I caught three of those exact crabs. Take him out while you still can! They grow bigger and backer and theyre eyes turn red and they destroy your fish! Dont kill him though, he makes a neat pet, he was really good while it was little, its just that as it crew, i guess its apetite did to. Whats strange is it was identified as a shore crab of some kind
Glad to see i'm not the only one being haunted by one of these!!mine is larger then a quarter and is quit a skilled hunter (has eaten 75 plus doller's of food i mean fish). i tryed 4 times to get him but still no luck! i dont want to kill it just put him i a 10 gal to see how big it will get.good luck with your's, just put them in the sump.