Crawfish are a major problem here in Arizona, pushing out alot of native
species. I've done research on native fish and learned that crawfish will
eat algae, plants, fish, baby ducks (!), frogs, poisonous toads, any egg,
and other crayfish. They are extremely aggressive, and can get very big.
Crawfish like to dig in their search for food, so they will uproot many
plants.

good luck
--donovan