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What is a Killfish?

Alex Paul
Alex Paul

There are over 1000 different species of killfish belonging to a number of different families. The vast majority of killfish are small and range up to approximately 2 inches in length (5 cm). As there are so many different types of killfish, the group has a large range, with species found in Africa, southern Europe, and America. All species are oviparous, which means that the mother releases undeveloped eggs. Most species have interesting colorings and are also easy to keep in aquariums, which is why they are popular as pets.

The largest family is Rivulidae, which contains over 300 species. There are a number of other families, such as Valenciidae, Aplocheilidae, and Cyprinodontidae. In some areas, the term killfish is used to describe any fish which is part of the Cyprinodontidae family, while in other regions it has a much broader meaning.


In general, killfish are small and grow to a few inches. There are, however, some species which grow larger. The biggest species grows to about 6 inches (15 cm) in size. This is another reason why the fish are regularly kept in aquariums; they require less space when compared to many other types of sea creatures. Typically, the fish will live for about two years.

The range of this type of fish is large, as different species are found in waters on most continents. Antarctica and Australia are the only two continents where no species can be found, but Northern Europe also lacks any killfish. Most species live in lakes and rivers, but there are others that have adapted to more temporary areas of water such as flood plains.

All killfish are oviparous, which means that they lay eggs. To be classified as an oviparous fish, the mother must release the eggs before any significant development has occurred within her. Most, but not all, fish lay young in this way.

Killfish are known for being easy to keep as pets. The fish can adapt, and even breed, in an artificial environment with few problems. A potential issue with some species is that they can become aggressive with other species, so it’s important to mix the fish carefully. Most species have bright colorings which makes them especially attractive to fish enthusiasts. A particularly common species is the Golden Wonderor, also known as Striped Panchax, which can often be found in pet shops as well as specialist aquarium fish dealers.

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Discussion Comments


@alex94: I have Killifish in my tank and we culture our own fruit flies, mosquito larva, and white worms as they are all very beneficial to the fish. The Blue Gularis killifish is particularly beautiful can reach a size of 6 inches and are sometimes considered too big for a small tank.

They are interesting community fish but can be very territorial. They are usually best kept with their own species. You also don’t want them to interbreed with other species. Killifish can also jump up to a couple of inches so don’t leave any gaps in your tank. Many people refer to Killifish as Killies.


Are we talking about "killfish" or "killifish"? I have never heard of killfish. However, I have killifish in my aquarium.


@alex94: Many people are attracted to Killifish for an addition to their aquarium. They have very attractive in color and they have unique personality. They are very easy to take care of. They do not grow very large so they are great for tanks.

They need water that is acidic and the water should be conditioned with a PH between 5.5 and 7.0. If your area has hard water then you might want to add a piece of driftwood to lower the PH levels. Driftwood is a natural stabilizer. It might give your water a brownish tinge and it won’t harm your fish.


What do I need to know about a killfish before buying them to put in my aquarium? The name is kind of unsettling! Will they eat my other fish?

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