A recent study in America has found that male fish may develop female characteristics in areas of increased agricultural activity.
Researchers at the National Fish Health Research Laboratory found increased levels of intersex in smallmouth bass (Micropterus dolomieu) in the Potomac River, Virginia.
Intersex is a condition where both sexual characteristics are found in one sex. In this example male bass were found to have oocytes or female germ cells in a male gonad- these are known as testicular oocytes.
Previously, incidences of intersex have been used in fish to indicate exposure to the female hormone oestrogen and its compounds.
However, this study found that in areas where there were relatively low population levels yet high levels of agriculture, that the levels of intersex were also high.
This suggests that agricultural runoff, wastewater effluents and poultry waste may be responsible for hormonal disruptions in fish.
Further studies of the water showed a number of chemicals known to be endocrine disruptors including herbicides, fungicides, several pesticides and even a flame retartdant.
Worryingly, in the same month a similar story has been in the news where Dr Karen Kidd from the Freshwater Institute in Canada reported that fish populations in Canada could potentially collapse due to high levels of oestrogen in municipal runoffs.
These hormones found in birth control pills and wastewater falls caused high levels of intersex in male fathead minnows (Pimephales promelas) and altered egg formation in females.
A seven year experiment on a lake in Ontario showed that chronic exposure to low levels of oestrogenic compounds resulted in the near extinction of these fish in the lake.
In further studies, researchers found traces of the anti-depressants Prozac and Zoloft in bull sharks in the US last month, potentially toxic levels of beauty products, pharmaceuticals, flame retardants and plastic additives in the Pacific Ocean off California. Analysis was even done to detect trace levels of Viagra.
Steven Bay a toxicologist is reported in the Los Angeles Times saying: The chemicals, appear to be working their way up the marine food chain," and many of them are "compounds known to mimic or disrupt hormones."
Of 30,000 chemicals used commercially in the USA and Canada, around 400 resist breaking down naturally and as such can potentially accumulate in fish and marine wildlife.
For more information see: ~Intersex (Testicular Oocytes) in Smallmouth Bass from the Potomac River and selected nearby drainages. Blazer,V, Iwanowicz, L and Iwanowicz, D. Journal of Aquatic Animal Health 19:242-253. 2007 DOI: 10:1577/H07-031.1