Finned invader hits Lake Ontario
Plant-eating grass carp can destroy aquatic environments,
By Martin Mittelstaedt
The Globe and Mail
Biologists have discovered a grass carp, a dangerous invasive
fish originally from Eastern Asia, living in Lake Ontario
at the mouth of the Don River in Toronto.
The grass carp was caught inadvertently a few weeks ago
by staff at Toronto and Region Conservation during an
assessment of the size of fish communities in the Lower
Don River, one of the city's most polluted waterways.
Grass carp are feared because they are voracious feeders
of aquatic vegetation, an attribute that causes serious
disruption of any environment in which they become well
established. Their most destructive practice is ripping
underwater vegetation out by the roots, leading to increased
turbidity and poor water quality. They have become a major
pest in some areas of the United States, harming the commercial
and recreational fishing industry.
The pale grey fish, related to the common goldfish and
also known as the white amur, can become uncommonly large,
growing up to a metre in length and weighing up to 50
kilograms. It is something of a plant eating machine,
consuming up to its own body weight in vegetation each
day, giving it huge potential for disrupting underwater
Researchers from the Toronto conservation authority made
the discovery on Oct. 30 while they were electrofishing
-- passing an electric current through water -- to determine
the size and composition of the fish community in the
The electric current temporarily stuns all fish in the
immediate vicinity and makes them float to the surface.
Scientists can then easily gather them up in nets and
identify the species and their populations in a given
Scientists do not know yet whether the carp they caught
is a single fish released into the wild by someone in
the city, or if it is part of a previously unknown breeding
population around Toronto.
Live carp can be bought in fish markets, through the
aquarium trade and even over the Internet.
To try to solve this mystery, Toronto and Region Conservation,
the Ministry of Natural Resources and the federal Department
of Fisheries and Oceans are conducting what they call
an "aggressive" surveillance program on rivers
that lead into Lake Ontario to determine if there are
any more of the fish.
"The Ministry of Natural Resources is committed
to investigating this incident to confirm that this is
an isolated instance," Natural Resources Minister
David Ramsay said.
As long as the weather remains mild, researchers will
be conducting more electrofishing on the Don, Humber and
Rouge rivers this year. Additional electrofishing is planned
for next spring.
There have been only four known previous sightings of
grass carp in Ontario, and all of these were presumed
to be solitary individuals and not part of an established
breeding population. One fish was caught in Lake Erie
in 1985 and three more in commercial fishing nets in southern
Lake Huron during 1989 and 1998.
Grass carp were first brought to the United States in
the 1960s for research on the control of water plants,
but they subsequently escaped the research ponds.
They were introduced in Alberta in 1987 to see whether
they could keep irrigation canals clear of vegetation,
but they have since escaped into the wild. Many areas
in the U.S. and Alberta require that only sterile grass
carp be released, but despite this precaution, breeding
populations have become established in the U.S.
The fish caught in Toronto is being tested to determine
its age and whether it was capable of reproduction.
The Ministry of Natural Resources is asking the public
to report any sightings of grass carp, and wants fishermen
to keep samples of fish suspected of being grass carp
so they can be positively identified.