Article overlooks chemical’s role in determining fish sex.

Posted by Tamara Tal at Jan 19, 2012 08:00 AM |

Lisa Abend’s timely web article for Time Magazine illuminates an intriguing – yet sobering – study that details how warmer water pushes fish populations to be dominated by males. A 3 to 4 percent water temperature increase triggered 80 percent of the fish offspring to develop as males compared with normal sex profiles of roughly 50 percent male and 50 percent female. The sex of individuals in many species of fish and reptiles is determined by a wide range of environmental factors during development, including temperature.

The author does a lovely job of explaining how elevated water temperatures churn out more males. A gene that drives female sex determination by cutting off estrogen production is silenced by an epigenetic mechanism.

Even so, she misses an additional critical point: It’s well accepted that chemicals in the environment can also abnormally skew sexual differentiation.

Laboratory studies have shown that the boat and ship antifouling agent tributyltin – well known to cause masculinization of female mussels – can also skew fish sex ratios toward males at very low levels. Interestingly, concurrent exposure to low levels of a synthetic estrogen can overwhelmingly reverse the masculinizing effects of tributyltin. Many countries have restricted or banned the use of anti-fouling paints that contain tributyltin as a result of its toxic effects on shellfish.

Also, a 2002 study reported that populations of eelpout near a large Kraft pulp mill that discharged waste effluents into the water stream had a male sex bias two years in a row while other sites had stable sex ratios. When the mill temporarily closed down during the time of year that eel sexual development occurs, the sex ratios returned to the normal 50/50 ratio in year three of the study. The following year, the mill resumed its activities and abnormally large amounts of male eels turned up again. Another research group identified increased levels of androgenic chemicals in pulp effluent as the possible culprit behind the observed male bias.

In the case of effluent from wastewater treatment facilities, the reverse may be true. Wastewater effluent has been associated with increased rates of feminized fish, which may arise from higher than normal levels in the water of chemicals that have antiandrogen effects.

Together, these studies point to a subset of environmental chemicals that – like increasing water temperature – may abnormally skew fish sex ratios.

The environmental and ecological effects of global climate change are certainly cause for concern. Indeed, these insults act as a "thousand cuts" to fish species, notes Oregon State biologist Scott Heppell in the article. The pervasive presence of chemicals in the environment and their role on organisms and population biology is another important potential "cut" to the health of wild fish populations and as such deserves our attention.

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