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There are over 200 species of crayfish in North America, and several species are available from biological suppliers (see crawdad.cornell.edu). We strongly recommend Procambarus clarkii for these labs. This species is cultured for food in Louisiana and normally lives in warm stagnant water. Thus it is easy to care for, since it does not require running, cooled, or aerated water. It also seems to be hardier as a dissected preparation, perhaps because of its tolerance for low oxygen. Some suppliers offer different sizes of crayfish; large ones are slightly more expensive but worth it because they are easier to use.
Keep crayfish in a closed container in water about an inch deep. Crayfish are territorial and cannibalistic and should not be crowded. They will do better if you provide hiding places such as broken clay flowerpots or 6- to 8-inch lengths of 3- to 4-inch diameter PVC pipe. For the duration of a lab course, they will survive on carrot pieces; if they are to be kept longer, they should also be fed dry cat or dog food. Every 2 to 3 days, remove any dead crayfish, replace the carrots, and change the water when it becomes foul. Crayfish do best in tap water that has been left sitting for several days to remove chlorine. Do not use distilled or deionized water, which lack minerals the crayfish need. If water is required immediately, bottled spring water can be used.
For crayfish, cold is an effective anesthetic. Simply place the crayfish in the freezer or bury it in ice and leave it until it stops moving. If using ice, note that the crayfish will get cold faster in ice water than in plain ice. After cutting off the tail, place the head in the freezer to die. Although the brain dies quickly from anoxia after the tail is removed, the thoracic ganglia live somewhat longer and continue to move the appendages. You may want to point out to students that because the crayfish does not regulate its body temperature, cooling slows all metabolic processes, including the neural processes involved in perception and movement.
Many students are rightly concerned about the welfare of the animals they use and about the environmental impact of collecting animals in the wild for lab use. Although it is impossible to know whether crayfish experience damage in the same way that we do, they clearly lack the brain organization that underlies our experience of pain and the emotional distress that goes with it. Since Procambarus is raised in large numbers for food, its use in lab exercises has minimal environmental impact. Unused crayfish should not be released at the end of a course, due to potential ecological disruption.