What do you do when a fish goes missing?

ErikVR · Oct 17, 2023

Hi all,

I'm wondering, what do you do when a fish goes missing? A few months ago I was missing a goby that I found on the floor beneath a cabinet after a few days. But what if you are missing a larger fish that you can't seem to find anywhere and the only conclusion is that it died somewhere in the tank?

Do you accept it and hope that the bacteria can handle it breaking down somewhere in your tank? Or do you tear down the rockwork to find it?

blecki · Oct 17, 2023

It depends on the size of the fish and the size of the tank. Unless it's a large tang, if I don't see it die, by time I realize it's missing there's quite literally nothing left.

ErikVR · Oct 17, 2023

Is there a situation when tearing the rocks down is better than letting it break down? Let's say an 8 inch tang in a 200G tank?

vlangel · Oct 17, 2023

ErikVR said:
Is there a situation when tearing the rocks down is better than letting it break down? Let's say an 8 inch tang in a 200G tank?

In an established 200G tank with a reasonable amount of rock, unless your fish is of shark proportions, the tank should absorb it with no problem. I only have a 56G with a 30G sump and even if my tomini tang went into my extensive rockwork and perished, I would not tear it apart to look for it. I do have nassarius snails, a coral banded shrimp to scavenge but even pods will work on a carcass pretty quickly.

JonoH · Oct 17, 2023

Had a large Blue Tang go missing a few months ago, wasnt on the floor anywhere, so ended up draining and checking the overflow and sure enough...managed to jump in there!
Was a massive pain to get it out of there, needless to say, there is a top on that now!

Cell · Oct 17, 2023

When I first notice, I check all the pumps/overflow for a body as well as the floor and surrounding area.

I think a good general rule of thumb is that if its small enough to go completely missing in your tank without a trace, then you probably don't have to worry about it.

ErikVR · Oct 18, 2023

blecki said:
It depends on the size of the fish and the size of the tank. Unless it's a large tang, if I don't see it die, by time I realize it's missing there's quite literally nothing left.

Will it be that quick?
My tangs are always out and about. If I don't see one for a day I'd be certain that it's dead.

taricha · Oct 18, 2023

ErikVR said:
Is there a situation when tearing the rocks down is better than letting it break down? Let's say an 8 inch tang in a 200G tank?

Even in that scenario, the bacteria / clean up crew can break it down fast enough that the decomposing fish is not going to significantly hurt the system.
I wouldn't rip up my rockwork for any dead fish scenario.

couple of years back I had disease kill multiple fish faster than I could act to intervene, so I just measured the tank parameters, the ammonia spike was barely detectable, and never got to a concerning level.

DJF · Oct 18, 2023

Every mystery deserves to be solved but I would draw the line before causing a mini cycle.

ErikVR · Oct 19, 2023

DJF said:
Every mystery deserves to be solved but I would draw the line before causing a mini cycle.

I'm guessing there are differences between the fresh and saltwater world then. If I lost a medium sized African chiclid between the rocks, the tank would go foul after a few days. Big ammonia spike and I could even smell it in the room. And that was a large 200G mature tank as well. That's why I'm so scared to leave a bigger dead fish in my tank.

Also, they would take ages to decompose. You would still find fleshy remains after 1-2 weeks of a fish gone missing.

Jedi1199 · Oct 19, 2023

For what its worth... A dead fish in an established tank would be negligible compared to what would be stirred up by breaking down the rock work. If I don't find a dead fish on the floor somewhere I chalk it up to nature and let nature do its thing.... I do monitor water parameters a little more closely for a while after that happens though and do larger than normal water changes.

DJF · Oct 19, 2023

ErikVR said:
I'm guessing there are differences between the fresh and saltwater world then. If I lost a medium sized African chiclid between the rocks, the tank would go foul after a few days. Big ammonia spike and I could even smell it in the room. And that was a large 200G mature tank as well. That's why I'm so scared to leave a bigger dead fish in my tank.

Also, they would take ages to decompose. You would still find fleshy remains after 1-2 weeks of a fish gone missing.

Probably so. I’ve got critters living in and on my sand that help break things down.

blecki · Oct 19, 2023

ErikVR said:
Will it be that quick?

ErikVR said:
Also, they would take ages to decompose. You would still find fleshy remains after 1-2 weeks of a fish gone missing.

There's a lot more life in an established reef tank then even the best planted tank. Granted it was a small fish, but I lost a silver molly in my molly tank two days ago. It took about 12 hours for a couple of bristle worms to completely devour the corpse, and that tank doesn't have any of snails or crabs to speed it along. A dead tang in my reef is likely to turn into a pile of shells and worms in a few hours.

Stevorino · Oct 19, 2023

Depends entirely on the fish.

If it's a small fry that tends to hide, I don't stress but keep an eye out. I've had one or two over the years that 'disappeared' for months to eventually come back out.

If it's a big guy that rarely hides, I will generally stop everything and figure out where he's at.

ErikVR · Oct 19, 2023

blecki said:
There's a lot more life in an established reef tank then even the best planted tank.

Even worse. It was an mbuna cichlid tank. Just sand, rocks and fish.

ErikVR · Oct 19, 2023

Stevorino said:
Depends entirely on the fish.

If it's a small fry that tends to hide, I don't stress but keep an eye out. I've had one or two over the years that 'disappeared' for months to eventually come back out.

If it's a big guy that rarely hides, I will generally stop everything and figure out where he's at.

The thing is that a reef overgrown with corals can't be taken apart. That's why I was wondering how everyone handles it.

Someshmuk · Oct 19, 2023

If its any of my bigger fish go missing, I have to confirm if its dead and not necessarily if it died in my tank. I had a foxface pass and it was completely devoured by nassarius snails, hermit crabs, and bristle worms. Even my tangs were having a piece of it. By the end of the next day, it was nothing more than bones. Nothing left to rot away if its been picked clean.