Crayfish, also known as crawfish, crawdads, freshwater lobsters, or mudbugs, are freshwater crustaceans resembling small lobsters, to which they are related; taxonomically, they are members of the superfamilies Astacoidea and Parastacoidea.They breathe through feather-like gills and are found in bodies of water.n the Eastern United States, crayfish is more common in the north, while crawdad is heard more in central and southwestern regions, and crawfish further south, although there are considerable overlaps. The study of crayfish is called astacology.