Killifish are a very pretty freshwater fish that come in a variety of different colors. The list of different patterns and colors is quite long, and they’re all stunning!

Not only that, but they’re pretty straightforward to care for and get along well with their tank mates.

This makes them a go-to aquarium fish option for many freshwater aquarists.

Since they’re so popular, we wanted to put together this care guide to help new and experienced owners find the essential information they need. By the time you’re done reading this, you’ll be a complete Killifish expert!

Species Summary

The Killifish is a proud member of the Cyprinodontidae family, and these colorful and vibrant freshwater fish are distantly related to guppies, swordtails, platies, and mollies. Unlike those other species, this fish is generally not included in the freshwater aquarium inventory sold at local fish stores.

These interesting fish have stunning color hues and patterns, and most of them can be described as tranquil with an overall good nature.

They are almost startlingly bright and lavishly shaded and can be found in freshwater or sometimes more brackish streams and rivers from parts of Canada all the way down through the Americas into Argentina.

Killifish are also found in parts of Asia, Southern Europe, throughout Africa and even into the Middle East countries. However, these fish are not native to Northern Europe, Antarctica or Australia.

These fish prefer sub-tropical water and somewhat shaded light, but some can survive in other water conditions. Found naturally in still or moving freshwater streams, these fish get the shade they want from overhanging trees or lush overgrowth from lower-lying bushes and other vegetation along the shorelines.

Some potential owners are scared off by its seemingly dangerous name. Fortunately, the Dutch term killi or killy in Killifish refers to the fish’s preferred habitat in low lying channels, sleepy streams or within a ditch.

Killifish Lifespan

With the proper care and right tank conditions, the average Killifish lifespan will typically fall within the 2 to 5 year range when living in a well-kept aquarium.

Left in the wild, this number can be as short as 6 months to a year when living in extreme conditions that dry up the freshwater streams during that region’s dry season (more on this later). If it weren’t for their exceptional ability to adapt over time, this species would not have survived.

Appearance & Size

As far as size goes, Killifish are on the smaller end of the spectrum. The largest of these fish will still rarely hit 6 inches in length, and most only reach a size of 1 to 2 inches.

Killifish swimming

There are well over 1200 species of the Killifish variety. Each one boasts spectacular color shades too exquisite almost to believe.

Here’s a quick list of some of the more common varieties:

  • Clown Killifish
  • Least Killifish
  • Golden Wonder Killifish
  • Gardneri Killifish
  • Blue Gularis Killifish
  • Bluefin Killifish
  • Striped Killifish
  • Mangrove Killifish
  • Gulf Killifish
  • Lampeye Killifish
  • Rainwater Killifish

Like almost every other living creature, the males are much brighter and more noticeable than the females. They also have much larger anal and dorsal fins.

The tops of these fish are rather flat, and the fish’s mouth sits low near the tip and even underneath. Its teeth are generally pointed, curved somewhat and longer in length.

The vast majority of these fish have body shapes that can be described as pike-shaped and somewhat thin. This makes it easy for them to swim long distances for long periods of time. The fins of a Killifish can be rounded and a bit short, and others have fins that are rather broad and long depending on the species.

The Essentials To Killifish Care

Fish experts recommend that individuals get roughly a year or two of experience in fish care before taking on the Killifish.

That said, this fish is not so difficult to care for that a semi-experienced hobbyist can’t give it a try if willing to put in the time, effort and research to learn how to handle common issues that might arise from time to time.

They do have a few special care needs that new owners should have an understanding of before taking them home. A big part of this is learning how to spot diseases that this fish is prone to including fluke.

Fluke symptoms can occur after a tropical fish is infected with gill worms. The fish then begins to produce more mucus, and this can quickly smother them. Owners should pay close attention to the behavior and appearance of their fish to spot this common fish malady.

Killifish typically swim below the water surface to avoid their natural predators. This is because they have a reflective underbelly that helps conceal them from attacks by predators in the water beneath them. Be alert to signs of fluke if your fish begins to hover near the water surface or is swimming upside down.

Also, consider fluke if your Killifish swims backward, begins rubbing their gills against objects forcefully or shakes its head when in motion. As this disease progresses, the fish increase their breathing patterns and often close off one gill.

Fluke can be successfully treated with an anti-worm medication if this fast progressing disease is caught early enough.

Killifish are somewhat sensitive to water changes such as temperature and other main tank parameters. Killifish that live in their native habitats often are used to softer water that is a bit acidic. However, the vast majority of Killifish bred in captivity become used to whatever water conditions that they were raised in.

In general, there are some baseline water parameters you need to look out for.

  • Water pH levels – Aim for somewhere between 6.0 to 7.0. 
  • Water temperature – You’ll want the tank set at a steady 68°F to 75°F that mimics sub-tropical water temperatures (make sure you have a good heater)
  • Tank water hardness  – This should be kept at approximately 7 to 10 degrees or 125 ppm to 160 ppm.

Note: There are some species that need different water hardness than the range listed above. One example of this is the Nothobranchius, which needs very hard water in order to thrive.

These fish require more attention with regards to water/air filtration and optimal temperature settings than most other tropical fish. New fish owners should always install a good quality sponge filter or one that is easily hung at the back of the aquarium.

To stay healthy and decrease stress, the aquarium water should be exchanged at only 10 percent when performed weekly, and up to 20 to 25 percent when completed every other week.

The aquarium water should be kept steady with a good quality aquarium water heater. Most fish experts also recommend that new fish owners use a special siphon vacuum gravel cleaner or an aquarium water changer like those from Aequeon or other brands.

Always treat regular tap water with a reliable water conditioner before filling up your fish tank to keep your fish from experiencing too much stress due to environmental changes during tank water replacement or tank cleaning tasks.

Before bringing your Killifish home, be sure to inquire what water conditions your Killifish were raised in for best end results.

Minimum Tank Size

Since Killifish are rather small, these fish can be kept in smaller desktop variety aquariums. When housing just a trio of these colorful fish, a 5 to 10 gallon tank is usually appropriate

However, use a larger 20 gallon tank for the average community type aquarium setups or when keeping more than a single male inside one tank.

Other Tank Considerations

Other common things experienced Killifish owners put in their aquariums include adding naturally pH lowering peat moss and driftwood. Avoid smaller bottom gravel if planning to have fish able to spawn in your tank.

Instead, utilize softer peat moss that doesn’t contain harmful additives or various fertilizer products, and provide larger rocks and caves for your fish to hang out in to rest when desired.

Keep the tank light somewhat subdued, and this can be achieved with the addition of lower light thriving water plants java ferns or java moss among others such as cryptocorynes. Use mostly floating type water plants, and keep water movement slow and gentle inside the aquarium.

One word of caution when dealing with Killifish is that these lightweight fish species are outstanding jumpers in the wild. Install a sturdy tank lid, and use caution when cleaning or otherwise maintaining your aquarium to keep these frisky fish safely contained.

Ideal Food And Diet

In the wild, a large percentage of Killifish are considered carnivores and eat insect larvae, worms, and various crustaceans like brine shrimp. However, there are certain kinds that would be classified as omnivores and eat mostly algae and other plant materials.

A word of caution from experienced fish breeders is for prospective owners to determine if they will be able to handle feeding these fish live foods rather than simply shaking out fish flake food.

In the aquarium, these fish should be fed a nutritious diet similar to what these fish would normally eat in their native habitats. If planning to breed your Killifish, special attention should be made to providing a balanced diet that has the proper nutrients for good health and breeding success.

Some good examples of recommended diet and food for adults include:

  • Brine Shrimp – Most Killifish do well on this nutrient-packed food choice. Can find frozen too for more convenience
  • Mosquito Larvae obtained from ponds – Follow directions to avoid breeding these pests
  • Daphnia – Live food source also collected from ponds. Add other food as this can have a laxative effect on fish if given too much
  • Various Worms – Use as directed to avoid diseases and too much fat content in the diet
  • Beef Heart
  • Paste Fish Foods
  • Fruit Flies
  • Some Specialty Dry Fish Foods

Many owners make their own fish food to ensure the proper balance of commonly used food ingredients. It is also important to note that they will need closer diet monitoring if you’re planning to breed them.

Additionally, fish owners should be prepared to feed the spawned fry to keep them healthy and strong as they grow.

Behavior And Temperament

For the most part, the majority of Killifish are known to be peaceful with a laid-back kind of temperament. This characteristic makes them ideal tank mates for other calmer tropical fish varieties like neon tetras.

A marked difference to note is that male Killies can be aggressive towards each other when paired inside the same tank. Owners can often handle this by providing their fish with lots of hideouts where the bullied male can hide from their tormentors.

Bluefin Killifish in aquarium

For first-time owners, it’s recommended that they begin with just one male to gain a better understanding of this fish’s care requirements. Females are not aggressive for the most part, and aquariums owners can keep several females together as long as there is enough room in the tank. 

When paired carefully with other similar laid-back fish types, Killifish can make wonderful additions to community aquariums.

A commonly reported behavior is the impressive ability for them to jump high when the tank lid is lifted. This is something you’ll want to look out for since they can take you by surprise.

What Are Good Killifish Tank Mates?

Killifish are naturally school fish when in the wild. This means that they should be kept in a group to ensure their health and well being. When alone, then can easily become stressed. 

It’s also important to remember that 2 or more male Killies can be aggressive towards each other.

Some recommended Killifish tank mates include:

  • Denios
  • Smaller Catfish Varieties
  • Tetras
  • Rainbow & other peaceful fish

Killifish Breeding Advice And Important Distinctions

As long as you provide and maintain an environment that mimics their natural habitat, Killifish can be very easy to breed. You just need to know the basics.

The first and more important distinction you’ll have to make it between the different reproduction characteristics. You see, these fish are either an “annual” or “non-annual” variety.

Let’s take a closer look at what this means.

Annual Killifish

If you have an annual Killifish then you will need to keep their natural breeding cycle in mind. In the wild, these fish reside in bodies of water that aren’t permanent.

At some point every year this body of water dries up which results in all the fish dying (kind of bleak huh).

Because of this, the breeding timeline for annual Killifish is extremely short. The clock is ticking and they need to ensure that they reproduce!

They do this by laying their eggs in moss where it’s safe. The eggs then stay here until the water comes back the following year.

Here’s what this means for breeding annual Killies in your tank:

You should provide them with peat moss or sand in their substrate where they will feel comfortable to bury and lay their eggs. If your fish don’t feel like they have an adequate location for their eggs it can lead to a variety of issues that can stop the process before it starts.

After they have laid their eggs in your tank you’ll want to mimic their environment in the wild by removing the water in the tank. Yes, you should take your Killifish out too (no need to replicate their natural habitat THAT much).

It will now be your job to keep the substrate warm so the eggs can develop. You don’t want your tank to be bone dry though, a little moisture is required.

After around 90 days you’ll add water back into the tank so the fry can hatch.

Breeding Non-Annual Killifish

These fish are much more straightforward to breed. Unlike the annual Killifish, non-annual Killifish don’t have to go through the nightmare of having their home dry up every year.

This means the breeding process is pretty standard. You’ll want to make sure there aren’t too many things in their tank (like plants) so it replicates the areas where they would be laying their eggs in the wild.

Everything about the non-annual fish is longer and slower than their counterparts. Their growth rate is significantly longer, and they can expect to live longer as well.

Wrapping Up

Killifish are one of our favorite fishes here at Aquarium Source. We love the stunning variety of colors and their fun mannerisms.

If you’re thinking about making the leap and getting some, we highly encourage you to do so! You now have the essential knowledge you need to provide good care and ensure that they live happy and healthy lives.

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