Colorado Division of Wildlife has issued an emergency order prohibiting the transport of live crayfish from Sanchez Reservoir State Wildlife Area following the discovery of invasive rusty crayfish at the popular southern Colorado reservoir.

An aggressive and invasive fresh-water crustacean, the rusty crayfish (Orconectes rusticus) has large claws and out-competes native species for food and habitat. They can clear large areas of aquatic plants, reducing habitat for invertebrates and shelter for small fish. They have a higher metabolic rate and appetite than other crayfish species and attain higher population densities.

Anglers collecting crayfish must either return them to the reservoir alive or immediately kill the crayfish by separating the crayfish's tail from the body, or thorax. Even crayfish harvested for human consumption must be killed by separating the edible tail from the body before leaving the reservoir.

source: Colorado Division of Wildlife

Mosquitofish are tiny freshwater fish that are native to North America. These small fish closely resemble dime store guppies, and like many aquarium fish, mosquitofish bear their young live rather than lay eggs.

In Australia, these tiny insect eating fish are considered to be an invasive species.
Still they are popular among aquarists and are stocked in garden ponds. Their popularity is related to their ability to control mosquitoes, their beauty and hardy nature. They are also important as forage for larger species of freshwater fish such as green sunfish.