CTV News has learned that Asian grass carp found in Lake Ontario during the summer were not born in the Great Lakes, suggesting the potentially invasive species is not breeding locally.

Becky Cudmore of the Department of Fisheries and Oceans lab in Burlington, Ont., said that oxygen levels and other chemical indicators in the ear bones of the fish captured near Toronto showed they are between 11 and 15 years old and were likely born at U.S. fish farms.

The carp -- which can grow to more than a metre long -- can be purchased for about $10 in the U.S. and are used in ponds and lakes to clear out vegetation.

The huge fish have no natural predators in North America waters, so they can quickly destroy delicate ecosystems.

Ontario banned the species in 2004, so the 11- to 15-year-old fish caught near Toronto were probably imported when it was still legal to do so.

Ontario Minister of Natural Resources Bill Mauro said the carp are still a concern, but that a new law passed earlier this month gives the ministry more powers to protect the environment from invasive species.

With a report from CTV Toronto’s Paul Bliss