What to do if you find a dead fish in your tank


Suddenly discovered a tragedy in your aquarium and not sure how to handle the situation? Here are five tips to help spot any problem and hopefully prevent more casualties.

1. Observe

Check your fish every day when feeding them and do a quick head count and health check. Are they all there? Six Neons, three Corydoras? Are they all doing what they should be?

If a fish is missing check the corners of the tank and open the hood to find out where it is, as any hanging around by the filter instead of with friends is a bad sign.

You may not be able to see the missing fish at all. If so, step up your search and assume it is dead. Depending on species and length of decomposition, the corpse could be stuck to filter inlets, floating at the surface, lying on the bottom, under décor like rocks or wood or caught in plants.

Check all areas until the fish is found. If it’s dead, move to step two.

2. Remove

Any dead fish should be removed, as its body will quickly rot in the warm, bacteria-laden water. A corpse will pollute water, risking the health of other fish in the tank.

If it died from disease the last thing you want is other fish consuming its body parts, so remove immediately.

3. Examine

If you have found the corpse quickly enough you may be able to give it a quick once-over diagnostic check.

Are the fins intact? Ragged or split fins and scuffed skin may mean the fish was bullied or beaten to death, as is often the case with Malawi cichlids.

Is the body bloated as in the picture of the goldfish above? This could indicate an internal infection.

4. Test water

Every time you find a dead fish you must test the water to check everything is OK, as water quality, or failure of it, is the biggest cause of fish deaths. Test water straight away and be prepared to remedy it if anything rears its ugly head, like ammonia.

For an emergency water change, arm yourself with a syphon and bucket, dechlorinator, thermometer, filter bacteria booster and, of course, a test kit that tests for ammonia, nitrite, nitrate and pH.

5. Seek advice

Water test results will go one of two ways. They will either indicate fine, in which case you must look at other causes, or they will alert you to a water quality issue that in itself will need addressing.

If the water is fine you need to look at other factors like disease, starvation, long-term stress through inappropriate conditions, like softwater fish in hard water, or the least likely, but still possible, old age.

If it was part of a species group in your aquarium what are the other fish looking like? If they are OK this is a good sign. If they are all acting differently or looking decidedly ropey they might soon be dead too.

Write down the results of your water test, along with all the other details of your tank, like tank size, filter model, time set up and food, and consult an expert.

Is it playing possum?

Be wary that some catfish like to wedge themselves into tight spaces, making it look like they’ve become trapped and have died.

Humbug catfish in particular do this, and many have met their fate by being removed along with their wooden home.

What’s the best way to get rid of the fish corpse?

Flushing is tempting and quite hygienic, though we doubt your local water board will appreciate various exotic fish species potentially blocking their soil pipe network.

There may also be a disease risk to native species via the waterway too, so don’t do it.

Binning is an option, though hot days will mean an awful smell, flies and maggots. Seal the corpse in a polythene bag to avoid this — though the smell will still escape!

Burial is safe and may be a good option for larger fish to avoid rotting corpses in bins. Incineration via bonfire is also possible, though you will then be left with debris.

How many deaths are deemed acceptable in a community tank?

It depends on how many fish you have and what they are.

Generally, small fish like Neon tetras and smaller are quite short lived, whereas large catfish and cichlids are long lived.

So if you have say 50 assorted small fish, all added at different times, you may lose a dozen a year for various reasons.

It’s when you lose several of them at once, or different species at once, that the alarm bells should start ringing loudly.

When can I restock with fish after any deaths?

It depends on what the cause of death was. If the water quality was perfect and all other fish, including members of its own species, appear OK and look free of disease you could restock within a week.

Leaving it for a full seven days is best, as if others die within that time you’ll know there’s an underlying problem.

Don’t be tempted to restock and add lots of others, as this in itself can cause a water quality issue. Add a few fish each week and observe behaviour.

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