Crayfish use their gills to breathe. A crayfish has a gill at the base of each leg. These gills are very delicate and are covered by the crayfish's carapace, or shield. This carapace is aligned backwards from the head, allowing water to run through in a channel over the gills, which provides a continuous source of oxygen that allows the crayfish to breathe.

Crayfish are crustaceans that are a part of the phylum Arthropoda. These insect-like creatures are characterized by a hard outer shell and multiple legs. Crustaceans are unique from other members of the phylum Arthropoda due to their dual sets of antennae. One set is an outer pair that is called antennae. The second set is an inner set that is called antennules. A crayfish's body has three distinct parts: a head, thorax and abdomen. The abdomen section contains the tail, which is the edible part of many crustaceans, including crayfish. The crayfish's legs and gills are contained in the thorax region of the body. Australia boasts both the largest and smallest species of crayfish in the world; crayfish are also native to the continent. Crayfish are considered freshwater invertebrates. They prefer to live in streams, rivers, lakes and swamps and are nocturnal creatures, preferring to search for food at night.