We have had many, many discussions of crawfish (crayfish, etc.) in previous years. Octopuses seem to love them, but, being freshwater, the conclusion was to use them as a treat, not as a basic food.
It's hard to find suitable ones - the females have small claws while some of the big males look like marine lobsters with huge claws! During crawfish season, they can be found in stores carrying Mexican food, and also in seafood stores. Most crawfish we see in stores are not wild, but farm raised and sometimes seem half dead by the time they are sold.
They can live in salt water only a few hours. To make sure my bimac would catch them right away, I got her attention, and they held up the crawfish outside of the tank so she could see it. She got very animated at the sight. I had her wait on one side of the tank, then I freed the crawfish in front of her, and she chased it and caught it. She was always enthusiastic about crawfish.
Nancy