Although they don’t get much media attention as an invasive species, goldfish are reproducing by leaps and bounds in a number of North American waters. (Not to be confused with common carp, which can be gold in color as well, goldfish have no barbels on the upper jaw.)
It’s thought that people wishing to be rid of them flush live goldfish down the toilet or dump the fish into nearby ponds, lakes or streams.
|Martin and goldfish - medicaldaily.com|
[Goldfish] are able to tolerate fluctuations in water temperature and water with low levels of dissolved oxygen. They feed mainly on fish eggs, larvae and aquatic plants. In healthy ecosystems, goldfish don't appear to compete well with some native fish. However, they are quite tolerant of poor water quality, and may threaten some native species in degraded ecosystems.
Occasionally, a large goldfish caught by someone fishing will be reported as a curiosity in the press. Such was the case two years ago when Mike Martin caught a 15 inch, three pound goldfish in Lake St. Clair. Similar catches have been reported in the Saginaw River and Saginaw Bay.
But the concern is that large populations of goldfish will have a negative impact on aquatic ecology.
Jeanna Bryner wrote in Live Science on April 9, 2015:
Apparently, a handful of goldfish dumped into a lake in Boulder, Colorado, just three years ago have reproduced and now number in the thousands.
A ranger noticed the 3,000 to 4,000 goldfish a couple of weeks ago in Teller Lake #5 off Arapahoe Road and reported it to [authorities].
"If they escape and move downstream, they'll directly compete with our native species...“
There are about three or four fish species considered threatened or “species of concern” living downstream from the lake...These fish feed on plankton and small insects, the same diet as goldfish…
Closer to home, the harbor at Hamilton, Ontario on the western end of Lake Ontario is being overrun with goldfish. On January 7, 2016, Mark McNeil reported in the Hamilton Spectator:
It used to be that goldfish in the Ontario outdoors had a very low survival rate and little success at reproducing.
But officials at the Royal Botanical Gardens and the Department of Fisheries and Oceans Canada say that's been changing in recent years in the warmer weather we've been experiencing.
They've noticed exponential increases in numbers being counted at the Desjardins Canal Fishway — from 20 or less per year in the late 1990s to 2,500 this past spring. And early this winter, millions of five centimetre, young-of-the-year goldfish have been seen swimming in giant schools at various locations in the harbour, including the section of the canal below the railway bridge.
The Ohio Department of Natural Resources says:
Goldfish were first introduced into Ohio around 1885 but have not become as well established as the common carp. They are abundant in the shallow bays and marshes of western Lake Erie and can be found in slow moving tributaries of Lake Erie as well.
No explanation has been found for the rapid increase of goldfish reproduction in western Lake Ontario, compared to the (apparent) more stable population in western Lake Erie. Possibly the water quality at Hamilton, Ont. has degraded to the point that other fish species are declining, allowing the more tolerant goldfish to thrive.
In 1920, a phenomenon more extreme than that in Hamilton occurred in Port Clinton, Ohio. That incident hasn’t been explained either.In any case, the potential danger of further disruption to the balance (if there is one) in western Lake Erie bears watching.