Guppy Fish and Killifish – Can They Live Together?

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If you love both guppies and killifish equally and plan on mixing them into the same tank, we need to discuss the specifics. As you already know, guppies are relatively friendly fish that will get along with pretty much any other breed. So long as they share similar water requirements, among other things.

The same can’t be said about the killifish. There are some noticeable differences between the killifish and guppies that could prevent the 2 breeds from coexisting peacefully.

Today, we will discuss killifish and guppies and assess whether they can make good tank mates or not.

Are Killifish And Guppies The Same?

No, killifish and guppies are not the same. They are actually quite different breeds, with differences that go beyond the physical appearance.

Here’s where guppies and killifish differ from one another:

  • DietsGuppies are tropical fish who prefer omnivorous diets. They require live food and plants and algae to remain healthy and thrive in the long run. Killifish, however, are carnivores. They want nothing to do with plants, which can spell disaster when mixing the killifish with a friendly and peaceful breed like guppies. There have been cases where killifish have managed to kill and consume guppies twice their size. You can see the problem here.
  • Size difference – Killifish belong to multiple families, including Aplocheilidae, Fundulidae, Valenciidae, etc. There are over 1,200 species of killifish available, each coming with its own specifics. The killifish can vary in size from 1 to 4 inches, while most guppies can only reach 2.5. This will quickly transform guppies into prey, dealing with carnivore fish species that are twice their size.
  • Territorial behavior – Guppies males will show some territorial behavior, but only limited and only in relatively overcrowded tanks. Killifish, however, will spike the intensity tenfold. Killifish males tend to be very territorial and aggressive, both towards one another and towards other fish species. This can quickly spell disaster in a mixed tank where you have more than 3 killifish males.
  • Tank requirements – The standard recommendation for tank size for guppies is one fish per 2 gallons of water. A 20-gallon tank should hold no more than 10 guppies. The same numbers don’t apply to killifish. In their case, the official recommendations are one pair for a 20-gallon tank. You should ideally only have 2 killifish for a 20-gallon tank. If you want to add guppies, you should get at least a 40 or 50-gallon tank to avoid overcrowding and drop the risk of aggression.

As you can see, we’re already on dangerous territory. Killifish and guppies already seem incompatible, and we haven’t even started yet.

Are Killifish Good Tank Mates For Guppies?

I will say no right from the get-go. But here’s the deal. Many people have mixed killifish and guppies successfully with minimal fallout. To do that, however, you should consider several precautionary measures:

  • Ensure adequate room – As I’ve mentioned previously, one killifish requires at least 10 gallons of water. Guppies require less water volume, which means that, when choosing the tank, you should primarily keep track of your killifish’s requirements. Ensure enough room for both species, and you might be able to minimize the killifish aggression.
  • Control the number of killifish males – Killifish males are more aggressive and territorial than females. The best idea would be only to have female killifish, which will contribute to a more stable tank environment long-term. On the other hand, having more females will also increase the number of fry to expect in the reproductive season. I think that you can live with the latter, which is why I suggest focusing on the former.
  • Manage your killifish’s diet adequately – The killifish prefers to eat arthropods, worms, and insects as part of its carnivore diet. Providing the fish with adequate food will diminish its killing instincts. I suggest ensuring adequate live food daily and feeding the killifish separately from guppies if possible. There are plenty of fish food options to consider, both homemade and commercially bought. You can even have homemade live cultures of different arthropods and worms if you have the time and patience for that.
  • Choose the killifish species carefully – You have around 1,270 species of killifish to choose from, each coming with its unique characteristics and temperaments. Some are more aggressive and territorial than others, while others are bigger and more imposing. I suggest choosing a species of killifish that’s closer to your guppies’ conformation. Rely on a smaller killifish species with a calmer and friendlier temperament to minimize aggression and stabilize the tank dynamics.

Will Killifish Eat Guppies?

Not always, but sometimes they do. It all depends on a handful of factors, including the size difference, the species’ aggression, tank conditions, etc. There is a lower chance for your killifish to attack guppies if both species are of similar size. That doesn’t mean it can’t happen, especially if the killifish doesn’t get enough food.

However, you should expect an entirely different situation when it comes to guppy fry. Your killifish will consume the fry as soon as they’re born. If you want them to survive, I suggest moving the pregnant female guppy into a different tank when the labor sets in.

I guess you can make the situation work with a few tweaks here and there. If you were to ask me, however, I would advise avoiding mixing the 2 species altogether.

Will Guppies Eat Killifish?

The chances for your guppies to eat killifish is very low. Guppies will typically only attack smaller fish species, and the killifish are similar in size. Guppies will eat the killifish fry, however, since they’re smaller and pretty much defenseless during their first weeks of life.

Other than that, guppies have no interest in other fish species, primarily because they don’t typically exhibit predatorial behavior. They will be content with their typical omnivorous diets so long as they have enough food throughout the day.

Can Killifish Live With Other Fish?

They can, but barely. Some killifish species are more temperamental than others, making it difficult for them to coexist with any other species. It all comes down to selecting a more peaceful breed that shows less aggression and territorial tendencies.

This is that much more important when discussing tank mates options for your guppies. Guppies are friendly and easy-going and can become victims of bullying and aggression fast. It’s imperative to find them tank mates with similar personalities, environmental preferences, and dietary habits.

Can Guppies Live With Other Fish?

Yes, guppies can live with other peaceful fish. The key aspect to note is compatibility. Guppies will tolerate a variety of other fish species, including tetras, platies, mollies, swordtails, etc.

You need to make sure that your guppies share similar dietary, environmental, and temperamental preferences and inclinations. Guppies don’t display predatorial behavior, especially towards breeds similar in size.


Guppies and killifish are 2 very different breeds with different needs, temperaments, and buildups. While some breeds of killifish can live with guppies in relative peace, others are completely incompatible.

If you insist in trying your luck with mixing the two species, at least look for a smaller, less aggressive breed of killifish. This will minimize the chance of aggression and territorial display in the long run.

Updated: November 10, 2021
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