Crayfish Basics By Justin Pierce Many people associate crayfish with their youth. Mention the word “crayfish” and people respond with something like “oh ya, I used to catch them down at the creek when I was a kid”.



However the hobby of keeping crayfish in captivity has been rampantly growing in popularity among people of all ages. Being able to observe them in an aquarium fosters appreciation beyond the simple childhood curiosity. This is especially true in Japan and some European countries where they have been quite en vogue for decades. The United States usually plays catch-up with aquarium trends, and is following suit with its own crayfish craze. Crayfish are becoming more commonly seen for sale in aquarium stores and in Internet auctions and websites.



This gain in popularity comes at no surprise to the people that are familiar with crays. Once exposed to their interesting behaviors, individual personalities and attractive colors and patterns people often develop the extreme fascination that borders on obsession, similar to many other aquarium genres. I thought I would take a moment to write an article that covers the very basics of keeping crayfish. This should give all those people interested in becoming involved with crayfish a foundation on what it takes to do so.

Hopefully you will see that they are very easy to care for, which is one of the endearing qualities making them so popular.



Housing



Crayfish are among the least demanding animals kept as pets, making them suitable for both children and adults. Compared to other aquatic and semi-aquatic animals, they only require the simplest living conditions, with filters and air pumps being optional extras rather than essential pieces of kit. That said, most people keep crayfish in a typical aquarium-type set up that includes a filter, and if you choose to keep your crayfish this way, so much the better. But at the bare minimum all you need for a crayfish enclosure is a small body of fresh water deep enough to cover the animal completely, and a rock or branch that allows it to climb out of the water (without being able to escape, of course!). Note that being able to climb out of the water is an essential requirement if the water is not aerated or filtered; crayfish need lots of oxygen, and in still water conditions, such as in a tank without a filter or airstone, they will get the oxygen they need from the air. But if they can’t climb out of the water easily, they will effectively drown.



Crayfish do not need to be kept a true aquarium, although this provides the best viewing of these creatures. The container can be as simple as a 5-gallon bucket or a plastic shoebox. Just make sure that the rim of whatever container you use is taller than the crayfish is long: they are amazing escape artists! If the container is not tall enough, they will probably need a vented lid to keep them contained. Crayfish are capable of climbing air hoses or anything else that extends high enough for them to reach the top.



Most crayfish burrow to some extent, whether a full-blown tunnel with complex chambers dug into the mud or simply a depression excavated underneath a submerged rock or branch. In captivity they will feel much more secure if given some type of cave within which they can reside. PVC tubes at least partially buried in the gravel are particularly welcomed by those crayfish species that build extensive burrows in the wild. Otherwise ceramic or plastic pipes cut in half lengthwise and placed on top of the substrate can be used for form shelters appreciated by most crayfish. Alternatively you can allow the crayfish to dig its own home by resting a large flat rock (like a slate) on top of several inches of gravel.







Having plenty of hiding places is especially important when attempting to keep more than one crayfish in a container. Some species are are fairly tolerant of one another provided they are not overcrowded, but others are very territorial and aggressive. Even the ones that are not aggressive toward each other most of the time may decide to attack and consume a tank mate who has recently molted. During the molting process the crayfish is weak and the body is soft and vulnerable, making it an easy meal for a hungry tankmate. Providing plenty of hiding places gives the molting crayfish a chance to escape attack during this dangerous time.



Ideally, you should remove a crayfish from its tank mates before the molting process begins and only replace it after the exoskeleton (‘shell’) has completely hardened and it is active and feeding normally. How will you know when a crayfish is getting ready to molt? Crayfish, like most other crustaceans, stop feeding shortly (usually at least a day or more) before shedding the old skeleton. If you notice that a crayfish in your collection is not eating, that could mean that it is about to molt and if maintained in a multi-specimen aquarium now would be a good time to isolate it from its tankmates. Of course loss of appetite can indicate other problems as well, so you should also check water quality and chemistry parameters and look for any signs of disease or physical damage.

Water Quality



If no filtration is used, the water will have to be completely changed on a regular basis, at least once per week. If gravel is used in the tank it should be vacuumed or rinsed to remove excess detritus. Otherwise a bare bottom is fine to use and easy to keep clean. Ornaments and the sides of the tank should be left untouched to leave sufficient beneficial bacteria to keep the water adequately clean. If you detect ammonia or nitrite in the water at any time that means that there aren’t enough bacteria in the tank as it is, and adding a filter will be useful.

Undergravel filters are not the best choice for crayfish since these burrowing animals will move the gravel about creating exposed areas of the filter plate dramatically reduces the efficiency of this type of filter. Internal or external canister filters as well as hang-on-the-back filters that provide for biological filtration are a much better choice. Air-powered sponge filters also work great but I have found that some species like to chew on them. This never seemed to harm the crayfish, but the filter will have to be replaced after they have shaved it down sufficiently. The possibility of their digestive tract becoming impacted from the indigestible sponge material should not be completely ignored, but I have never seen any evidence of this hypothetical problem.



[Editor’s note: like Justin, I’ve also noticed that large crustaceans such as crabs enjoy picking away at sponges. Most likely they consume the organic matter trapped in the sponge and discard the actual sponge material itself. Even if they do eat some of the sponge, I agree with Justin that this doesn’t seem to cause them any harm.]



Temperature



Crayfish come from both temperate and tropical zones, and water temperature will depend upon which species you are keeping. A heater is not required and should not be used in tanks holding most of the North American species, though species from the southern United States can tolerate temperatures as high as 82 degrees F (28 degrees C) without problems. Two very popular North American species are Procambarus alleni and Procambarus clarkii, both of which are species from the southern US. Colorful varieties are grown in large numbers in ponds specifically for the aquarium industry.



But other North American species are showing up in the trade, albeit on a much smaller scale, and in the case of these less frequently seen crayfish you should make sure you know where they come from so that you can maintain them at an appropriate temperature. As a general rule though, erring on the side of keeping North American species too cool is better than keeping them too warm, and most do well left at room temperature.



Australian species are increasingly popular, and most of those require tropical temperatures around 77 degrees F (25 degrees C).



[Editor’s note: In the United Kingdom, it is illegal to keep coldwater crayfish in home aquaria without a specific license. This is because at least one North American species has become widely established in British rivers, and by spreading a crayfish plague has lead to the virtual extinction of the native crayfish. Any crayfish legally sold in a British tropical fish shop will be tropical species from Australia, and consequently must be kept in a heated aquarium.]

Feeding



Crayfish are omnivorous scavengers, feeding primarily on plants, algae and organic detritus. Crayfish do not often find sources of animal protein such as a dead fish, and such meals are very precious to them, aggressively defending such a meal against other scavengers.

But will crayfish actually kill and eat your fish? In an aquarium it is uncommon for crayfish to catch and eat healthy fish, though the odds on such an event depend on the size of aquarium, the number of fish in the aquarium, what species of crayfish is being kept, and even whether the crayfish is well fed or not. So while it is unlikely that a crayfish will catch your fish, there is a possibility, particularly where small or slow moving fish are concerned. Most of the time crayfish are seen eating a fish that fish was already dead or dying, and the crayfish was simply doing its natural duty of being a scavenger. Without knowing this, the aquarist might falsely accuse the crayfish of murder when he notices the crayfish chewing on the carcass!



Crayfish need to be fed a small amount of food every other day or so. Any excess food should be immediately removed. Foods to feed your crayfish include leafy green vegetables such as Romaine lettuce (or other varieties); dried seaweed like Nori; sinking pellet foods such as shrimp or algae pellets; flake food; and freeze dried or frozen foods such as fish, krill, tubifex worms, bloodworms, squid, clam, etc. Since animal protein is rarely encountered in the wild, it is best to feed crayfish mostly plant or algae based foods, and only supplement with animal flesh. However, some aquarists feed strictly shrimp pellets with no apparent problems.



If a crayfish remains soft for an extended period of time, i.e., for more than one day after molting, this can mean that it is not receiving enough calcium in its diet or that the pH or hardness of the water is too low. Transferring the soft specimen to water with high hardness can help if this is the problem, but it is best to avoid this problem by keeping crayfish in hard water and feeding them foods rich in calcium. There are some brands of foods specifically formulated for crustaceans that have a higher level of calcium added, such as JBL NovoCrabs Food Chips and Sera Crabs Natural Complete Diet. Calcium can also be added to other foods by dabbing moist food with a small amount of calcium carbonate powder before feeding your cray.



Crayfish sometimes die during the moulting process, a problem apparently caused by an iodine deficiency. Iodine, in the form of potassium iodide, can be added to the water on a weekly basis to alleviate problems with the molting process. Iodine drops sold for use in marine tanks work well for this, though a half dose rather than full dosage is all that is required. Foods that contain the algae Spirulina sp. or Chlorella sp. are naturally high in iodine and can be helpful as well.





Disease



It is a very bad idea to mix together crayfish from different continents. While there is a risk of spreading disease when crayfish are placed in the same tank as another one, one disease in particular poses a very great threat. Known as the Crayfish Plague it is carried by North American crayfish species. It is a fungus, Aphanomyces astaci, and American crayfish have apparently evolved to tolerate the fungus without much problem. However, it is lethal to many other types of crayfish, including those from Australia and Eurasia.



Never place any crayfish native to another continent together with those from North America. In addition, be very careful not to share any equipment such as nets or buckets when working with North American and non-North American species. The same precautions hold for gravel, pipes and other decorations.



Another disease that can threaten crayfish is White Spot Disease. This is primarily a disease that effects shrimps, but may be transmittable to crayfish if they are fed with raw food made from infected shrimp. Be sure that any food containing shrimp has been cooked in order to destroy the virus.



If you intend to keep multiple crayfish specimens in a single aquarium, be sure to quarantine all new crayfish specimens for at least a month before adding it to the main aquarium. That said, realize that crayfish diseases are often difficult to recognize and even more difficult to treat.

A final and very important comment!



Do not ever release any crayfish maintained in captivity into the wild. Also make sure that there is no possible way for the crayfish to escape into the wild; this is particularly an issue when keeping crayfish in ponds or outdoor fish houses.

Crayfish can disrupt entire ecosystems if they are introduced into areas where they are not native, as has been the case in many parts of the US and UK. Some US States have begun imposing regulations on the transport of crayfish for this reason, and in other parts of the world there may be restrictions on what crayfish can be legally sold as pets. Even if you think that a particular crayfish is native to your area, there is still the risk of introducing diseases into the wild crayfish population.



Many crayfish are only found in specific microhabitats within larger bodies of water. So even if they are native to your general area, you may be placing them in inappropriate waterway in that area. Furthermore, while there are many crayfish species with very wide distributions in a general sense, in terms of genetics and morphology there may be very distinct populations of crayfish within certain areas. It’s likely some of these populations may end up being recognized as distinct races, subspecies or even new species, so let’s make sure the genetics of different populations stay in their natural state so that researchers can get this issue straitened out!



Crayfish can make fascinating pets, but please be responsible and ensure that your crayfish stays contained. Any unwanted crayfish should be humanely euthanized or given to a responsible person who understands this issue and will house or destroy the crayfish as required. Crayfish on WWM:



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