"Freshwater" Crabs

I think you are referring to the red clawed crab. They are similar in appearance to fiddlers, but fiddler males have one claw that is significantly larger than the other. (Correct me if I'm wrong and you are indeed talking about fiddlers.)

While red claws can be kept for a time in freshwater and in the wild habitat both fresh and brackish water, it's not feasible for them to be kept in freshwater longterm whilst in captivity. Eventually they will need a brackish water set up.

You don't need a special filter, but you will need a hydrometer to measure your salinty as I'm sure you're already aware of. I can't give you any more information than that in regards to the brackish requirement as I've never kept brackish myself although I do know they the salinty should be 5-15 ppt. As far as all of the other water parameters its pretty much the same as a majority of freshwater species (very low to 0 ammonia, 0 nitrites and nitrates) although I have heard they prefer a somewhat high ph. They also need a temp of 70-85 F.

These guys are really easy to feed however and will eat just about anything: shrimp pellets, algae wafers, blood and tubefix worms and even plants and veggies. I've also seen them eat small fish that venture too close, however I have heard of instances where people kept them with fish successfully.

Males have larger, redder claws then females and their bodies are also a bit larger. When put side my side I find it's fairly easy to tell. The problem with red claws is that they have a tendency to fight amongst each other especially males. They are also a fairly messy little things that's why I really would only recommend one maybe two max in your five gallon.

It may not seem like much, but trust me on this. And don't ever use pet store stocking methods as a guide. They always overstock.

LOL.. I work at PetsMart! And we sell red clawed crabs at mine. However, it may be different at the one you went to.

EDIT: After a bit of brain racking, the only other crab I think you could have seen would have been a "mini crab" which is a type of fiddler. This is the only other type of "freshwater" crab I know of that PetsMart carries. The females tend to have white looking claws like you described while the males tend to look more gold and have the trademark large claw.

Yes, their care is virtually identical. However, I do think they prefer to have a salinty that's a bit higher. I'm going to try and find out in the next few days exactly what species of fiddler crab PetSmart carries as I'm sure you'd like to know should you choose to keep them. I'm rather curious myself.

If you're talking about either red clawed crabs or fiddler crabs, both need access to a land area and need significant levels of salt in their water. They actually do best in a brackish water setup, but if you have freshwater with quite a bit of salt in it, they'll be alright.
beefsteak gave you some great information. You can post in the brackish water forum for more info on how to mix brackish water and filter it properly.
A good reference page is:
http://en.wikipedia.org/wiki/Fiddler_crab
as well as
http://www.fiddlercrab.info/

My fiddlers were the worst in trying to escape. I used a screen over the top of the tank, which cut down on filter rescues, etc. You'd be amazed what they can fit into. Any crack, any gaps, they're gone.

Hi, I've got two Rainbow Land crabs, http://www.freewebs.com/rainbowcrabpart2/crab3.jpg
you can see from the link they have white claws, coloured shell. Mine live in a 2'x1'x1' tank, gravel bottom, and a large water bowl sunk into the gravel. They are fruit eaters, apple, pear not citrus fruits,plenty of foliage, I use small ceramic pots as hiding places. Interesting creatures, very shy.
Liz

are they aggrassive and how big do they get?

do the red claw crabs have to have access to land?
The guy at my petsmart didn't say they did