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Mystery Crab Caught!


albertareef
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So... after several disappearing fish and occasional "claw" sightings, I may have found and caught a potential culprit! I couldn't get pics of mine (dead camera battery) but it looks just like these photos of a black mithrax. Hard to tell scale here but mine was about 2.5 inches across. I had tried the baited mason jar approach before with some scallop meat - no luck - but then tried it again with some nori tied to a rock. Bingo! Success first time! Anyway, not sure if this is the fish killer or not but I am glad to have it out of the tank! Thanks to those that suggested this trapping technique - I owe you one!

 

Sean

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When I first saw that 2nd thumbnail pic, I thought "aha!...a fish-eating swimming crab!"

Then looking closer, I noticed it does not have the "paddles" on the last set of legs.

 

Although it looks very much like and aggressive swimming crab in body shape, it is not. Still, it has a good set of claws, so keep an eye on it!

 

Has anyone ever caught Blue Crab like they have in Florida?

Then you know how aggressive the are when they jump out of the bucket trying to attack you!(laugh)

 

If what you have is a species of Mithrax Crab, they are known for sometimes becoming "semi-aggressive" but rarely harm fish.

 

As suggested in this article, http://www.wetwebmedia.com/swcrabcomp.htm a baited tray might be used in removal of the crab. You might tie the "bait" up in some bridal veil fabric attached to the tray to keep it around until you can haul it up!

Making a mini crab trap sound like a fun project. Happy crabbing!;)

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Yeah - if he is the culprit' date=' he has had a very expensive diet up to this point! I'm trying hard not to add it up...[/quote']

 

YEa, I had a brittle star like that. He had high dining needs to say the least. $40 worth os sea hares, plus another $20 to $30 in snails and crabs. I think he is who got my corus wrasse also(flame). You've probably heard me say it before but he is "Doin' time" in Seahorse Aquariums Refugium penitentiary. He is now committed to a life of no meat until further notice...:p

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It should be noted that a crabs claws can serve many functions.

 

Among these functions (and definately not limited to):

 

1.) Catching prey items

2.) Ornamentation for attracting a mate

3.) Defence

4.) Offence

5.) Intimidation

 

Seeing a large claw does not mean that the crab is a fish killer. These large claws could be to attract a mate, or any of the above listed functions, or other functions.

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I have a very similar crab in my tank. He has been in there for a couple years. I would love to catch him but have had no luck. A couple close calls but nothing yet. He has never seemed to cause any damage. No fish missing, no coral damage, etc. The very few times I have seen him he just eats algea and other debri. (nutty)

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I have a very similar crab in my tank. He has been in there for a couple years. I would love to catch him but have had no luck. A couple close calls but nothing yet. He has never seemed to cause any damage. No fish missing' date=' no coral damage, etc. The very few times I have seen him he just eats algea and other debri. (nutty)[/quote']

 

Yeah - as Doran points out, there is a good chance that he is actually harmless but, given my history of disappearing fish, I just didn't want to take the chance so he is now living in my sump.

 

Someone suggested the trick I used to catch him which was to tie some nori to a piece of rock and put it in the bottom of a tall glass (or mason jar in my case) then prop it up against the rockwork in a spot where he could climb in and leave it overnight. The slick, straight walls keep him from climbing back out. I tried it once with a scallop and had no luck but the nori trap got him first try!

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