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Sometimes one fish dies, without any apparent disease. In previous aquariums I would always remove them as fast as I could.

Now my aquarium is a bit bigger, and I have some laziness to remove those bodies: they are too deep, or in the back, or partially eaten. So I decide to leave some, and they tend to disappear in a few days.

Are there any safety issues by doing that? Will other fish die if they eat dead fish? Will they develop some mad fish disease?

Sometimes, after you have established an aquarium, with everything working as it should, fish might die simply because it gets old, or have a shorter life-span due to its condition before being sold to you, or because some other fish had a fight with it.

If only one fish died, without white / black spots, no sign of fungus or parasites, no alteration in the gills, I usually rule out diseases or environmental problems.

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  • We recently had a guppy die a couple days after we bought it, yet we never found the body. We do have small pond snails and the ammonia levels were 0, so I assume the snails cleaned it up. I try to remove a dead fish immediately. I have no idea how long it would take after it's death to toxify the aquarium. I really would like to know. I assume the size of a fish might have something to do with it. – user6274 Dec 11 '15 at 22:17
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Assuming you're absolutely certain that the fish did not die from a disease or parasite (I'm not certain how you would ensure that, short of having absolutely nothing new introduced into the environment for an extended period of time prior to the death)...

I would say it depends upon what died, and the other denizens of your aquarium.

If you have a decent Clean Up Crew that will rather quickly consume the body, you're probably not going to run any serious risks of the body releasing enough toxins to jeopardize the other fish.

If you lack sufficiently voracious cleaners, or your dead fish is on the largish side, you should pull it out of your tank sooner rather than later, though.

Generally, at least among saltwater tank owners, leaving a dead fish for the CUC doesn't seem that uncommon.

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Like any other protein-based life form, dead fish give off toxic byproducts like cadaverine and putrescene, which can be toxic in high doses. I can imagine that it's not urgent that you remove the dead fish, but letting them fester and degrade away may have toxic effects on the other fish. I don't have a reference to back that up, though.

This article talks about their toxicity to humans when consuming fish with high levels of these compounds, so I would imagine with a much lower weight, the fish would acquire toxic levels much more readily and quickly.

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You should not. How could you be so sure that the fish died a natural death? I mean, if it was due to some disease then it could be spread if other fishes eat the dead body. And if it's due to some natural death it will still be a risk of water pollution through the dead body degradation process. It can make water toxic, so why take that risk with your beloved fishes?

And it's important to know the cause of death, if fishes are dying it could be due to a high amount of ammonia in water or any toxic parameter. So always take precautions for the loved ones.

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In my 200 L fresh water tank, which is an aggressive tank, fish occasionally get harassed to death. I let the other fish eat the dead but take it out if it's still there after a day.

Dead snails on the other hand have seemed to have cause major apocalypses in the tank over the years so now I always take them out immediately.

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