kevinoh33 wrote:I had been keeping fiddlers for a while and I had one crab who lost his big claw for some random reason :roll: . Once they lose their big claw, the small claw starts to grow into a big one! It was really fascinating

Actually, I had a different experience (although I assume it is the same brown fiddler crabs caught from the amazon imported here you are talking about). I had a fiddler lose a big claw (presumably from a fight with a rival male in the same tank) and I presumed the remaining small feeder claw would grow into the big one in the next molt.
Well, my crab molted (

) but instead of the feeder/small claw growing into the big one, it actually just replaced the missing big claw with a half-sized, erm, big claw on the next molt, I kid you not.

So it had kept the tiny feeder claw, and the big mating claw was only half the size of its tankmates
Sadly, I don't recall it molting the next time after that - it probably was nearing it's expected life span end, I think (well, I would like to think).
Edit: Oh, by the way, with the big-claw-less fiddler mentioned by the original threadstarter, I wouldn't worry too much yet. I would just continue feeding normally. However, if this wasn't a result of a crab vs. crab fight, I would take the precaution of adding marine iodine to the water perhaps to aid in molting. Marine iodine supplements can be purchased from the marine aquarium sections of the petshop. In addition to this, I would break off a piece of cuttlebone and add it to the water to harden the water a bit. Hope this helps. 