Are emerald crabs known to be aggressive?

[ReeferWarrant]

Yeah, I was looking at doing a FW tank with a panther crab or some sort of crawfish. Until I learned they like to rearrange everything and destroy your placement of anything. If you have a sump I would put it in there. You might have to feed it though, but if that LFS is worth anything they'll take the return. If not, I wouldnt go there again.

 

[msavoy]

Crabs often will eat fish. I don't allow anything in my tank which doesn't have fins.

Yep, I completely agree with you. I just woke up this morning and now my cleaner shrimp has also been torn apart. As soon as I find this dang emerald crab it’s out of the tank

 

[Salted]

Ok maybe that’s the issue I’m having then. I have a new tank so not a lot of algae yet. A lot of diatoms but I’m not sure if they like those. I got a tiny one thinking he’d find somethings to eat but maybe he’s not getting enough.

Focus feed him. Mine gets sooo excited to be given a bit of shrimp or fish on a stick. Really entertaining for me.

 

[walloutlet]

Focus feed him. Mine gets sooo excited to be given a bit of shrimp or fish on a stick. Really entertaining for me.

I do this as well. Mine will literally crawl on the tube to try and get the food. So far I've only witnessed my Emerald picking at some algae in-between my Zoa polyps on the frag plug. Hasn't been picking at them directly. I just make sure everyone is well feed and content with the hope that it reduces any aggression and competition. However, all the critters in my tank definitely have a mind and personality of their own!

 

[Clownfish_Boy]

Crabs love shrimp and other crustaceans and snails; and sometimes fish. I once put a Sally Lightfoot crab in a previous FOWLR setup, soon after introducing the SL crab my snails and hermit crabs began to disappear until they were all eaten. I had also added a couple of Emerald crabs, but they soon also disappeared, never to be seen again. I'm thinking that the only really compatible crabs must be small Hermits.

 

[CavalierReef]

My emerald has been in my tank as part of the initial clean-up crew for six months. He shares the tank with a Wheeler's Goby/Tiger shrimp combo, two scarlet shrimp, a firefish and a McCosker's Wrasse. So far he has bee a model citizen. I've seen him harvesting algae off a plug but never seen him bother a polyp in my LPS dominate tank. He is very active cleaner and a welcome member of my little crew. Of course, your mileage may vary.

 

[homer1475]

FWIW emerald crabs lack the sharp pointy claws to kill fish. @Clownfish_Boy is dead wrong about emeralds. They will on occasion kill a hermit or snail for food, but they move to slow, and their claws are blunt, they lack the ability to kill fast moving fish.

They are like any crab though, opportunistic eaters though, if they find a dead body, they will most certainly chow down on it.

If you have a crab killing fish, it is not an emerald.

 

[Clownfish_Boy]

FWIW emerald crabs lack the sharp pointy claws to kill fish. @Clownfish_Boy is dead wrong about emeralds. They will on occasion kill a hermit or snail for food, but they move to slow, and their claws are blunt, they lack the ability to kill fast moving fish.

They are like any crab though, opportunistic eaters though, if they find a dead body, they will most certainly chow down on it.

If you have a crab killing fish, it is not an emerald.

Guess I may have been comparing apples to oranges in my experience with a Sally Lightfoot, @homer1475 . They must be far worse than an Emerald.

 

[Peacocksm]

I have 6 emerald crabs in my tank. They mainly eat the red algae. I do have a larger one who will grab a frag and try to drag it under a rock. But for the most part they stick to their rock and clean/eat

 

[samnaz]

They’re aggressive alright, but their pincers are small/flat and the only damage they’re capable of is to immobile or defenseless creatures (algae, coral, etc). I’m willing to bet this emerald didn’t kill your shrimp. Mine can hardly manage to pry bubble algae of rocks and eat it. He does, but he struggles and it takes time.

The secret to emerald crabs is to feed them meaty pellets if they have lost taste for algae or are being destructive. They are opportunistic feeders. Mine eats whatever he feels like, even attacks my tongs if they come close, or my hand waving outside the tank far from him. He’s super feisty.

 

[ariellemermaid]

I’ve heard male emeralds are more aggressive than females. This has definitely been our experience. We used to have a male who picked on corals. Now we have a female and she eats only algae and seaweed strips. She rarely strays from her hole in the rock / cave. I agree with others who stated you might not actually have an emerald; they should be green in color. If you want an emerald, I suggest picking one out in-person at a pet store rather than ordering online. That way you can be sure to select a female. They are pretty easily distinguished:

Emerald Crab – Detailed Guide: Care, Diet, and Breeding - Shrimp and Snail Breeder

Besides being easy to care for, the Emerald crab is one of the crab species known by controlling nuisance algae, particularly Bubble algae (Valonia spp).

aquariumbreeder.com

 

[droblack]

Crabs get a bad rap because they are indeed, as another posted, opportunistic feeders. Shrimp too. Many start off much nicer, and never quite get as bad as there more aggressive counterparts. But, they can and do learn to eat from more sources over time.

Observed peppermint and cleaner shrimp eating fish food, then stealing fish food from corals, and then eventually eating the corals. This happened over the course of months or years.

Sally lightfoots, emeralds, and even hermits can flip.

"Accidentally" introduced a baby stone crab into my reef system back in the day. Oh, the horror. Now, that is an evil crab. Nearly indestructible too. Had to take about 1/2 of my rock and coral out to get em. Had created a graveyard of coral skeletons within its main home-rock. Still wake up at night shivering thinking of that beady-red-eyed lil demon.

 

[stanlalee]

Emerald crabs are fine when they are small. They are usually sold small but they don't stay small. They are relatively slow and methodical and probably can't catch a healthy and awake fish but they will if they get a chance and the fish is small enough.
Sally lightfoots on the other hand are lightning fast and very risky for any fish or crustacean not big or aggressive enough to deal with them. They are usually sold as reef safe and I made that mistake early into reefing.

 

[gregoryalln854]

You guys got me worried. I ordered 4 emeralds from a vendor on here and one is massive, is it an emerald?

 

[FreeEnergyReefer]

Yep, I completely agree with you. I just woke up this morning and now my cleaner shrimp has also been torn apart. As soon as I find this dang emerald crab it’s out of the tank

Holy ****! He is possessed! Id be ticked! If mine kills my pistol or fire shrimp he's getting thrown off the wall so hard.

 

[gentlefish]

Bottle with some food in there may work to attract him. Place in sand close to him. Easier to remove once in the bottle.

 

[blaxsun]

I had a SLF, and we suspected him of a few fish deaths. Turns out the fish just died and presented him with an easy meal. As has been pointed out, crabs are opportunists and won't pass up a free meal.