April 2

Killifish – Behavior, Feeding, Care and Breeding Guide


Elegant, colorful, and majestically graceful, killifish is one of the most beautiful types of fish you can find anywhere.

With almost 1,300 species of killifish (you can also call them killies), they all belong to the families of Cyprinodontiformes (a member of the superorder Atherinomorpha) which are mainly tiny fish that dwell in freshwater.

Unlike some other fish in the same Cyprinodontiformes family, killifish lay eggs and are thus called oviparous. It will surely interest you to know that not all fish lay eggs like the killifish, but that is a story for another day. They are also considered to be teleosts, which means that they are vertebrate fishes.

Killifish Location

Killifish species are considered abundant; you will find them almost everywhere on the planet where there are fresh or slightly salty water sources. The only parts of the globe you are not going to see Antarctica (for obvious reasons), Australia, and the countries of Scandinavia like Norway, Sweden, and Denmark.

In Africa, killifish are abundant except for the hot desert areas like in North Africa and parts of the southwestern African region where there are the arid Namib and Kalahari Deserts. The same thing applies to North, Central and, South America; killifish are everywhere except for the desert areas or regions with extreme temperatures.

It is interesting to know that killifish belong to 11 families, and some of these families have a specific geographical location. For example, the killifish that belong to the Aplocheilidae family can be found only on the Indian subcontinent and the African island of Madagascar in the Indian Ocean. 

If you want to locate killifish naturally, you stand the best chance if you check creeks, small streams, and edges of rivers or brooks. The reason is that these locations are the preferred areas of the killifish.

Origin of Killifish

If you are wondering how the name killifish came about or what it even means, the story behind the name is an interesting one. The belief is that it is a derivation from an old Dutch name that was given by European immigrants in the United States in the 17th century to describe small fishes in little water streams. They called them ‘kills’ because the word for little water streams in Dutch is ‘kil’.

Even though this name applied initially to the local fish in the United States, the term is now for all types of killifish seen across the globe, mainly in warm freshwaters. While some of the species of killifish are profusely abundant, some other killifish species are considered endangered. An example of the latter is the Cyprinodondiabolis, limited to just one cave in the United States.

Killifish Physical Features

Because of the staggering number of species of killifish, the specific physical features will depend on the type of species considered. However, one feature that is common to virtually all killifish is that they are tiny in size as they are just a few inches in length. In terms of size, the most prominent killifish species are typically less than six inches. So, what that means is that if you are looking for large fish species, you cannot include the killifish in your search. Virtually all killifish are also bright, attractive, and very graceful – one of the reasons they are favorites of aquarists.

Behavior of Killifish

The good thing with killifish is that when it comes to natural features, a vast majority of their species are peaceful and non-aggressive, thus making handling a lot easier and pleasurable for you. They tend not to cause trouble when placed in community tanks, but you should put it at the back of your mind that the males can be quite violent among themselves.

Because the males can be quite antagonistic to one another, if you are an amateur, it is advisable that you put a pair of killifish in a species only tank. But if you are not an amateur and you desire to put a group of killifish in a bigger container, that is possible once there is enough space and room in the tank.

Another option is that you can have an individual male killifish in each aquarium and also do not keep similar male species together. An extra tip is to put as many females as possible together. That said, killifish are primarily ideal as community fish as they get along pretty well with other non-aggressive fish species.

That said, it must be pointed out at this stage that as you are arranging your tank, you should know that killies can jump with incredible energy. Therefore, you need to ensure that while getting the tank constructed, there has to be an arrangement for a cover that will ensure these smart jumpers do not escape.

Remember that killifish are tiny, and if there are even little spaces in the tank, they can jump through. So, always take note of this fundamental behavior of the killifish species. Some amateurs do not know this only for them to wake up one day to an empty tank.

    Killies are always in the habit of spending most of their time close to the surface of the water. Here, they can observe even the slightest motions, and they react to them. For example, killies jump with a lot of energy, and one of the reasons they do so is that whenever they observe an insect moving, they aim straight for it.

    Even though the killies cannot see the moving insects, they have a set of sensory organs on their heads that helps them in the detection of even the slightest of motions. When an insect or food droplets land on the surface of the water, it creates a ripple of waves that are then detected by the sensory organs of the killifish.

    Feeding of Killifish

    Feeding the killifish is probably one of the most exciting activities about them. A typical meal for a killifish contains crustaceans like prawns, crayfish, krill, and woodlice. Other favorite diet ingredients include insects, worms, and insect larvae. Some killies also consume seaweed and algae.

    In your aquarium, it is best to give killies live meals. This aspect of their nutrition is so vital that if you know that you will not be able to feed them live meals or you think you will start with live meals and continue with something else later on, then honestly you have no business raising killifish.

    When breeding killies, there is a lot of emphases that you need to place on the diversity and balance of their meals. It is vital, and because of this, many knowledgeable aquarium owners choose to prepare meals for their killies. Doing so allows them to meet the precise dietary stipulations of their killies. You can also do the same if you have the right skills, resources, and experience.

    Types of Food

     The widespread belief is that the most nutritious meals for grown killies are:

    •    Daphnia: This is very common and well-accepted and is in many aquariums. You can decide to grown daphnia yourself or get them from natural sources like pools. If you are going for the latter option, then you should be very careful to make sure you are getting only the daphnia, and nothing else. If you choose to feed your killies with these little aquatic crustaceans, you should not forget that they must not be the only food on the diet because they can mess up the digestive system of the killies.

    •    Shrimps: Well-loved by most of the killifish species, brine shrimp is an excellent dietary choice. It is also an excellent option to attempt to feed your killies with cold brine shrimp once in a while. You can also feed them with newly-hatched brine shrimp or even Mysis shrimp. The type of shrimp you are going to use in feeding your killifish will depend on age and weight. You should also know that killies do not like dry meals at all, but some breeders have tried them out and got some remarkable results. Unless you have the relevant skills, resources, and experience, you should not try feeding them with dry food.

    •    Insect Larvae: Because of the growth cycle of the insects, you have to properly time the collection period of the mosquito larvae from the ponds if you choose to get them from natural sources. Another option is for you to decide to breed the insect larvae for yourself. But this should be done if you have the expertise, so you do not end up with a home full of unwanted insects.

        Worms: Killies love worms, but you have to ensure you feed them with the right worms and not just any type of worm. Top on the list of worms used in feeding killies are the black worms, they are considered to be very nutritious, and there are business enterprises that breed them for sale so getting them is not going to be difficult at all.

    There are also the tubifex worms, also considered first-class food options for killifish. But you need to be very careful if you are feeding your killifish with tubifex worms because there is the possibility of infection and this can ruin your precious fish.

    To minimize the risk of infections, place the tubifex worms under running water before feeding the killifish.

    Still, on worms as a food source for killifish, there are white worms, but the only downside to this is that they can contain too much adipose tissue so if you are going to add white worms to the diet of the worms, you have to arrange for substitutes too. There are also some other branded food products like Betta that have been specially prepared to meet the nutritional requirements of the killifish.

    It is best that you do not rely on one source of a meal as the sole option but try and make sure that it is balanced and as nutritious as possible. Give portions that they can finish in a maximum of two minutes; this feeding should be done one or two times in 24 hours.

    But you need to note also that if you are feeding killifish fry, the dietary composition is somewhat different. The best meals for newly-hatched young of killifish are vinegar eels, micro worms, and freshly-hatched brine shrimp. As the fry becomes more mature, then other types of meals can be gradually introduced.

    Breeding of Killifish

    There is one primary reason why killifish are so well-loved by aquarists and fish breeders. Of all the varieties for breeding, killifish consistently rank among the first, and this is because breeding killifish is as stress-free as it can get.

    No one surely wants to run into regular problems while breeding fish, and that is why killifish have emerged as highly-preferred alternatives. For those who wish to produce killifish, one point you must always have at the back of your mind is that there are two kinds of killifish when it comes to the mode of reproduction. The first one is referred to as the non-annual killifish, while the second one is known as the annual killifish.

    Annual Killifish

    As for yearly killifish, they are called thus because, in the water bodies where they are found naturally, they die out every year because the water bodies dry out completely every year. As a result of this, annual killifish have evolved to grow and sexually mature at rapid rates.

    This rate is so fast that it takes just about two weeks. They hide the eggs inside the soil until the water body is back then they hatch.

    So, if you are going to breed annual killifish, you need to have a portable breeding tank with a sandy layer where they can hide their eggs. After the laying of the eggs, you then drain off the water and also remove the killifish.

    The sand layer has to be temperature-controlled and kept wet for about 90 days after which you can then introduce more water, and this usually triggers a new round of hatching. Under ideal circumstances, annual killifish can stay for as long as a couple of years in your aquarium.

    Non-annual Killifish

    Unlike the annual counterpart, non-annual killifish do not live in water bodies that dry out every year. As a result, they can lay their eggs directly in water and do the incubation quickly – also inside the water.

    For non-annual killifish, you do not need to add an extra layer of sand in their tank. In cases where you feel like adding plants inside their breeding tanks, make sure that you take out the parents immediately after egg-laying so that they do not end up consuming the eggs.

    In terms of longevity, non-annual killies do not grow as fast as their annual counterparts.

    Care for Killifish

    Caring for killifish starts from getting the tank requirements entirely right. Even though they are not difficult to breed, there are feeding and tank requirements. These include:

    •    A tank with a capacity of 20 gallons can contain two killifish. In a case where you have more killifish to train, then you have to increase the size of the tank.

    •    The tank should not be deep; it should be shallow to mimic their natural water environments.

    •    Water movement inside the tank should be minimal. The same thing goes for the luminosity; the tank should not be bright at all because as observed in their natural habitat, killifish are not exposed to a lot of sunlight so the same in the tank.

    •    Do not leave the tank bare, include some rocks and soil too. Plants that share characteristics with water lilies are often preferred.

    •    Make sure that the tank is covered because as stated earlier, killifish are very smart and jump with a lot of strength. If the tank is not correctly covered, they will jump out.

    •    Concerning tank temperature, it should be between 72 and 75 degrees Fahrenheit, and you can use a meter to always keep a tab on the heat. As for the pH, it should remain neutral as much as possible, have a pH range of 6.6 and 7.2, and you will be perfectly fine.


    Aquarium fish like killies are very vulnerable to several diseases. This is often because of the unnatural and constrained environments that they are kept. Killifish can suffer from a number of the following diseases:

    Fin Rot Disease: This is often a result of infection by bacteria and the disease chips off the outer margins of the fins. The best way to handle it is to ensure that the water is clean, introduce pharmacological agents to control the infections, and also feed fortified meals to the fish.

    Saprolegnia Fungal Disease: The main manifestations are soft, snowy growths on the fish. The best way to treat is to give food rich in vitamin C and improve the quality of the water.

    Aquarium Mates

    As hinted earlier, killies are good community fish, and are ideal aquarium mates are with other species like Rummy Nose Tetras and Neon Tetras.


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