "The Mississippi silverside is a fish that can be used both for studying ecotoxicity in the wild and translating that to what's happening in the lab."

Explore further: Ants in space find it tougher going than those on Earth

More information: dx.plos.org/10.1371/journal.pone.0074251

Related Stories

Are there drugs in our water?

Sep 16, 2013

Recreational drugs could become a major source of Australian urban water contamination, scientists warn.

Guppies lie about mate choice to trick rivals

Sep 09, 2013

When it comes to sex among guppies, competition is high for those at the top of the game. To get around this predicament, a recent study has shown, guppies use trickery. ...

Recommended for you

Scientists discover new 'transformer frog' in Ecuador

5 hours ago

It doesn't turn into Prince Charming, but a new species of frog discovered in Ecuador has earned the nickname "transformer frog" for its ability to change its skin from spiny to smooth in five minutes.

US gives threatened status to northern long-eared bat

8 hours ago

The federal government said Wednesday that it is listing the northern long-eared bat as threatened, giving new protections to a species that has been nearly wiped out in some areas by the spread of a fungal ...

Mice sing like songbirds to woo mates

8 hours ago

Male mice sing surprisingly complex songs to seduce females, sort of like songbirds, according to a new Duke study appearing April 1 in the Frontiers of Behavioral Neuroscience.

A new crustacean species found in Galicia

9 hours ago

One reason that tourists are attracted to Galicia is for its food. The town of O Grove (Pontevedra) is well known for its Seafood Festival and the Spider Crab Festival. A group of researchers from the University ...

Ants in space find it tougher going than those on Earth

10 hours ago

(Phys.org)—The results of a study conducted to see how well ants carry out their search activities in space are in, and the team that sent them there has written and published the results in the journal ...

Rats found able to recognize pain in other rat faces

11 hours ago

(Phys.org)—A team of researchers working in Japan with affiliations to several institutions in that country, has found that lab rats are able to recognize pain in the faces of other rats and avoid them ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.