When Marine Fish Mysteriously Disappear

Blackear Wrasse (H. poeyi) hide in sandy substrate when frightened

Blackear Wrasse (H. poeyi) hide in sandy substrate when frightened

You’re strolling past your marine aquarium, minding your own business, when you notice that something is amiss. The [insert name of fish here] that invariably comes right up to the front of the tank whenever you enter the room is nowhere to be found. You scan every inch of the tank, lift up every chunk of live rock, and even search the floor all around the aquarium, but you still come up empty. It’s as if the fish just vanished into thin air.

What gives? Alien abduction? Chupacabra? Sasquatch? The Rapture? Actually, there are always perfectly simple explanations for such “mysterious” fish disappearances—and only rarely do they involve Sasquatch.

Here, in no particular order, are the most likely scenarios:

It’s in the rockwork

Yep, I know you’ve already torn apart your aquascaping, but look again! Some fish—especially very slender or laterally compressed species—can fit into surprisingly small holes or crevices in rocks, and they aren’t necessarily going to bail just because you lift up the rock they’re hiding in. Heck, some hobbyists even find stowaway fish in newly purchased live rock!

I’m reminded of a flame angelfish I once had that performed just such a disappearing act. After extensive searching and head scratching, I finally discovered the darn thing tucked into what could best be described as a thin “pocket”—rather like the breast pocket on a shirt—on the underside of a rock.

It’s in the substrate

It’s perfectly natural for some fish, for instance, many of the wrasses (e.g., Halichoeres spp.), to bury themselves in the sand when they’re sleeping at night or want to escape danger. In fact, it’s not unusual for newly introduced wrasse species that are prone to burying themselves to remain out of sight in the substrate for several days before finally venturing out in the open.

It jumped

Jumping fish don’t always remain in the precise spot where they initially hit the floor. Still-lively specimens can flip-flop their way into all kinds of unusual places, sometimes a fair distance from the aquarium. Also, family pets—perhaps finally getting their wish—aren’t above carrying off/outright consuming “windfall” fish.

It’s in the sump, refugium, overflow…

Of course, not all jumping fish end up on the floor. Oftentimes, they manage to flip themselves into other water-filled compartments in the aquarium system, such as a sump, refugium, or overflow chamber—which is good because they usually have a pretty good chance of surviving such misadventures.

It was eaten

The obvious suspect in this case would be any larger, predatory fish sharing the same aquarium, but the culprit could also be a predatory crustacean (such as a stowaway mantis shrimp or crab), a fish-eating brittle star (Ophiarachna incrassata), or even one of a few known piscivorous sessile invertebrates, such as the elephant ear corallimorph (Amplexidiscus fenestrafer) or one of various and sundry anemones.

Of course, the fish could also have simply died from other causes and been scavenged by the resident cleanup crew. In a well-established system with a healthy scavenger population, this can happen surprisingly rapidly.

What’s your strangest story?
So, fellow salties, what’s the most mysterious “disappearing act” you’ve ever witnessed—or what’s the oddest place you’ve ever found a “vanished” specimen? Let us know in the comment section below.

Photo credit: Kevin Bryant


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About Jeff Kurtz

Jeff Kurtz is the Co-founder/Editor of Saltwater Smarts, former Senior Consulting Editor for Tropical Fish Hobbyist Magazine, and the aquarist formerly known as “The Salt Creep.” He has been an aquarium hobbyist for over 30 years and is an avid scuba diver.


  1. Paul Baldassano says

    I don’t have any mysterious stories other than Sasquatch and you already mentioned that. I have found Sally Lightfoot crabs 3 rooms away from the tank but I always found them, dead, but found.
    In my tank I find nothing, but it is not mysterious at all. In any older tank the resident population, and sometimes the dominant population is bristle worms. And bristle worms can grow to a foot long and never be noticed. These will make quick work of any dead or weakened fish and if you have a foot long bristle worm, even the fish in your refrigerator are at risk. It’s ten oclock, do you know where your dog is?

  2. Well… It wasn’t a fish… But way back in the mid 1980’s I had a pet octopus…

    Once while I was working on his tank he climbed out. I found him across the room hiding in a shoe.

    He survived his escape and journey without a hitch!

    • Jeff Kurtz says

      Makes you wonder what was going through the octopus’s mind as it traversed your floor–“What the heck kinda tide pool is this?” Thanks for sharing, Rob!

  3. I had a pair of teenie tiny Picasso Clownfish dissappear on day 2 in our 72 gallon reef tank. My wife was devastated as she had wanted them since she discovered Picasso clowns on our initial dive into saltwater the year before.

    So I returned to the store and purchased a second pair. The next week while doing my weekly chores I found that they had somehow ended up in the sump.

    That’s how I ended up with my second tank. 🙂

    • Jeff Kurtz says

      That’s too funny, Mike! It also gives me some ideas on how I can talk my wife into additional tanks!

  4. Matt Bowers (Muttley000) says

    I have a 29 with 3 firefish. I have finally stopped moving 2 of them from my sump back to the main tank, and have resorted to feeding them their. I must have moved them half a dozen times before admitting defeat.
    After moving a tank once I found 3 dried up peppermint shrimp by the wall, I just thought something in that system was eating or killing them.
    Lastly I had a red scooter blennie that would disappear and reappear from time to time. It happened he would bury himself in the sand with only his eyes sticking out behind the rock work.

  5. Evelyn Salas says

    I’ve had the following fish disappear: mandarin, 2 esquisite wrasse, powder brown tang, yellow tang, 2 red dragonette. I’ve also had some coral disappear. The next thing I am going to do is empty the 80 gallon tank and do a fresh water dip. I am losing expensive fish!

    • Oh, my! You’ll definitely need to get to the bottom of whatever is causing so many specimens to disappear before introducing any more livestock!

  6. Evelyn Salas says

    How do you recommend that I look in my live rock for predators. Some of my rock have coral attached to them and it is not easy to remove the coral. How can I do a fresh water dip on rocks that have coral on them?

    • Have you had a chance to look at the tank with a flashlight well after dark? That’s the best time to spot hitchhiking crabs, mantis shrimp, etc. If you can lay eyes on the culprit and figure out where it retreats to, you might be able to narrow down the location of its lair to a few or only one rock. In that case, it’s much easier to either trap the critter or systematically remove the rocks.

      Many corals can tolerate a brief temperature-matched freshwater dip with no problems, but depending on the location/growth habit of the specimen, it may be possible to dip just the rock its attached to. Another method that doesn’t involve submerging the coral is to squirt soda water directly into the predator’s hidey hole if it can be located.

  7. I brought a sweet lips put it in my tank with my puff powder blue trigger clown and two dats later the sweet lips has vanished been through the tank moved all the Rock and plants and it is nowhere to be seen. Any one got any ideas as to why

    Cheers Tim

    • Jeff Kurtz says

      Hi Tim! In cases like that, my first suspicion is that the fish may have jumped out of the tank. Have you looked thoroughly all around the vicinity of the tank (and even beyond)? I’ve had jumpers flip themselves into the strangest places!

  8. I have a small tank, just 10 gallons. I have (or had!) 6 fish – 2 neon tetras, 2 balloon belly mollys and 2 guppies. I also have a ghost shrimp, ADF, and an apple snail. the apple snail is new, we had one that died last week. we also have a small population of ramshorns that I keep in check. all of our fish are very active, I see them all bustling around constantly. we battled ich a couple months back, so I definitely know what sick looks like. Last night, I went to bed at 12:30 am and woke up at 7 to take my kids to school. one of the guppies and one of the mollies are completely gone. the molly isn’t itty bitty either, so if it were ailing, I think I would have noticed. the other one is small. just baffles me! But my theory is that our snail that died has come back for revenge. The molly used to pester the snail constantly! so far we haven’t found them. the tank is pretty well closed up except for some space near the filter. no remains found! It may drive me crazy wondering what happened.

    • Jeff Kurtz says

      Hi Jill! My suspicion is that the fish died of other causes and were then opportunistically scavenged by the apple snail. Just my best guess!

  9. Hi Can anyone help. My fish have disappeared. New ones too.
    Then a mysterious ‘thing’ appeared apparently attached to a rock.
    It’s about 3 inches in height and opaque. My imagination may be taking over
    but it looks as though it has a white mouth at the top and lower down there are white
    ribs? then lower possibly an anus. Maybe I’ve been watching too many movies.
    Has anyone any ideas?

  10. Hi The strangest thing happened i came down this morning and my tank had gone, could not locate it anywhere not even the sump, or stand. It was not till later that day i realized i was in the wrong house, i did return home and on a serious note my cleaner wrasse has died in a lump of live rock. Any suggestions on the phosphate build up within the tank its about 400 ltr trying to get the thing out is not an option as it holds up my whole aquascape? no bristles

    • He he! Usually when a whole tank disappears, a spouse or significant other is implicated. (Their way of saying, “We’ll see if another dollar gets wasted on this thing!”) Anyhow, your best bet with respect to the rising phosphates after the cleaner wrasse’s disappearance is to step up water changes until it has completely decomposed, which shouldn’t take terribly long for a relatively small fish.

  11. Hi, so 3 weeks ago we caught a semi pommi and a blue surgeon, well they both have been eating well and thriving in the tank, but both just vanished, looked alll over in the tank there are no bodies any where in the tank, any sugestions?? I have t moved rocks to check as the tank is too high for me to reach, my husband said he doesnt want to move rocks around and disturb the rest of the fishies, i have put the chaser in the back to see if they come out by chance but no fish coming out of hiding.

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