[Pharmwaste] Lack of oxygen can mean more male fish in seas' dead zones

[Tenace, Laurie]

So, we just remove oxygen from the water where endocrine disruptors are
skewing the gender balance toward females and we've got this thing licked! -
Laurie 

http://www.sun-sentinel.com/news/local/southflorida/sfl-329malefish,0,3000153
.story?coll=sfla-home-headlines

WASHINGTON -- Scientists call the growing oxygen-starved patches of world
waterways "dead zones." That also could describe the not-so-swinging mating
scene for some of the fish that live there.

For zebrafish, low oxygen levels in the water turn their habitat into the
equivalent of a freshwater locker room. When oxygen is reduced, newly born
male zebrafish outnumber females 3-to-1, and the precious few females have
testosterone levels about twice as high as normal, according to a scientific
study released Wednesday.

Earlier studies also have found reproductive problems for males in other
species in oxygen-starved waters. And though all the research is conducted in
controlled laboratories, scientists say the gender bending is something that
could explain what they are seeing in the nearly 150 dead zones worldwide.

This could be a serious problem because with the expansion of dead zones --
such as the massive Gulf of Mexico area now the size of New Jersey -- fish
die, and those that don't die may not be able to keep the species alive,
scientists say.

Having too many males "is not a good strategy for survival," said Alan
Lewitus, who manages the dead zone program for National Oceanic and
Atmospheric Administration.

The world's dead zones add up to about 100,000 square miles and most of those
zones are man-made because of fertilizer and other farm run-off, said Robert
Diaz, a professor of marine sciences at the College of William and Mary. More
than 30 dead zones are in U.S. waters and are part of key fisheries.

The stress of hypoxia -- the lack of oxygen in water -- tinkers with the
genes that help make male and female sex hormones, said study lead author
Rudolf Wu, director of the Centre for Coastal Pollution and Conservation at
the City University of Hong Kong. Wu's peer-reviewed study will appear in the
May issue of the journal Environmental Science and Technology.

Wu restricted the oxygen of zebrafish, which are freshwater aquarium fish,
but said similar changes are possible in other species of fresh and saltwater
fish. Fish often change genders during their lives, but this is different, he
said.

"Since development of sex organs is modulated by sex hormones, hypoxia may
therefore affect sex determination and development," Wu wrote in an e-mail
interview. "Hypoxia covers a very large area worldwide, many areas and
species may be affected in a similar way."

Wu and others said oxygen starvation may be a more powerful sex
hormone-altering problem than the chemical pollution that has gotten
widespread attention.

In the Gulf of Mexico, sexual development problems have been found with
shrimp and croakers, said Nancy Rabalais, executive director of the Louisiana
Universities Marine Consortium.

The trend is worrisome, said Peter Thomas, professor of marine sciences at
the University of Texas.

"Hypoxia is emerging as a really important stressor, possibly of even greater
significance than chemicals," Thomas said. "When it does act, it shuts things
down completely." 


Laurie J. Tenace
Environmental Specialist
Florida Department of Environmental Protection
2600 Blair Stone Road, MS 4555
Tallahassee, Florida 32399-2400
PH: (850) 245-8759
FAX: (850) 245-8811
Laurie.Tenace at dep.state.fl.us  
 
view our mercury web pages at: 
http://www.dep.state.fl.us/waste/categories/mercury/default.htm 

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