Crabs can regrow their claws

Typical diseases in crabs

Health problems and their diagnosis

External parasites and injuries are a comparatively minor problem for crustaceans, because the decipedes are able to renew their old shell and thus also lost or injured limbs.

Poisoning and / or other metabolic diseases can be insidious and are therefore often only noticeable when it is already too late. The animals can bring stresses of this kind with them as they are frequently caught in the wild (many species of crabs), so research into the cause or even diagnosis and treatment is almost pointless.

A reliable diagnosis is difficult at all, because the shell itself is often not vulnerable, and it is not always easy to make a clear diagnosis based on the joints.

If a fungal disease is detected, many drugs for fish and other terrarium animals cannot be used because they contain substances that invertebrates cannot tolerate. (Many other pests are also invertebrates, so they cannot be used.)

Sometimes an improvement in living conditions and the gift of natural aids help. Sea almond leaves and alder cones have a mild fungicidal and antibacterial effect - also preventive.

Incorrect, one-sided and too well-intentioned nutrition for crustaceans in general can also lead to metabolic diseases and affect the molting process. For crustaceans, less is more.

Stress and anxiety

All crustaceans are extremely susceptible to stress of all kinds. Lack of space due to excessive stocking - be it by conspecifics or other animals - lead to susceptibility to disease and, in crabs and crabs, to fights that can lead to death. Occasionally, behavioral problems can also appear (killer crabs).

If the situation improves, these symptoms can also go away again. A leg that is lost every now and then is not a cause for concern.

Shrimp and crayfish often lose their color under constant stress and become more and more anxious. However, it must be borne in mind that this is also the case shortly before a molt.


Despite the great adaptability of crustaceans, there are some sources of danger that need to be considered. Tap water - at least the hot pipes - can be contaminated with copper; this needs to be clarified when crustaceans or other invertebrates such as snails are to move in. The cold water pipes, on the other hand, can almost always be used.

Another cause of poisoning - especially in the case of the small shrimp - is insecticides. Aquarium plants are treated more or less with them during cultivation. If you want to be on the safe side, you should water them for a few days before using them in an aquarium or aqua-terrarium with crustaceans.

Fruit and vegetables must be peeled or washed unless they are organic. If the causes of poisoning, which are usually expressed in the form of cramps, are to be found in the immediate vicinity, such as excessively polluted water (nitrite), transfer to fresh water can be the solution.

The moult

All crustaceans molt in order to grow. Getting out of the old dress is only the part that is visible to us. Preparation and follow-up care can take several weeks, so that after the molt is usually before the molt. This process plays a central role in every crustacean life. Only a short period of time is not subject to this risky feat of strength. The eating and living habits are strictly subject to the respective life or moulting cycle. There are times when the appetite is huge, and shortly before the event, the animals will stop eating.

In addition to the formation of lost limbs, many internal parts of the body also undergo a complete renewal: the stomach, the gills, even the hair on the legs.

In addition, a new chitin skin forms under the current dress, which only fills with water after getting out and thus becomes larger. Then the new dress hardens slowly by means of food reserves inside the body, and new tissue is formed.

During this time, crustaceans are very vulnerable due to their soft skin and therefore like to withdraw (butter crabs).

The exit

Crabs and prawns tend to get out to the side. Krabben tears the seam between the last pair of legs. However, this has a different effect, because crabs have folded their rump (pleon) under their belly over time, which crabs and shrimps carry elongated. This gives the crabs their compact shape and also means that the stripped skin often looks confusingly similar to a real animal. When seeing the so-called Exuvie for the first time, many shrimp keepers think that their darling has died. The amazement is great when suddenly supposedly two individuals are sighted.

Water is an important element in a molt. It ensures the enlargement of the still soft skin, and the calcium for the first stability is removed from it. Crustaceans that molt in the water can use the buoyancy for relief. Rural, i.e. terrestrial, crabs often have a widened head chest area (carapace). Here, and also inside the body, they can store water, also naturally in connection with a molt.

Cancer plague and burn mark disease

The particular severity of cancer plague lies in the fact that native cancers fall victim to it, while American crabs, for example, are only carriers of the pathogen, a filamentous fungus. They therefore do not belong in the garden pond or exposed under any circumstances! The epidemic can be recognized by brittle, damaged armor, apathy, convulsions and paralysis; In the final stage, thread-like structures often appear on the joints. The whole thing ends fatally within a short time and can destroy entire stocks. If the disease breaks out, everything that has come into contact with the aquarium and the aquarium itself must be subjected to intensive disinfection.

The burn mark disease is shown by black-rimmed holes in the chitin armor, also caused by a fungus. However, there are also sporadic spots that do not necessarily have to be severe or even fatal.

Ultimately, many illnesses, including the less fatal ones, can often be traced back to inadequate living conditions. This weakens the crustaceans, and so they offer a welcome target for all sorts of harmful organisms.

frequently asked Questions

  • My crustacean is missing a pair of scissors - can it survive? Basically yes. During the next molt, which many crustaceans may prefer, a smaller, new specimen grows first. If you have the impression that the one-armed animal is weak, you can chop up food and offer it in this form, provided that it is crabs. If both scissors are missing, the cause must be found and, if necessary, eliminated (lack of space). If the respective animals are fed, they may have a chance. Crabs also have other small claws that make it easier for them to eat when the big ones are missing.
  • My cancer is on its side and stuck while shedding its skin - should I help? Better not, because you never know what's stuck in there. In addition, they must not be touched. Even if it's difficult: wait and see that the same doesn't happen to the others.
  • My crustacean is deformed - why? Malformations in the limbs are mostly due to incorrect or one-sided nutrition and are often a sign of food that is too rich in protein. If this is adjusted, there may be a chance of improvement during the next molt.
  • My crab has a dark mass under its belly that is getting bigger and bigger. A female with spawning grains in the brood chamber. Crabs and shrimp carry their offspring in the same place: under their abdomen. The eggs are attached to what are known as pleopods. Many species of crabs release unfinished larvae into the salt water after a few weeks, or even small crabs, shrimps and - depending on the species - even crabs hatch.
  • My crab suddenly loses all limbs - what's wrong with it? This mysterious phenomenon can be traced back to an infection and is fatal. (Annette Berkelmann)

Photo: © wake99 (CC0 Public Domain)