I have always been a fan of emerald crabs and have kept them for the past three years. Two of the ones I have now are the green variety and have grown fairly large. The body (not counting claws) is bigger than a quarter, close to a 50 cent piece. Yesterday while feeding my tank. I witnessed one of my green emeralds catch my diamondback goby. The goby got too close and the crab grabbed the goby's mouth. The goby went nuts trying to get loose, but the crab held onto the mouth tight. I had to go in and try to grab the crab so it would consider me a threat and let go of the goby to defend himself. The goby went into his hole for an hour. Later he was out and sifting sand. Hopefully no long-term damage. I think I need to get the two big green emerald crabs out of my DT. The white emeralds have stayed small and never threaten or try to grab fish.