need help

[salty dog]

i was just looking at my tank trying to find what ever has been eating my fish and i noticed something that looked like a blue crab. but i only have had 2 red crabs and they are all still alive this crab was dead and the size of a little smaller than a dime could this be it that ate the tail off my 1 inch gobi? i have had the tank for 2 months and have not seen anything strange or this crab i just found. and now a crab just pops up i am new at all this and i really am lost lol. i have been thinking it was a mantis. i have jbj 28 20pounds of live rock a cleaner shrimp and 3 snails left.

[salty dog]

any ideas??

[Playa-1]

any ideas??
It sounds like you have a Blue Crab alive in your tank. I think the crab would be #1 on the suspect list for snatching tails off of your fish.

[salty dog]

but one that small and when i found him dead he was out of his shell. my gobi was the size of a tube of chapstick

[Playa-1]

They are very strong for their size. One time I had a small crab in my tank about the size of my fingernail. I decided to try and catch it the way we used to catch crabs in the Ocean with a piece of meat on a string. I rigged up a sturdy stick with a piece of string tied to the end. I got a frozen Silverside and wrapped the end of the string around the fish several times so that it wouldn't slip off and tied several knots in it. Keep in mind this lil Siverside bait fish was about 4 or 5 times larger then the crab and It should have barely fit into the hole that the crab was in. I maneuvered the fish in front of the Crabs hideout and that lil sucker came out grabbed that fish and proceeded to pull it into the hole. At one point we were playing tug-o-war and I couldn't get the crab out. The crab pulled the fish so hard that the string went completely thru the fish. The crab got the fish and I got my string back with my loops and knots still tied securely. I was amazed at how strong that lil crab was. After that he would poke his head out and laugh at me from time to time. I finally got fed up with him and had to fresh water dip the rock to get him out of it. They are also very sneaky that crab was in the tank almost a year before I realized there was a crab in the tank. It was only because I caught a glimpse of it one day in the rock work that I knew it was in there. That was my crazy experience with a crab in the tank :lol: It's not uncommon for people to discover much larger crabs in their tanks that they never knew were in there either. My concern is always that there is more that I haven't discovered yet.

[salty dog]

so do you think this is what got my fish and i am safe to put new fish in the tank or? i showed the lfs my half eaten gobi and they said it was probably a mantis shrimp but i have heard no clicking or nothing and the only thing i have seen in my tank i didnt put in there is that crab. and also could that crab move all the sand from under one of my rock

[bertoni]

Crabs can do a lot of damage and move a lot of sand. Your tank might have more crabs or a mantris shrimp, though. Hard to say. I might try making a trap out of a soda bottle and see what it catches.

[salty dog]

the lfs let me hold a trap and i put a piece of shrimp in it do you think that will work or should i do the coke bottle also how long and when should you put the trap in

[bertoni]

I'd put the trap in overnight, every night, for a few weeks, and work from there.

[Playa-1]

It's hard to say why your fish died and what ate it. The fact that you saw what appeared to be the remains of a blue crab in the tank tells me you probably have a blue crab in the tank. What you saw was likely a molt. The Crabs molt as they grow and they periodically shed their hard shell and form a new one. Crabs are highly suspect because they are Opportunistic feeders. If they could sneak up on your fish when it was sleeping then they would likely get a tail sammich. I would use a red lens on a flash light and take a careful look into the tank after all the lights are out for a few hours. You never know what you might see lurking around in the tank. I'm not sure that I would run right out and replace the fish until you have a better idea of what happened to the last one. I agree with Bertoni and the Crab trap is also a good idea.

[salty dog]

ok will do thanks for all the help!

[bertoni]

You're welcome! Good luck!