Dead zones leave fish less virile

Sept. 12, 2007

From Proceedings of the Royal Society of London

http://pubs.acs.org/subscribe/journals/esthag-w/2007/sept/science/rc_hypoxia.html

Fish that survive low-oxygen water may suffer from reproductive problems.

It is no surprise that a dip in oxygen levels in water can kill fish, as
has occurred in the Gulf of Mexico's notorious dead zone. But as new
research published online on August 28 in Proceedings of the
http://journals.royalsociety.org/content/j42171g561475pr5/?p=00ef0e44ea1f49b880848349b1453b00&pi=0Royal Society of London, Series B shows, fish from the hypoxic coastal
waters of Florida produce fewer eggs and less sperm, which can affect
survival of the species.

Previous research by Rudolf Wu of the City University of Hong http://pubs.acs.org/subscribe/journals/esthag-w/2003/mar/science/os_fish.html
Kong suggested a potential link between hypoxia and endocrine function.
In laboratory experiments, his group showed that reduced oxygen levels
disrupted the development of ovaries and testes in adult carp. The group
also reported that hypoxia masculinizes lab-bred female zebra fish,
http://pubs.acs.org/subscribe/journals/esthag-w/2006/mar/science/jp_deadzones.html 
but effects on wild fish populations remained unknown.

In the present study, http://www.utexas.edu/research/eureka/faculty/view.php?pid=281 Peter Thomas and his colleagues at the http://www.utmsi.utexas.edu/ Marine
Sciences Institute of the University of Texas Austin looked at the
reproductive system of the Atlantic croaker-a species that can tolerate
moderate reductions in oxygen levels. Fish from low-oxygen areas of
Pensacola Bay had significantly smaller ovaries and testes and produced
fewer eggs and less sperm than those from nearby waters with normal
oxygen levels. The researchers also observed similar effects in wild
croakers exposed to hypoxic conditions in the lab. Further experiments
showed that these changes are caused by reductions in the levels of the
neurotransmitter serotonin, which controls the synthesis and release of
sex hormones.

This is the "first clear evidence" that low oxygen levels can affect
endocrine function and reproductive health in wild fish populations,
says study coauthor Md. Saydur Rahman. Understanding these effects is
important, he says, because intensified agricultural practices around
the world are increasing the number of dead zones. "We will be
estimating the long term effects (on fish population) by using the
information as inputs into a population model," says Thomas. -RHITU
CHATTERJEE http://pubs.acs.org/journals/esthag/bios.html