Looking exactly like freshwater lobsters, crayfish of one type or another are found throughout the world but are, strangely, missing from Africa. They range in size from minute forums to the giant Tasmanian crayfish (Astacophis franklini), which, at a body weight of over 7 pounds, is the world's largest species. Several types of crayfish are important food animals, and crayfish farms exist in many parts of the world, including the southeastern United States.

The first three leg pairs of the crayfish end in tiny claws, and with these the crayfish constantly probes about the substrate for food. The larger main claws are used to capture or dismantle large prey or are used in defense. The “tail” is hinged and, in times of danger, is thrust forward, creating a current of water that propels the crayfish backwards and out of harm's way. Crayfish are found in a wide variety of colors, with bright blue specimens occasionally available in the pet trade.

You will need to experiment to see which types of crayfish can be kept with other animals — some species do not spend much time chasing prey, preferring to scavenge, while others are acutely efficient predators and will also decimate aquarium plants. The appetites of most are quite easy to please, and all manner of plant and animal foods, including pelleted foods, flake foods, table scraps, and live foods are readily accepted. Crayfish are particularly efficient at removing food and black worms embedded in the substrate and are thus of great service as scavengers in the aquarium.

Crayfish make fascinating pets and allow us to view almost all of the activities that might normally occur in nature. All species are quite active and quickly lose their tendency to hide during the day. Many types, especially those with flattened bodies that dwell in rocky streams, are quite adept at rearranging their homes to their liking, and they will move surprising amounts of stones, gravel, and small rocks in their quest to create the perfect home. Their one drawback is their tendency to be aggressive toward each other, so be sure that they have plenty of room to avoid one another and that they have hideaways in which to retreat at shedding time. Like all crustaceans, their bodies will be soft for several hours after this process, leaving them unable to defend themselves against the attentions of their ever-hungry tank mates.

If you do choose to keep crayfish as pets, do not release any into areas to which they are not native. Introduced crayfish have become a serious problem in several parts of the United States and Europe. Breeding populations that result from the release of pets purchased as fishing bait, as well as escapees from crayfish farms, have depleted populations of native fish, crayfish, and aquatic plants.

Raised as food animals on crayfish farms in the southeastern part of the United States, especially in the state of Louisiana, this large (averaging 3 inches) crayfish makes a fascinating, if aggressive, aquarium pet. It becomes quite bold in captivity and will feed from the hand, but it cannot be trusted with aquatic plants or smaller animals. Some specimens are a brilliant red color and are quite attractive, and blue specimens are occasionally available as well. They breed quite readily in captivity, and the female carries the eggs attached to the swimmerets at the lower part of her body. Sweeping motions of these tiny organs serve to aerate the eggs. Newly hatched crayfish are replicas of their parents and after a time will leave the swimmerets to forage and then will return. At a certain point — and this seems to vary from individual to individual — the female will tire of her responsibilities and abruptly begin to consume the young that she has so aggressively defended. The best way to prevent this is to keep her in an aquarium stocked with rocky crevices and other shelters into which the young can retreat. You can also remove her once you see the young spending a good deal of time on their own — it is usually safe to dislodge the few crayfish that remain on her swimmerets at the time of her removal. You can raise the young together only if they are provided with a fairly large aquarium containing many hiding places, as they are cannibalistic.

Single crayfish make ideal inhabitants for unaerated goldfish bowls or other small containers. If kept in shallow water with access to the surface, they will get along quite well without aeration. In deeper bowls, the water should be changed every two or three days or aerated to provide oxygen.