They can become exceptionally large, depending on the size of their new habitat. They can grow "exponentially," which leads to an increased appetite and forces them to become aggressive about maintaining the new diet, the study says.

When added with how difficult it is to eradicate the new fish, the problem seems to have long-term implications.

Exotic fish also pose the threat of spreading "exotic diseases and parasites, and can damage natural habitats," said Dr. Jeff Cosgrove, a river science environment officer.