[Pharmwaste] Feminized male fish less likely to be fathers - research article

[Tenace, Laurie]

http://www.environmentalhealthnews.org/ehs/newscience/feminized-male-fish-less-likely-to-be-fathers/


Feminized male fish less likely to be fathers.


Male fish feminized by exposure to environmental estrogens do not father as many offspring as their normal counterparts, suggesting the changes may alter wild fish populations.


Male fish with a high degree of intersex produce fewer offspring when competing with normal males, according to a laboratory study that examined reproduction in intersex male fish - those with both male and female attributes.

Although much is known about intersex fish, little is understood about how the condition affects the number of fish in the wild. This is an important question because the consequences of intersex become even greater if it leads to declines in fish population size.

Prior studies hint that it does. In one study, a fathead minnow population in an lake in Ontario, Canada--where estrogen levels were manipulated experimentally--collapsed all the way to virtual local extinction when it was dosed with tiny (low parts per billion) amounts of the synthetic estrogen ethinylestradiol (EE2) for three years. A rise in the number of intersex fish in the minnow population was the first indicator of the impending collapse.

The results of the new study from the United Kingdom support the lake study and show that severe intersex conditions can reduce reproduction and may affect the genetic diversity of a fish population in rivers, too. The extent depends, however, on how many males are affected and the severity of the intersex problems.

A range of intersex conditions occurs, from mild to severe depending on the amount and kinds of characteristics present. Male fish that are intersex can have female reproductive tissues in their testes, make female yolk proteins and eggs, and can have lower sperm quality.

Intersex has been seen in fish from 86 percent of rivers in the United Kingdom. In the Potomac River Basin of the eastern United States, up to 75 percent of male smallmouth bass in certain locations show some degree of intersex. Treated sewage effluent containing estrogenic compounds (such as natural human or livestock estrogens or those in birth control pills) is one cause of intersex in aquatic environments.

Researchers collected wild roach - a type of fish common in English rivers - from two rivers at sites downstream from sewage treatment plants to learn if intersex male fish could effectively compete with normal males to father offspring.  They placed six males - a mix of wild-caught intersex and normal males - with three females in large tanks during two experiments:  one in 2006 with seven tanks, 38 male fish and 25 females; and one in 2008 with 13 tanks, 75 males and 42 females. Almost all of the male fish in the later experiment were more feminized than those in the first.

A week after spawning, the researchers collected the fish larvae and used DNA markers to identify the parents. The severity of intersex in the wild male fish was determined using a standard index that rates intersex by the number and extent of eggs in the testis tissues.

In both experiments, normal and intersex males of all severities participated in spawning and fathered offspring. However, intersex males produced fewer offspring - up to 76 percent less in the most impacted individuals. Within each tank, each normal male fathered an average of 19 percent of the offspring, while just 4.5 percent of the offspring were fathered by severely intersex males.

Like a canary in a coalmine, the rising number of intersex male fish in wild freshwater and ocean populations is a warning sign that environmental estrogens could fundamentally reduce genetic diversity and abundance of wild fish populations.




Laurie Tenace
Environmental Specialist
Waste Reduction Section
Florida Department of Environmental Protection
2600 Blair Stone Rd., MS 4555
Tallahassee FL 32399-2400
P: 850.245.8759
F: 850.245.8811
Laurie.Tenace at dep.state.fl.us

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