Red crabs in tropical tank ?

Question

My friend has recently set up a tropical tank, cycled etc and finally bought some fish. He has bought some neon tetras and guppies but also 2 red crabs. I have no experience with crabs but these do not look happy - they are sitting still at the bottom of the tank (4 days) and occasionally fall on their backs. You can see the under section of the shell moving up and down.
Is this because they need aquarium salt in the water ?
Will aquarium salt be bad for the fish ?
Please help !!

Answer 1

The red Crabs commonly sold in Aquarium shops are actually a tropical crab called a Rainbow strider. They come from the Christmas Islands, and can grow to be 8inches diameter. They are a carnivore, and although they live in and around pools in general. They are actually a land crab.

They need a tank set up which is mostly moist but dry land, and just a small pool of water.

They do not want salt in the water as this does nothing but stimulate the females into thinking its time to migrate to the sea where they lay there eggs in the surf before migrating back to the rain forests where they live. While under water, the female instinctively thrust their under bellies out, because they carry their fertile eggs there during migration and once completely submerged, they start to thrust to release the eggs into the current.

The reason they stay still under water is because they are land breathers. They have thankfully as an old design to sea crabs, gills which can take dissolved oxygen from the water, but not indefinately, and do need to be able to get out of the water completely, even if its onto a pice of cork bark, or a rock, but bare in mind they can't swim either, so any access to dry land needs to have a rough and gently slope right down to the bottom of the tank.

Your small fish are also living on borrowed time as the rainbow crabs feed on insects and rotting carrion in the rain forests. When the lights go out at night, the fish will settle on the bottom or swim and hide in amongst the plants and decor. The crabs can easily catch the fish or take a big chunk out of them with their claws.

As they eat the fish, they throw clouds of tiny particles into the water around them, and a high percentage of fish oil goes with it, clouding and polluting the tank.

My advice is take them back to the shop, as they are not going to settle in an aquarium set up for fish.

Answer 2

Are your crabs red claw crabs? I'll agree with most of Feral's answer except about the salt. These do need to get out on land - in fact, more land than water would be their preference. And they should have a small amount of marine salt in their water. Not enough that it becomes a saltwater environment, but enough that the pH increases and they have trace amounts of calcium and magnesium so their exoskeleton develops and hardens properly.

Perhaps you'd like to pass the two links below on to your friend so he can see how these should be kept.

The guppies won't mind the salt at all - they can live in salinity higher than seawater if they're changed over gradually (I have a trio of breeding saltwater guppies). The neons, on the other hand, won't like the salt or the higher pH - they come from areas with slightly acidic, soft (not a lot of dissolved minerals) water, which is exactly the opposite of what the crabs and guppies would prefer.

Answer 3

Yes, they are basically the same. More commonly called rainbow crabs. They'll need land access so make sure you provide them with it. They are more brackish water but they can live in freshwater. I do not suggest putting them with fish. Big mistake in smaller aqauriums. 1) No, breeding is not too easy and you need to really coax the female into breeding by adding extra salt to their water. 2) An airstone oxygenates the water and creates water flow which is operated with a pump. A filter is a entirely diffrent thing. 3) You'll want a light for them so they have a grasp on daytime and nightime. Without a light it'll throw them off just like fish. 4) No do not give them common human foods. Bacon and beef heart clogs up their heart and intestines. You can buy crab pellets or rubber band a rock to peas, raw bean, spinach, and raw fish. 5) They are tropical they need 76-80 degrees if your room is that hot then no but I highly suggest a heater. You need a 15 gallon aqaurium with half land (sand) and half water. You'll need an in tank filter and hood as they can easily crawl out of an unhooded aqauarium. Make sure it's tightly fit as possible as they are escape artists. Also make sure they have sand to burrow in and rocks to hide under along with driftwood and plants. A slim heater is advised as it'll get too cold for them in the winter. They like live plants but watch if they eat it. If you have a large enough tank you can put mudskippers in there which I really like. I once had a tropical crabs that were housed with my baby hermit crabs and mudskippers but over time the crabs died of old age (They were 5 and 4 years old at my guess) and they don't sell them here in Japan. Once I go back to Texas I'm sure to pick some up. Feel free to IM me if you have a problem or sickness.

Answer 4

Well if they are sitting on the bottom motionless and the current of the tank is pushing them on their backs them they are probably dead. And if the underside of their shell is the part on the bottom that covers the genitalia area is not being held down, then sounds like it is dead and starting to decay. If they are still alive and they are red clawed crabs, these are actually brackish water crabs and would need a little salt in the water at least, too much salt would be bad for your fish though. Hope this helps.

Answer 5

Red Crabs Aquarium

Answer 6

they probably need a place to get out of the water on. red claw crabs arent meant to always be under water. you dont need salt