Animals In Print
The On-Line Newsletter
From 12 April 2008 Issue
Research by Iqbal Khan
Latest Scientific studies have taken a new turn towards marine life. These studies are showing results related to male fish developing characters like female fish. The main cause of this settlement of characters in the opposite sex is pollution. It is now believed that waste chemicals which make their
turn towards the aquatic world are the major cause of this very problem.
Hundreds of widely used man-made chemicals -- including pesticides, industrial compounds, dioxins and ingredients of plastics and detergents -- are believed to mimic estrogen or block testosterone, disrupting the endocrine system that is critical to sexual development.
Other recent studies had found scattered populations of animals with sexual defects living in highly polluted waters, but the new research suggests that the problems are more widespread than previously detected. The British researchers said they uncovered "very compelling evidence" that sewage-treatment plants routinely release hormone like compounds into rivers that are feminizing "a surprisingly large proportion" of wild fish. The incidence and severity of inter-sexuality . . . is both alarming and intriguing.
This study is now being widespread in Great Britain where all the eight rivers are facing this fish feminization. Some male fish have such mixed-up hormones that they are born with ovaries and eggs instead of sperm ducts. In two of the eight rivers downstream of sewage-treatment plants, all of the male fish sampled had feminized reproductive tracts. The other six rivers had rates from 20 percent to 80 percent. So scientists suspect damage to sex hormones is so pervasive that it could be happening in many rivers around the world. Hormonal havoc, however, has previously been reported in alligators, birds, river otters, carp and other wildlife in isolated locations.
Adult animals are unharmed by hormone-imitating pollutants. The damage is done to the next generation. Mothers pass the excessive amounts of estrogen to their embryos or fetuses, which cannot distinguish between fake estrogens and real ones. When this estrogen boost comes during a critical phase of sexual development, genetic signals go haywire and males are born with feminized genitalia or other reproductive problems. Both in vitro assays and in vivo approaches have been developed to evaluate estrogenic effects of these toxicants. The occurrence of the female specific egg yolk precursor protein vitellogenin (Vtg) in the plasma of male fish has widely been used as an indicator or biomarker of xenoestrogen exposure Hormones play the same vital sexual role in humans as they do in fish and other animals. Although people are exposed through food and water to the same pollutants as water-inhabiting animals, they encounter much lower doses, so any effects on humans may be subtle.
Scientists wonder how minute concentrations of fake hormones in the environment - which are hundreds of times less potent than natural estrogen - could have such a severe impact. They do not know which chemicals are to blame, since sewage is everything that is washed down drains.
The culprits could be anything from the urine of women excreting artificial hormones from birth-control pills, to pesticides or plastics. Evidence is emerging that wildlife is being feminized in waters where modern environmental practices and laws are followed and the ecosystem appears
The reproductive damage might have dire consequences for an ecosystem, because if males are sterile, an entire animal population might gradually be depleted. Fish, in particular, are an important link in the world's food chain.
"What we still don't know is if these inter-sex fish are reproductive or not. That's the bottom line, some of them have no sperm ducts, so obviously they can't reproduce.
Because females are more critical to reproduction than males, populations can regenerate themselves even if only a few males are fertile. Over the generations, though, if feminization remains unchecked, fisheries could collapse.
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