What could kill small fish?


New member
I have a tank that has been set up for a couple of months now. It is a 29 gallon and has around 20 pounds of live rock. I have had my yasha goby and a guppy disappear during the night. I haven't found a body or anything. My only guess is, something must be eating them. I'm going to stick another guppy in the tank and see if it disappears. I have had the guppies in this tank as long as it has been set up, so they are fully acclimated to the tank. They usually sleep at the top of the tank, but I got sick of having them in the display tank and stuck all but one in the sump. The one that was left was more reclusive since she was alone and started sleeping under the rocks near the bottom. I have a yellowhead jawfish and a very small candy cane pistol shrimp left in the tank. I'm very worried about the shrimp. I fear he could be next on the menu.
I did randomly pull out a small rock and put it in the sump. Unknowingly, there was a small mantis shrimp in it. This thing is super load so I'm guessing if I had more in the main tank I'd hear it? How big do mantis shrimp need to be in order to take out small fish? The one I accidentally found is the size of my thumb. He is super loud, too. Much louder than my pistol shrimp. So far, I only hear clicking coming from my sump. My pistol shrimp rarely clicks but I know he's still there because I see him occasionally.
I have seen red worms that I was thinking were bristle worms? And something that I think is a very little brittle starfish? Other than that, I don't see anything else but I haven't looked at my tank at night. Is there anything I should be looking for? I'd like to replace the goby so my shrimp isn't alone and I was hoping to get some sexy shrimp, but I need to figure out why my fish are disappearing.


New member
My guess would be the mantis shrimp. did all of your rock come from the same place? Mantis shrimp don't need to be all that large to take out fish. I had a small one that took everything out of mine.


-RT * ln(k)
The pistol shrimp may be next, or if it is like the one I had it may be the perpetrator.


New member
I got my rocks from different places. I very recently added some new rock and that's when things started disappearing. I would think that if they are dying, I'd see a body floating around. I'll have to look around again and see if I see anything in the rock. Maybe set a trap and see what shows up? I can pull out some rock, but not all because the bottom rocks are half under the sand and half on top. I am pretty positive that it wasn't my pistol shrimp, because the goby and pistol lived together and the shrimp is smaller than the goby. Also, this mantis shrimp was in the sump when my guppy disappeared so it wasn't this one.

Sugar Magnolia

Mother of Dachshunds
Staff member
RC Mod
Bait a tall, smooth sided glass with a smal piece of raw shrimp and tilt it against the rockwork. Xanthid crabs are nocturnal so it'll go in after the food but won't be able to climb back out. Usually only takes a night or two to catch it if it is a crab.


New member
Also, what do I do with this mantis shrimp? I don't have the heart to kill it, but its keeping my husband and I awake at night!


New member
I would see this guy every day. He was not shy at all. If he was in his burrow, all I'd have to do is put some food in the tank and he'd come shooting out to eat. The jawfish has disappeared for a few days, but the yasha I would see every day. Even the shrimp disappears for days at a time but never the yasha. It's been six days since I last saw him. I started getting worried after day three and knew he was gone when I saw the shrimp fixing his tunnel alone that same day. The yasha and the shrimp are always together. There aren't any coral out there that eat fish are there?
Also, I've read that if you bring a mantis shrimp to the pet store, they'd just feed it to their bigger fish. This fish store has a huge selection of saltwater fish and corals and invertebrates, but I've never seen a mantis shrimp for sell there. I guess he can stay in the sump for now. Maybe I'll luck out and he'll turn out to be one of those really pretty mantis shrimp and I'll be able to give him away easily.


Premium Member
Lots of pics out there of corals eating fish. There was a thread the other day where an acan had a harlequin shrimp's tail but it managed to get out. I've seen pics of anemones, brain corals, acans, hairy mushrooms, and even a couple of clams that had fish sticking out of them. Most times the people didn't see the incident so didn't know if an otherwise healthy fish died and the coral caught it or if it caught the living fish. The clams always caught the living fish, closed on it reflexively when they stuck their heads in it.

It takes quite a while for a coral to digest something that large, so chances are you would have seen that depending on the size of the coral.

What kind of pistol do you have? It's not uncommon for some kinds to kill the fish they're paired with.

My money would still be on a mantis if you know you have one.


New member
You could try moving rocks down to the sump untill the clicking sound has moved. Even if he is not in the rock works you would be able to see where he is once sand is bare.