Poll: are emerald crabs fish safe?

Discussion in 'Reef Aquarium Discussion' started by demeyer2, Feb 7, 2018.

?
  1. Yes. I've had them before with no problems.

    453 vote(s)
    68.5%
  2. No. I've had them before and can safely say they have killed healthy fish.

    36 vote(s)
    5.4%
  3. Never had one - too scared of the horror stories.

    76 vote(s)
    11.5%
  4. None of the above.

    96 vote(s)
    14.5%
  1. demeyer2

    demeyer2 Active Member Build Thread Contributor

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    My tank is fairly small (Red Sea Reefer Nano). 21 gallon display with 6 gallon sump. I have some algae in the DT that is a bit too big for the standard CUC crab. The algae problem isn't that bad as my entire sump is a big refugium powered by a Kessil H380, but still there are some patches and they're growing slowly so I want to get ahead of it. I don't want to feed less (I feed the fish once per day and the corals twice per week) as my SPS coloring loves having some nitrates in the water.
    I've been thinking about getting an emerald crab to go after this algae, but my research on how safe they are has been very inconclusive, which is why I want to do the poll. I have two clowns, 1 helfrichi firefish, and 1 Biota captive-bred Mandarin from AlgaeBarn (don't worry he eats prepared foods and is the fattest fish in the tank :D). Having said that, these are all small fish. I'm not too worried about the clowns, but the firefish and mandarin sleep in the rock work and I don't want them to fall victim to the emerald. Thoughts?
     
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  2. Vaughn17

    Vaughn17 Well-Known Member

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    I have about a dozen emerald crabs (some quite large) in a 180 that has two mandarins, a pipefish, a Hawaiian cleaner wrasse, and other small and large fish. The crabs have not bothered any of the fish, although my foxface appears to be killing crabs. As long as the crabs are well fed, they shouldn't bother the fish. Also, a few years ago I had a big emerald in a 20 gallon tank with a small damsel. That crab was a bubble algae eating wonder, but never bothered the fish. However, when algae got scarce, I had to start feeding it. After that, each time I walked past the tank, it would wave its claws at me begging for a goody. IME, emerald crabs are smart (and never to be totally trusted, but IME if they go rogue corals are their preferred victims).
     
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  3. demeyer2

    demeyer2 Active Member Build Thread Contributor

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    Thanks! This is what I was hoping to hear. In the event my tank runs low on food for him, I'll move him to my refugium or I'll feed him separately.
     
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  4. Eric Finney

    Eric Finney Member

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    I had one in a 40 breeder. He never bothered the fish (firefish, gobies, clowns, basslets, etc.) that I had in the tank. I never observed him eating any bubble algae that I had in the tank though. I did however witness him picking at stylo's, pocillopora's, and bird nest corals. The tank was fed heavily, in my opinion so I find it hard to believe he wasn't eating well. I am assuming I just had a rogue, as everyone else seems to have good luck with them! Needless to say he now resides in a fuge.
     
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  5. Chris1081

    Chris1081 Member

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    I have had a few over years and never had a problem with them attacking fish or anything and they had cleaned up bubble algae issues I had before. They have pinched my finger though lol
     
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  6. chipmunkofdoom2

    chipmunkofdoom2 Always Making Something R2R Supporter Reef Squad R2R Excellence Award Article Contributor

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    I'm always skeptical when I see threads claiming that an emerald crab has attacked, captured, killed and eaten a completely healthy fish. Emerald crabs are an inch or two wide, at most. They have flat claw tips for picking and eating algae. They're opportunistic, sure, so they'll eat something that's gravely ill or dead. But to catch a live, healthy fish? Especially when a lot of the fish we keep are larger and faster than an emerald? I just don't buy it.

    These animals aren't mantis shrimps or bobbit worms... they're tiny herbivorous crabs. They're not going to ambush and take down a healthy fish much larger than themselves. The only exception I could imagine is if the fish is unusually small and the emerald crab is unusually aggressive, but I would imagine these exceptions are quite rare.
     
  7. nautical_nathaniel

    nautical_nathaniel Indecision may or may not be my problem. R2R Supporter Reef Squad Leader R2R Excellence Award Build Thread Contributor Article Contributor

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    Only issue I've had with emerald crabs is them picking zoas off of their rock. They don't eat them, but the act of picking them off and then sending them floating around the tank is super infuriating.
     
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  8. AdamNC

    AdamNC Lawnmower Blenny says nom nom R2R Supporter R2R Excellence Award R2R Secret Santa Build Thread Contributor

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    I’ve had them before raise their claws to some but appeared in a way of saying “hey get away from my spot”.
     
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  9. TonapahNorth

    TonapahNorth Reefed In R2R Supporter Build Thread Contributor

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    I had one eat a starfish ... completely
     
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  10. Neo Jeo

    Neo Jeo Valuable Member R2R Supporter R2R Secret Santa Build Thread Contributor

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    You need to add a poll for eating corals. I found mine eating a sponge then a coral. I put him into the sump.
     
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  11. Heuristic

    Heuristic Member

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    I agree with others, I don't believe stories about them killing fish. I think most of the time that fish got sick and died without the owner knowing and the crab took advantage of a nice meal. That said, corals can be fair game with them if they're hungry.
     
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  12. mckinney0171

    mckinney0171 Active Member

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    They are totally safe. Except with each other. The males can be very territorial and will dual to the death if one breaks the others territory. They clean around corals and some think they are eating them but they are just cleaning around the coral and not eating any polyps (unless the polyp was already dead of course). Mine defends his birds nest and it is a good symbiotic relationship for both.
     
    Last edited: Apr 16, 2018
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  13. frcarvajal

    frcarvajal Active Member

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    My emerald crab once ate my whole colony of clavularia coral, and to be honest, my clavularia was bothering me invading my acroporas rock so he went and ate all the clavularia. I am happy with that decision he made, I would say we are really connected!
     
  14. Justin Merritt

    Justin Merritt Active Member

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    Had one take a nice big chunk out of a beautiful dragon soul Favia.... back to the lfs it went! I try to stay away from most crabs these days.
     
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  15. Xandernfs

    Xandernfs Active Member

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    I, ironically, got 2 emerald crabs for my Reefer250 yesterday. I added a piece of LR and it has hair and bubble algae on it. I'm hoping they will take care of it. If not, oh well. I like watching them and they add some diversity to the tank.
     
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  16. Robg719

    Robg719 Member Build Thread Contributor

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    I used to have 2. One was fine with fish and corals, the other used to pick apart my leathers so he got voted out of the tank
     
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  17. Yati

    Yati Active Member Build Thread Contributor

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    I have 4 in my system now.. I rarely see them but when I do they are mainly picking off the rock...
     
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  18. jda

    jda Valuable Member

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    Where you get them matters. I have never had any issues from specimens from the Florida Keys. Details matter here, IMO.

    The will stay in the shadows and eat the bubble algae that you cannot see first. Then, they will wander out into the open. As the bubble algae begins to dwindle, make sure that there is enough food to feed them - they cannot live on detritus.
     
  19. james983

    james983 Active Member

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    IMO. Emerald crabs are not capable of catching a healthy fish. On the other hand, have often seen my fish stealing from my Emerald crabs without much of an issue.

    I do think it’s a good practice to target feed them if your tank is barren of algae. I always give mine guys a piece of sheet algae whenever I see one out and about.
     
  20. jda

    jda Valuable Member

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    I, personally, have no interest in eating coral. I might, however, if you starve me for a few weeks. Think of any reef-safe invert story that goes bad in this light... peppermint shrimp too.
     
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