Emerald crab problem

I have/had a couple emerald crabs in my tank as of last weekend.. I went saturday and purchased a mandarin thats was beautiful.. When we got home from going to eat Sunday I found one of the crabs holding the mandarin and half of the fish had been ate! Needless to say the fight was on.. 2 hours later I caught the crab and maybe hes doing the septic tank some good cleaning now (it actually maybe alive with all the water changes I have been doing as its probably full of salt water :)

Anyway, I have a couple more crabs and not sure how hard to try to catch them.. Is this normal behavior of crabs to catch and eat fish???

 

i think it more likely that the crab scavenged a dead or dying fish.

 

I've read tons of horror stories like this regarding crabs of all sorts... Seems like they're kind of hit-and-miss as to whether or not they'll be a problem. That's why I got rid of my only emerald crab after my bubble agae was eaten (hasn't come back yet, thankfully).

Anyway, I caught my crab by taking a plastic bottle and cutting the bottom off at about 4 inches (the depth of my sand bed). I stuck it in the substrate so it made a little hole with a shear 4-inch drop, stuck some seaweed in the bottom (maybe try something meaty for yours?) and let it sit overnight...next morning, he was trapped in the bottom (along with about 6 hermits) and couldnt climb out.

 

I had wondered about the fish being the issue but it had only been in the tank for a few hours and seemed to be doing great when we left. Was only gone for couple hours so I guess it could have deteriorated.. Anyhow, I got the emerald for bubble algae as well and now I dont see any so the need of the crab is not there. Although, they are fun to watch with the exception of watching them eat your beautiful fish!

 

While I really don't trust most crabs I have had Emeralds in every tank I have ever owned and they have never eaten a fish. It is very difficult to tell whether a fish has been killed by a crab because they do eat dead or dieing fish. Unless you have actually witnessed it killing a healthy fish I seriously doubt that was the case although it is possible.

 

two hours does seem kind of fast. crabs are opportunists. the fish could have been in shock and a little sluggish and picked the wrong place to lay low. I just have a hard time picturing my emerald crabs actually being able to hold on to and kill a healthy fish. how large was this crab?

i just keep picturing an episode in my tank a couple of years ago when i bought a mandarin that i wasn't ready for. The mandarin slowly deteriated and was in its last week when one of my larger hermits decided to grab its tail. i just happened to be watching as this sick fish shot across the tank dragging the hermit half of the way with it until the hermit fell off. granted, this crab was probably smaller than your culprit but this fish was almost dead and still had enough fight to throw the crab off.