[Pharmwaste] Soap chemical (4-nonylphenol) stops fish sticking together

[DeBiasi,Deborah]

http://environment.newscientist.com/article/dn12821-soap-chemical-stops-
fish-sticking-together.html

Soap chemical stops fish sticking together

00:01 24 October 2007 

NewScientist.com news service
 
Catherine Brahic 

 Fish form shoals to defend themselves against predators and to find
food faster.
A contaminant found in rivers and estuaries the world over can "rob"
fish of their ability to sense each other and stay in a tight, cohesive
shoal, say researchers.

The chemical, 4-nonylphenol, does this by overpowering the fish's
natural smell-signatures, say researchers. And because these signatures
are critical to helping the fish form in groups, the chemical
effectively weakens their "strength in numbers" defence against
predators.

"The loss of the ability to shoal cohesively is serious business for
fish. It's a defensive strategy. If fish can't shoal properly, they are
extremely vulnerable to predation," says Ashley Ward at the University
of Sydney, Australia, who led the study.

Nonylphenol or 4-NP is widely used in soaps, sewage treatment, and in
some pesticides. They are known to affect human and animal hormonal
systems, and can "feminise" fish, causing males to produce typically
female proteins.

In developed nations, the maximum concentration deemed "permissible" is
between 0.5 and 1 microgram per litre of water, because fish do not show
signs of stress at this level. In European rivers, typical
concentrations range from 0.1 to 340 micrograms per litre.

Keeping their distance
Ward and colleagues decided to test whether "permissible" levels of 4-NP
could disrupt social organisation in banded killifish, a shoaling fish
commonly found in North American lakes.

Ward - then a researcher at Mount Alison University in New Brunswick
province, Canada -gathered killifish from the nearby Morice Lake. He
found that the groups of fish that were placed in aquariums with 1
microgramme per litre of 4-NP tended to stay at least twice as far from
each other as those in uncontaminated aquariums.

The chemical did not appear to affect the fish's ability to smell other
substances, as they were just as able to find food hidden away in their
aquarium as the fish in the uncontaminated tanks.

Other experiments suggested that the reason the fish shoals were not as
tightly grouped in the presence of 4-NP was that the chemical was
masking the fish's own smell. "Shoaling fish develop a chemical profile
based on their recent habitat and diet - they smell of what they eat and
where they have been, just like us," explains Ward. "They prefer to
shoal with fish that smell similar to themselves."

Fish are also thought to produce chemical signals relating to their
social dominance, reproductive state, and genetic make-up. The last type
of signals help them avoid breeding with relatives.

'Sub-lethal' effects
But 4-NP is a lipophillic compound, meaning it tends to stick to oily
surfaces - a fish, for example. "It seems that it might 'coat' the
fish," says Ward. This changes their individual chemical signature and
breaks down recognition among the fish.

Ward and his colleagues placed single killifish in a corridor of water
that had two separate currents running down it. One current was clean.
The other came from a tank in which the researchers had placed killifish
that had previously bathed for an hour in 4-NP contaminated water.

The team found that the lone killifish moved away from the contaminated
current when the upstream fish had bathed in 4-NP at concentrations of 1
microgram per litre or higher.

"I think we need to reappraise our comfortable position that if a
certain concentration doesn't actually kill an animal, it's OK," Ward
told New Scientist. "There are subtle 'sub-lethal' effects that can be
devastating in the medium and long term."

Ward and his team point out that other chemicals, heavy metals for
example, damage the olfactory organs of fish. They say that in polluted
waters, chemicals like 4-NP and heavy metals could both be present, one
affecting the way that fish smell, the other their ability to smell.

Journal reference: Proceedings of the Royal Society B (DOI:
10.1098/rspb.2007.1283)


Deborah L. DeBiasi
Email:   dldebiasi at deq.virginia.gov
WEB site address:  www.deq.virginia.gov
Virginia Department of Environmental Quality
Office of Water Permit Programs
Industrial Pretreatment/Toxics Management Program
Mail:          P.O. Box 1105, Richmond, VA  23218 (NEW!)
Location:  629 E. Main Street, Richmond, VA  23219
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