found male fish that had female qualities in the Des Plaines River
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[May 07, 2016]
CHAMPAIGN - Largemouth bass males swimming in the lower
Des Plaines River below the Chicago metropolitan area showed female
characteristics at a high rate, according to a new study at the
Illinois Natural History Survey (INHS), Prairie Research Institute
(PRI), University of Illinois.
Scientists caught 51 male largemouth bass in spring, just before
spawning begins when intersex conditions, or the presence of
eggs in male testicular tissue, would be most observable. Of the
51 fish, 21, or 41 percent, showed intersex conditions.
This study may have implications for fishermen who enjoy the
sport and for those who consume fish from rivers with a history
of severe pollution, said Jason DeBoer, large river fisheries
ecologist at INHS.
Although the prevalence of intersex condition does not
necessarily indicate decreased fertility and reduced populations
of largemouth bass, it might foretell some negative effects.
Males with intersex conditions may have less mobile sperm,
fertilization of the eggs can be inhibited, or they are less
likely to protect their nest from predators.
“The presence of eggs in male testicular tissue can be caused by
chronic exposure to chemicals that are known to disrupt the
endocrine systems of animals among a number of other
physiological explanations, DeBoer said. “I don’t believe that
the reproductive success of the largemouth bass population has
been disrupted; there’s a very robust population in the river.
However, they are just not necessarily healthy.”
Findings also showed that 41 percent of the bass sampled
suffered from other physical impairments associated with
contaminated waters, such as parasites, fin erosion, black spot
disease, or infection from grubs in the internal organs.
These impairments may not be directly linked with the intersex
condition, and some conditions may occur in habitats not
affected by pollution.
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Exhaustive chemical analyses of surface waters and animal tissues
can be expensive and may not screen for all compounds in a river.
Therefore, intersex conditions in fish are a biomarker; an
indication of contaminant exposure and potential adverse effects.
The Des Plaines River, where the fish were captured, is downstream
of the greater Chicago Metropolitan area where discharge from sewer
overflow outlets, water from Lake Michigan, and effluents from seven
large water reclamation plants flow. Intersex conditions may be
caused by endocrine-disrupting chemicals from domestic, industrial,
and agricultural wastes, particularly from natural and synthetic
steroidal sex hormones.
[Lisa A. Sheppard]