As omnivores, Crayfish like to eat shell fish, worms, plants, insects, plankton, insects and snails. Crayfish are not picky and will even eat dead fish, decaying plants and dead animals. They will eat anything within their reach, whether it be in the wild or in the bottom of their tank.
If you have a fish tank with crayfish in it, you may want be cautious about adding other small fish to the tank. Drowsy fish or fish that swim on the bottom of the tank make easy meals for crayfish. Crayfish love to eat decaying plants such as spinach and lettuce, and will eat it immediately if available. Gold fish food, Algae wafers and shrimp pellets are all nutritious foods that you can buy in a pet store for your crayfish.
In the wild, crayfish tend to go after rotting plant matter, dead fish and other things that are easier for them to catch. They have been known to eat small rodents and birds if they can get their pincers on them. They eat their own shell when they moult in order to recover calcium. If put in an aquarium with other fish, plants and other aquatic creatures, crayfish will attempt to eat anything they can catch.