FAQ

[Ulli Bauer]

Posted by Beastiependent (Ollie)
Translated by Ulli Bauer

In this thread we're answering the most frequently asked questions posed by crab keepers. It will be amended by and by. The links lead to the German original questions and answers.

• My crab is "foamy", what could that be?
• What's poisonous for crabs?
• My crab has lost a leg or a claw, will it regrow?
• My crab has lost both its claws. Can it eat anyway?[b]
• [b]How can I see if a molt goes wrong? Can I do anything?
• My crab doesn't eat, what's up?
• My crab only eats certain foods?
• How long can my crab stay in the water?
• How long can my crab stay on land?
• I want to/have to add a new crab to an existing group, how do I do that?
• My crab has "rust holes". What is that? See Diseases!

Soon to come:
• The wood in the tank looks moldy - what do I do?
• Do I have to cycle a crab tank?
• Do crabs get tame?

My crab is "foamy", what could that be?
For once, this can be caused by the crab's normal bubbling; during this process water - maybe mixed with some air bubbles - runs across the crab's face, coming from the mouth area, back into the gills. This circulation enriches the water with oxygen again. Some crabs also bubble under water, especially when they have just gone under the surface.

If the crab is really foamy this might be a sign for poisoning. In order to get out as much of the noxious substances as possible it is recommendable to change a lot water very often. Moreover, the crab should be placed in "hip-high" water so that it can breathe water as well as air, depending on which is easier for it.

What is poisonous for crabs?
Crustaceans have another blood blood pigment that most vertebrates (hemocyanine instead of hemoglobine), which makes them highly susceptible to copper, even though they require copper as a trace element in very small concentrations. The copper tests in the aquarium trade are not sensitive enough to detect noxious copper concentrations, however. Lethal doses are as low as a few micrograms (a millionth of a gram) per liter - the lowest concentration that can be shown by most drip tests is at 50 to 150 micrograms. When the water is more acidic, copper is even more toxic than when the water has an alkaline pH.

Lead and other heavy metals are highly toxic, too.

Acids are also not good for crustaceans. Among these are prussic acid (contained in beans, maniok, raw bamboo shots, green elder berries as well as various fruit pits {Kirsche, Aprikose}), oxalic acid (parsley, sorrel and oca; raw chard and spinach - only feed when boiled over!) and fruit acids (citrus fruit et. al.).

My crab has lost a leg or a claw, will it regrow?
Yes, most articulate animals - among them the decapods (ten-legged crayfish) - can regrow lost limbs when they next molt. The new claw or leg will probably be smaller in the beginning and reach its original size after a few more molts.

It is also possible that the crab has released a trapped leg (autotomy or self-amputation) or a claw with which it had pinched a "predator" (which could also be the keeper, of course) so that the firmly grasping claw distracts the enemy and the crab can flee.

If crabs lose a certain amount of limbs they can speed up the molting process (ecdysis) in order to replace some or all of these limbs sooner. Gecarcinus lateralis e.g., the harlequin crab, does this when more than five limbs are lost.

My crab has lost both its claws. Can it eat anyway?
No, when a crab has lost both claws it cannot eat on its own any more, in contrast to crayfish. They have to be hand-fed then.

How can I see if a molt goes wrong? Can I do anything?
It is not always easy to see if a molt goes smoothly or if there are problems. When limbs, mandibles or gills get stuck in the old skin the crab cannot get out and will suffocate or die of other reasons. Molting is a returning great risk in the life of crustaceans and poses one of the main reasons for death.

A smooth molt is most likely when all keeping parameters are good, i.e. temperature, humidity, well-balanced food, good water quality, no territorial stress and many other factors. Despite of this, any molt can be problematic without the keeper having done anything wrong - this process is a risk for crustaceans.

In general, the molt per se should be complete after half an hour to an hour, i.e. the crab ought to have left its old skin after this time. If the process lasts significantly longer or if the animal is obviously stuck you can try to help it along. A leg or a claw can be severed if the crab does not do this itself, limbs will regrow. If the crab's gills or mandibles are stuck, however, help is not possible in most cases.

On the other hand, a crab that got stuck in its skin will die in any case, so you could try to help it anyway, carefully yet with force or nail scissors/a scalpel - basic knowledge regarding brachyuran anatomy is of course requried, or else that operation wouldn't make sense. On the other hand, things can hardly be made worse anyway. If you feel you're capable of helping it... However, every keeper has to decide for him or herself when to intervene, this is not easy in any respect.

My crab doesn't eat, what's up?
Maybe it is getting ready for molting, even though there might be other reasons. However, crabs do not necessarily have to eat a certain amount per day. Many crabs - especially from mangrove and shore areas - eat fallen tree leaves as a main food (which ought to be in every tank they are kept in, too), but they can get by without food for several days to a week. Starving to death will take a crab at least a few weeks.

A crab not eating for one or a few days is not really a reason to worry.

My crab only eats certain foods?
Make sure you don't train it to specialize on food! Give only one kind of food per day, not a menu with various foods.

Crabs are the highest-developed crustaceans and thus real individualists - in some respects like us humans. They have preferrences, generally and specially. I.e. there are crabs of one species that like certain foods more than others, and other crabs of the same species do not eat that food, but also that they eat food "X" for a certain time, but ignore it totally only maybe three days later and rather have food "Y" instead. This is the same with humans, and here we simply call that "appetite"!

Most crabs are omnivores (eat everything), some are more on the carnivorous side (eat meat) - e.g. Cardisoma armatum as scavengers, Geosesarma sp. "vampire" –, others are rather herbivorous (eat plants), like e.g. red mangrove crabs (Pseudosesarma sp.). However, many rather herbivorous crabs like animal proteins anyway (insects, shrimp et.al.), however, the animal food part should be a lot lower than the percentage of vegetable food, e.g. only once a week.

A general pointer as to crab food can be found here: http://www.panzerwelten.de/forum/showthr...p?tid=1453

How long can my crab stay in the water?
Freshwater crabs can stay in the water forever, they don't need a land part and don't have to go to the surface regularly. Most mangrove or tidal crab species can also stay under water all the time in principle, however, they like staying at or above the waterline from time to time, so maybe this is even necessary for them.

With land crabs things are a little more complicated, for more information please see:

The next post: How long can my crab stay on land?

How long can my crab stay on land?
Land crabs can stay on land perpetually, given that the air is humid enough or that there is water in their burrow (which they need primarily for their gills), no land crab will enter the water. Gecarcinus lateralis, G. ruricola and G. quadratus (Halloween crabs) for instance shy away from water in captivity and only go to the sea in nature in order to release their larvae - and some even drown doing this!

Cardisoma armatum (rainbow crab), in contrast, can take up as much oxygen under water as on land. Given that the humidity is high enough, this species only needs a water bowl. If they have access to a water part, however, they make extensive use of it in our experience. Even staying under water for weeks does not harm them.

However, if the surroundings are really dry, real land crabs of the genera Cardisoma, Gecarcinus or Gecarcoidea will survive for a maximum of three to four days without hydration.

Many species are amphibic (or semi-terrestrial) and can live under or above the waterline (given that the air or the substrate is humid enough) for longer periods of time. Among these are, for example (!), "red mangrove crabs" (Pseudosesarma), some Geosesarma species (some of these can drown, others are extremely terrestrial) and all Sesarmidae (mangrove crabs) as well as Grapsoidea (tidal crabs), but some freshwater crabs as well.

I want to/have to add a new crab to an existing group, how do I do that?
If you want or have to add a new crab to an existing group you best take out all the animals, re-decorate the tank or terrarium (e.g. move the wood for some centimeters, put a stone in another place and so on) and then put all the crabs back in, the new one preferrably first.

Thus all the crabs have to find new hideouts and stake new territories (the latter mostly applying to the males), and the new crab is not as disadvantaged this way.

If the tank is clearly understocked though and if there are lots of free hideouts and enough room you can just add the new crab - however, when in doubt it's always best to use the more complicated method.