Identify this fish??

[unirdna]

That's a mottled sculpin (Cottus bairdi). They are found mostly in trout streams, but can handle almost any water that is 72 deg or colder. I've kept them in aquariums that eventually hit 78 deg, but they were acclimated to this temp over several weeks. They are indigenous and pose no threat to native fishes, but yes, given the right water conditions (and few predators), they will multiply like rabbits. Or, actually, one should say that rabbits multiply like sculpin. In the great lakes, the burbot feast on them.