Phyllis and Jim wrote:

Grass carp and walking catfish have been examples of foreign animals
wreaking havoc on North American ecosystems.

Neither one is a good example. Walking catfish have had fairly limited
effects, being established in Florida, but _everything_ is invasive in
Florida. They're not afaict established anywhere else.

Grass carp may have been established more widely but it's not clear from a
quick glance at the literature. They've been in the US since the early
60s, and there's no doubt they can denude an area of vegetation, but only
sterile carp are used intentionally, since the 80s. Those 200 lb-ers that
get caught are _old_ fish. Unlike Brown Gobies, it's pretty easy to find
Grass Carp.
--
derek