Killifish: A Complete Guide

Killifish come in a variety of different patterns and colors, and all of them are completely stunning. These freshwater fish make an excellent addition to the aquarium.

No only do they make great tank mates and get along with most fish, they are also pretty easy to care for. In this guide we want to teach you everything you need to know on Killifish to make you a Killifish expert!

We will cover all of the essentials such as how to care for Killifish, diet, aquarium essentials, plus much more.

Killifish Summary

Killifish are colorful freshwater fish and are a member of the Cyprinodontidae family. They are distantly related to swordtails, guppies, platies, and molly fish.

They have stunning patterns and hues, and startlingly bright. Some people can actually be put off by their aggressive sounding name, but they are far from dangerous. Killifish are actually very good natured.

Their name comes from the dutch term killi or killy which refers to the killifish preferred habitat of sleepy streams, low lying channels, or within a ditch.


Killifish Essentials

Killifish Lifespan

The typical lifespan of a Killifish is around 2 to 5 years, providing they have the correct care and a well-kept aquarium with the right conditions.

Appearance & Size

Killifish are very small with an average length of 1 to 2 inches, and some growing a little larger at up to 6 inches.

With over 1200 species of Killifish, here are some of the 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

Males have larger anal and dorsal fins than females, as well as being more noticeable and brighter. A majority of these fish have pike-shaped bodies with a flat top. This shape allows them to swim for long periods of time and long distances.

Depending on the species, some have fins that are long and broad, others are rounded and a bit shorter.

Behavior And Temperament

Although their name sounds very aggressive, Killifish are actually very laid-back and peaceful creatures. This means they make excellent tank mates for other clam tropical fish varieties.

Even though they are calm fish, it’s important to know that male Killies can show aggressive behavior towards each other when inside the same tank.

The easy solution to this is ensure you provide plenty of hideouts for the fish to retreat to. If you are planning to purchase Killifish for the first time, it’s a good idea to just start with one male until you become a bit more experienced with their requirements.

Providing you have a big enough tank, it’s perfectly fine to keep several females together as they are not aggressive.

One final thing to be aware of is their ability to jump high when there is not tank lid present.

Natural Environment

Killifish can be found in in parts of Canada, Argentina, Africa, Southern Europe, and parts of Asia. This species have two different kinds of habitats:

  1. Some live in pools, streams, and swamps in tropical rainforest where the dense forest shades the water from the sun, with temperatures of 68 F to 74 F/20 C to 23 C and low lighting are preferred.
  2. Other Killifish live in ponds on the tropical savannahs.

Killifish Essential Care

It’s recommended by aquarium experts that you have a year or two of fish care behind you before you consider keeping Killifish.

It’s not that they are extremely difficult to care for, but certain issues may arise from time to time and you will need to learn how to handle them. Providing you put in the effort to learn and research, there’s no reason why you cannot get them a little sooner.

One of the main issues and one you should learn about is how to spot diseases such as fluke which this fish is prone too. This happens when a tropical fish becomes infected with gill worms, and then starts to show symptoms of fluke.

More and more mucus is produced by the fish which begins to smother them. Other signs of fluke to look out for are:

  • Hovering near the surface of the water.
  • Swimming upside down.
  • Swimming backwards.
  • Forcefully rubbing gills against objects.
  • Head shacking when in motion.
  • Increase breathing patterns and close off one gill as the disease progresses.

How to treat fluke?

If you catch the disease early enough, fluke can be treated with anti-worm medication.

Killifish Diet

Most Killifish are considered carnivores out in the wild, with a diet of worms, insect larvae, and various crustaceans such as shrimp.

Some other kinds of Killifish are omnivores with a diet made up of algae and various other plant materials. Feeding Killifish live foods rather than flake food is preferred, and something that newbie keepers should consider before purchasing.

It’s also important to feed a balanced, nutritious diet that is similar to what they would eat in their natural habitat. Here are some good recommendations:

  • Mosquito larvae: Obtained from ponds.
  • Brine Shrimp: Packed with nutrients and also available in frozen form for more convenience.
  • Beef Heart
  • Daphnia: Collected from ponds.
  • Worms: Do not feed too much due to high fat content.
  • Fruit Flies
  • Paste Fish Foods
  • Some Specialty Dried Fish Foods

If you plan on breeding Killifish then an even more calculated approach to their diet along with monitoring is required.

Killifish Aquarium Requirements

In this section we will cover all of the information you need to know on Killifish tank requirements.

Tank Setup

  • For a regular pair of Killifish, use a long 20 gallon tank with little to no water movement.
  • For larger species, adjust the tank size accordingly.
  • Make sure to have plenty of live plants, especially floating plants. A great example of this is the cryptocorynes.
  • The bottom of the tank an be bare, but you an also use dark gravel. The gravel should be the type that doesn’t harden the water.
  • If you intend to get bottom spawners then you should use peat instead of gravel. Just make sure it doesn’t contain additives or fertilizers.
  • Make sure to provide plenty of hiding places for you Killifish.
  • Install a good quality sponge filter.
  • Lighting: Low lighting and shade from direct sunlight.
  • Filtration: Use a simple box filter with a filter sponge for a small tank. Use under-gravel filters for larger tanks.
  • Tank Lid: As Killifish are outstanding jumpers, it’s important to ensure you install a sturdy tank lid.

Tank Conditions

Each species of Killifish require different water conditions and can be sensitive when it comes to any kind of changes in the main tank parameters.

In their natural habitats, Killifish live in softer water that is a little acidic. This being said, Killifish bred in captivity are known to become used to any kind of water conditions that they are raised in.

Let’s take a look at some of the general water conditions:

  • Water pH levels: 6.0 to 7.0
  • Water temperature: Mimic sub-tropical water temperatures of 68°F to 75°F. It’s also important to invest in a good aquarium heater.
  • Water hardness: Approximately 7 to 10 degrees or 120 ppm to 160 ppm

Remember that these are just general guidelines. Some Killifish species require different water hardness.

The best thing to do is to simply enquire about what water conditions the Killifish were raised in before you bring them home.

Water Changes

It’s important to make water changes of only 10% when performed weekly to ensure your fish stay healthy and help decrease stress. If water changes are made every two weeks, this should increase up to 20% to 25%.

You should use a water conditioner to treat regular tap water to prevent too much environmental changes that could stress your fish.

You can use an aquarium water changer or a siphon vacuum gravel cleaner for this process.

Good Tank Mates For Killifish?

If Killifish are alone then they can become stressed, which means it’s important to keep them in a group for the sake of their health and well being.

Here are some recommended tank mates for Killifish:

  • Danios
  • Smaller catfish varieties
  • Tetras (neon, green, and ember)
  • Rainbows & other peaceful fish

Keep in mind that 2 or more male Killifish can fight and become aggressive.

Killifish Breeding Tips and Advice

As long as you know the basics, Killifish can be easy to breed. It’s just a case of setting up an environment that mimics their natural habitat.

There are two reproduction characteristics which are “annual” and “non-annual”. Let’s take a look in more detail at both.

Annual Killifish

Killifish out in the wild live in bodies of water that are not permanent, where the water dries up each year. This means that you will need to keep in mind their natural breeding cycle.

These conditions mean that annual Killifish breeding timeline is very short, and will need to reproduce quickly. This process is achieved by laying eggs in moss, where they stay until the water returns.

Here’s how to replicate this process in a tank:

  • Provide plenty of sand or peat moss in the substrate to enable the Killifish to lay their eggs.
  • Once the eggs are laid, remove both the Killifish, and the water from the tank which mimics the process that would happen in the wild.
  • To ensure the eggs an develop, you should keep the substrate warm. It’s also important to ensure that the tank isn’t bone dry. Make sure there is a little moisture.
  • Add water back into the tank after around 90 days so the eggs an hatch.

Non-Annual Killifish

None-annual Killifish are a lot more straight forward to breed than annual. The process is easier because you don’t have to go through the cycle of drying up their home.

The only real thing to be aware of is to make sure there aren’t too many things in the tank such as plants.

The breeding process of non-annual fish is longer and slower than annual, but you can expect them to live longer.

Where to Buy Killifish

You may find it hard to find Killifish for sale at regular pet stores. The best thing to do is to do a search online.

Just make sure you have the correct tank and conditions to match the species before you purchase.


Killifish are colorful and beautiful fish that make an excellent addition to any aquarium. Remember that male Killies can show aggressive behavior towards each, but several females in the same tank are absolutely fine.

If you plan on buying Killifish, make sure to research the species that you plan to get, and ensure you have the correct tank setup to match that species.