Will Dead Fish Help Cycle Tank, Or Will It Hurt The Tank?

Last Updated on December 26, 2021 by cmoarz

People have come up with some really unique and interesting ways to help cycle an aquarium and jump-start the beneficial bacterial process. Some of those are incredibly effective and some or a bit misguided, But what about a dead fish? Will a dead fish help cycle a tank? Or will it do more harm than good?

Will a Dead Fish Cycle a Tank?

While looking around I came upon an interesting question posed by a newbie to the hobby. He was interested to know whether using dead fish would help cycle an aquarium.

We all know you need ammonia to start a cycle, and dead fish certainly put off a lot of ammonia.

To that degree, Yes, A dead fish will cycle a tank, But honestly, it’s a terrible idea. I do not recommend you do this. Especially if it’s not a fishless cycle.

Think about it for a moment – Even if you did end up cycling the tank successfully with a dead fish, Now you’ve got dead fish soup in an aquarium. This poses some problems.

For one, Dead fish give off a lot more than just ammonia. All sorts of deadly bacteria can bloom from those decaying carcasses.

The water quality, while cycles, would almost certainly crash in quality faster than you can say “Oy that stinks”.

Speaking of stink, the dead fish will certainly not improve an aquarium’s smell. In fact, Trying to cycle a tank with anything dead will make your entire room smell like death for some time.

There are very few smells in the world that are worse than a dead rotting fish in an aquarium full of dead rotting fish goop.

And finally, as if you needed another reason. Could you stop at only one dead fish? Cycling a tank fully takes months. One fish isn’t going to cut it. Chances are you are going to need to replace that nasty carcus a few times over the period of weeks.

Where are you going to get more dead fish with such convenience? Supply aside, That means diving your hand or net into that nasty tank water to retrieve your hunks of rotting fish.

For all these reasons and more, It’s not a wise idea to use dead fish in cycles. Truly it isn’t. Especially if you aren’t doing a fishless cycle. This will almost certainly kill everything else in the tank.

(PS never use ammonia cycling on a none fishless tank)

Cycle Your Tank Properly Instead

You can buy ammonia very cheaply. In bulk no less. There’s no reason to use a dead fish to produce the ammonia when it’s so widely available.

Not to mention most guides and timetables for cycling a tank will be relying on such bottled ammonia for fishless cycling.

Many people have been opting to do fish cycling lately. That’s where you cycle your tank with fish in the aquarium and allow their poop to be the ammonia generator and bottled bacteria for the catalyst of bacteria – The cycle.

Whichever method you decide to use, I suggest you avoid utilizing a dead fish. In the end, it’s just a pointless chore that sounds fun but is in truth horrendously dirty, Smelly, and can have disastrous results if not done correctly.

But it would work, I guess.


Owner of AquariumGravel.com and also owner of actual Aquarium Gravel believe it or not! ;). Setting up beautiful aquarium sceneries and habitats since I was very young. Enjoy!