What is the Best Practice for Culling Guppies?

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Guppies are the most popular aquarium fish for good reasons. They display astounding color and pattern variety, are hardy and adaptable, and are generally friendly and peaceful.

But there’s one other factor that leads people to prioritize guppies over most other fish, and that’s their breeding prowess.

No fish is as effective as guppies are in this area. It’s why guppies are some of the main feeder fish used as nourishment for other aquatic species.

But what to do if you don’t want them to breed? Sure, you can separate the males from the females, but accidents can happen.

Not to mention, guppy females can store the male’s sperm inside their bodies for up to 10 months and use it to self-impregnate each month. So, you’ll get a lot of guppy fry whether you want it or not.

Today, we will discuss the culling of guppies. How do you get rid of the fry in a humane way? Because truth be told, there are a variety of inhumane ways to get rid of them. But we’re not about that here.

5 Ways to Humanely Cull Guppies

To be noted, by ‘cull,’ we don’t mean kill necessarily. There are ways of disposing of your guppies without killing them, and we’ll dive into the most widespread ones today.

So, you have too many guppy fry due to the fish’s unhinged breeding. Here’s what you can do:

Use as Feeder Fish

This is the most obvious and useful method of disposing of your unwanted guppies. Guppies can multiply fast, as guppy females deliver up to 200 fry during one spawn. Even more in some cases.

This provides you with the optimal opportunity to use the resulting fry as feeder fish.

The concept is simple. Once the female is gravid, you wait it out until the delivery deadline. Once your female shows signs of contractions, you relocate it into a breeding tank to deliver the fry.

This will improve the fry’s survival dramatically since guppies are known to display cannibalistic tendencies. Adult guppies will eat most of the fry or, at least, the one they can catch.

Once the fry have been delivered, you move the guppy female back into the main tank.

The fry will grow uninhibited in their new environment, and you can use them regularly as food for other fish or aquatic animals.

This method clearly demands you invest in a breeding tank to house the guppies until they are fit for use.

The good part is that the timeframe for that can differ. You can feed them to your fish while they’re still fry or wait for them to grow a bit, in case your predator fish is larger.

Trade with Local Fish Store

This is an interesting option that few people are even aware it’s out there. If you can’t use your guppies as feeder fish and don’t want to kill them, sell them out.

Few fish stores will reject your offer, especially if the guppies are free.

This being said, don’t expect to get much of a profit out of your trades. Most fish stores won’t pay anything or if they will, it will be rather symbolic.

The trade will mostly go one of 3 ways:

  • No money involved – They will simply take your guppies free of charge. Provided you agree to that, of course. Many people do, simply for the wellbeing of the guppies. It’s better to give them away than kill them or have them live miserable, short lives due to lacking a proper setup for them.
  • Store credits – This is better than the former, as the store will provide you with some store credits in exchange for your guppies. You can only use these credits in the store, though. Still, it beats nothing.
  • Buying in bulk – Many fish shops will offer some symbolic sum for a handful of guppies, based on your agreement. Expect something like $1 per 10 guppy fry or somewhere in that ballpark, anyway. This option is more appealing to kids, who get to experience firsthand the notion of making a bit of profit from their work.

Naturally, this method involves more effort since you will first need to find the right shop and take your guppies there.

But it’s worth knowing that other people will be getting your guppies and the fish will be taken care of.

Sell Them Online

This is a more fitting solution if you have some good guppy strains that could be worth money on the market. Professional breeders can profit by selective breeding, allowing them to create rare or even unique strains with a high appeal in the community.

However, you probably don’t fit that category.

You most likely have some extra unwanted guppies that you just want to get rid of. No unique features, nothing worth a lot of money. Even so, it’s worth trying your luck on various marketplaces.

There are many people that won’t refuse some cheap guppies for a change. Maybe they’re getting them for their kids, or they’re looking to get into the aquarium business and need cheap guppies during their learning phase.

Or maybe they need them to start off a feeder tank, and your guppies might fit the profile. Either way, posting an online announcement won’t take much and may pay off. You could be making some people happy in the process too.

Give Them to Friends

This should be your go-to solution if you already have friends with aquariums. They could be using your guppies for a variety of purposes, including feeder fish.

You could even offer them to your friends if they don’t have an aquarium set up yet.

Maybe your spare guppies could convince them to jump into the hobby, so you’ll be gaining a tank buddy along the way too.

Euthanize Your Fish

When all else fails, euthanasia may remain your only valid option. Fortunately, this process also has a humane aspect to it.

So, there are right and wrong ways to go about it. Here’s what I mean by that:

The Right Ways

  • The clove oil method – Clove oil is a substance extracted from the clove oil plant and has many uses, including in medicine. Besides mild analgesic properties, clove oil also has a potent anesthetic effect. The latter makes it perfect for use in fish euthanasia, especially since clove oil is highly toxic in pretty much any larger amount. Around 0.4 mg per liter of water is enough to paralyze and kill fish rather rapidly.
  • The stun-and-stab method – This is a more gruesome killing method involving smashing and stabbing the fish for a certain and quick death. The method itself is rather simple and effective. You remove the fish from the tank, cover it with a cloth or any similar material, smash its head with a blunt object, and then use a knife to pierce through the brain. It sounds awful, but it’s effective, although not quite to everyone’s liking.
  • CO2 poisoning – This is a less shocking method that will also result in certain death. You take the fish out of its environment and place it into a different water container. Then you inject pressurized CO2 into the water for up to 30 seconds to a minute. The excess of CO2 will force the oxygen out of the water, rendering the fish unconscious within seconds. The official death will be asphyxiation. It’s typically painless since the fish will be unconscious for the entire duration.
  • Anesthetic overdose – You can use various anesthetic agents for this purpose, including benzocaine hydrochloride, sodium pentobarbital, tricaine methanesulphonate, or 2-phenoxyethanol. These are generally for euthanizing fish at a vet, so you need to take your fish there first. If that is not possible, or you want to spare your fish of stress, have the vet come to you. The entire procedure will be swift and painless.

The Wrong Ways to Cull Guppies

  • Throwing out the fish – You can’t just throw out your fish and forget about it for 2 reasons. The first is that this is literally the definition of inhumane. The fish will eventually suffocate to death, but the process may last quite a while. During this time, the fish will experience severe distress and will suffer greatly along the way. Not to mention, various animals could stumble upon the fish’s corpse and eat it, risking bacterial infections in the process.
  • Feed the fish to your pets – This will ensure a swifter death but comes with more severe risks as well. Aquarium fish are notorious for containing various bacteria and viruses, most of which are latent, that will pass on to other animals. You don’t want your pets to get sick, so you should never feed them your tank fish, even if they seem healthy.
  • Flush the fish down the toilet – This is the go-to killing method for many aquarists. I suspect that the reason for that is the lack of personal involvement. The stun-and-stab method is far more personal than pressing a button and watching the fish disappear in a whirlwind of water. You almost don’t even feel the impact. The problem is that the fish will inevitably suffer greatly in the process. Its body will also land in the sewage system, filling the area with parasites and bacteria that may find their way to other hosts. It’s even worse if, by some magic, the fish survives the ordeal. Now you have a live fish contaminating the environment and infecting other fish in the process.

I advise sticking to the safer, more effective, and more humane procedures in this sense. It’s the more…humane approach.

Never Release Your Guppies in the Wild!

We could have mentioned this one in the ‘The Wrong Ways’ section, but I feel like this point deserves a section of its own.

Too many people release unwanted guppies and other tank fish into the wild, completely oblivious to the consequences. In their mind, they’re doing the right thing by allowing the fish to continue its life.

In reality, they are damaging the habitat and affecting other fish species and aquatic animals in the process.

Washington state knows this point very well. 2021 specifically ranks as a nightmare year due to the invasion of goldfish wreaking havoc in the West Medical Lake and other areas.

But these fish can’t travel on land, and they can’t fly. So, how did they get there? That’s right, people released them into the wild. The problem with goldfish is that they multiply fast, are very resilient and adaptable, and will eat anything around the clock.

Their presence creates a highly competitive environment to which other fish species cannot adapt to. Goldfish are simply too effective at controlling their habitat.

But what do goldfish have in common with guppies? Well, despite being different species, goldfish and guppies pose similar risks.

Guppies, too, spread fast and can adapt to a variety of environmental conditions, which, in turn, makes them more competitive overall.

A feral guppy population will easily take over any aquatic environment, leading other fish species to starve. Not to mention, guppies raised in captivity and released into the wild risk bringing a variety of bacteria and viruses along with them.

These can eradicate entire fish populations relatively fast since those fish aren’t accustomed to many of the pathogens latent in guppies.

So, whatever you do, don’t release your guppies into the wild, even if we’re talking about healthy fish. You’re not doing anything any good; on the contrary.


Guppies are some of the most exhilarating, beautiful, and adored fish in the aquarium business.

But, sometimes, you simply need to get rid of a few. If you’re not fond of euthanizing them, consider some of my other options.

If it does come down to euthanasia, at least now you know how to perform it more effectively and humanely.

Author Image Fabian
I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.
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