Cray fish

Cray fish, crawfish, or crawdads are freshwater crustaceans resembling small lobsters, to which they are closely related. Pet crayfish are kept in freshwater aquariums, their disposition towards eating almost anything will also cause them to consume most aquarium plants in a fish tank.

Cray fish breathe through feather-like gills and are found in bodies of water that do not freeze to the bottom; they are also mostly found in brooks and streams where there is fresh water running, and which have shelter against predators. Most cray fish cannot tolerate polluted water, although some species such as the invasive Procambarus clarkii are more hardy. Some cray fish have been found living as much as 3 m (10 feet) underground.

In Australia and New Zealand, the name cray fish (or cray) generally refers to a saltwater spiny lobster, of the type Jasus that is indigenous to much of southern Oceania, whilst the freshwater species are usually considered a yabby, or a koura, from the Aboriginal, and Maori, names for the animal respectively. The study of cray fish is called astacology.

Crayfish tank
Pet crayfish prefer foods like shrimp pellets or various vegetables but will also eat tropical fish food, regular fish food, algae wafers, and even small fish that can be captured by their claws, such as goldfish or minnows. They are not suitable for planted aquarium since they consume most aquarium plants.  Pet crayfish need a hiding space that should be provided in crayfish tank since they are fairly shy and may attempt to hide under leaves or rocks. At night, some fish become less energetic and settle to the bottom. The cray fish might see this as a chance for an easy meal, or a threat, and injure or kill the fish with its claws. Cray fish are effective scavengers and will consume fish carcasses. They sometimes will consume an exoskeleton after it is molted. Since cray fish are accustomed to being around ponds or rivers they will have a tendency to shift gravel around on the bottom of the tank, creating mounds or trenches to emulate a burrow. Pet crayfish are great escape artists and will try to climb out of the crayfish tank, so any holes in the hood should be covered.

However, most species of dwarf cray fish, such as Cambarellus patzcuarensis will not destructively dig or eat live aquarium plants. They are also relatively non-aggressive and can even be kept safely with dwarf shrimp. Because of their very small size of 1.5 inches or less, some fish, such as loaches are often a threat to the pet crayfish rather than the other way around.

In some nations, such as England, United States, Australia, and New Zealand, imported alien cray fish are a danger to local rivers. The three species commonly imported to Europe from the Americas are Orconectes limosus, Pacifastacus leniusculus and Procambarus clarkii. Cray fish may spread into different bodies of water because specimens captured for pets in one river are often flung back into a different one. There is a potential for ecological damage when cray fish are introduced into non-native bodies of water.