The Ultimate Killifish Care Guide: Types, Tank Mates and More…

Are you looking for a colorful fish to brighten up your aquarium?

The Killifish may be what you are looking for.

Killies are a diverse group of more than 1000 species and they come in a wide variety of vibrant colors and shapes.

While they are still fairly rare in the fishkeeping hobby, their popularity is raising because of their peaceful temperament, beginner friendliness and appearance.

However one of the biggest issues with keeping Killies is that they lack of common names. They are usually sold under their scientific name which can be off-putting for beginners.

In this article we explain everything you need to know about Killifish. Keep reading to find out if this vivid fish is right for your aquarium…

Eggers Killifish

Killifish Overview

Killifish

Killifish is the common name used for any fish in the order Cyprinodontiformes (Toothcarps).

These little torpedo shaped fish are well known for their vibrant and diverse colors.

Altogether, Killifish encompass 14 different fish families and over 1000 different species.

They live all over the world (except the Antarctic and Australia) and the majority live in freshwater lakes, rivers, and streams. In fact, it is thought that their common name comes from the Dutch word ‘kill’ which means small stream.

A unique characteristic of these fish is their diversity of reproduction strategies. They can be:

  • Annuals
  • Semi-annuals
  • Non-annuals

Annuals live in temporary bodies of water that dry up for half the year. Therefor annual Killies have evolved to go through their entire life cycle in a matter of months.

Whereas non-annuals live in permanent bodies of water like most other fish.

Annuals live for mere months in the wild but can live a few months longer in an aquarium setting. Whereas semi-annuals and non-annuals can live for around 2-3 years in an aquarium.

Finding killifish can prove to be a difficult task, especially for beginners.

More often than not you will have to use an online retailer – expect to pay around $4.99 for most varieties, however some can cost up to $19.99.

Key Facts:

  • Experience Required: Beginner friendly.
  • Nicknames: Killies.
  • Color Forms: Varies according to the species but males tend to be more colorful.
  • Size: 1-2 inches.
  • Tank Size: Minimum 5+ gallon.
  • Tank Temperature: 68-75°F.
Pros

  • Lots of different vibrant colors available.
  • Very easy to breed in home aquariums.
  • Are very compatible with plants.
  • Well suited to smaller aquariums.
  • Hardy species which can tolerate wide water parameters.
Cons

  • Can be hard to find.
  • Territorial and aggressive to similar looking fish.
  • Some varieties can be expensive.
  • Have a very short lifespan.
  • Tend to only eat live foods which can be expensive.

Killifish Care Guide

Annual Killie

Killies are an easy fish to care for.

They will need a varied diet and stable water parameters. This hardy fish does not require any special care needs in order to live a long and happy life.

Your main task will be to keep their aquarium clean.

If you do not keep their aquarium clean then it can cause them stress which makes them vulnerable to diseases like fin rot and columnaris (a type of bacterial infection that is common in killifish). While simple treatments for these diseases exist, prevention is better than cure.

To prevent the introduction of diseases you should keep track of anything new you introduce in your tank as well as the food you feed your fish.

You cannot overstate how crucial it is to quarantine new plants or fish since they tend to be the main causes for of new diseases.

Diet

In the wild Killifish are predators and prey on small insects, worms and crustaceans.

They have wides mouths for their body size so they can eat foods that other similar sized species can not.

Unfortunately they are not well suited to heavily processed foods like flakes or pellets. Instead they should be fed live and frozen foods.

Just remember that some species have different dietary preferences, so you should keep track of their special requirements. The suggestions listed below are suitable for all Killifish:

  • Water fleas
  • Brine shrimp
  • Cyclops and other copepods
  • Freeze dried micro invertebrates
  • Fruit flies
  • Blood worms
  • Tubifex worms

Killifish thrive on a varied diet so you should avoid feeding them too much of one type of food as this can lead to malnutrition or obesity.

You should also make sure that you feed the correct size meal to your particular species. A Golden Wonder Killifish can eat bigger pieces of food and requires a higher caloric intake when compared to a Clown Killifish.

As for feeding times they have high metabolisms so they should be fed in small meals throughout the day. Annuals should be fed more than non-annuals to support their growth and reproduction. It is best to avoid large single meals to prevent possible complications from feeding.

Behavior

Killifish tend to inhabit the top level of the water column.

They spend a lot of time here as they are constantly searching for insects that have fallen into the water. They also tend to be quite active, especially so during feeding time.

When kept in a school you will see a wide range of schooling activities including swimming and feeding. However not all Killifish will school and some do fine in smaller groups of two or three.

These fish tend not to interact with plants or décor, although they may hide in small places if they feel threatened.

A unique trait is their ability to jump.

This is why it is important to make sure that you get a cover for your tank otherwise you may find your fish outside your tank.

Killies

Habitat and Aquarium Set Up

In the wild killifish habitats can vary quite drastically. Here we will focus on where the majority of species live.

Most Killifish live in swampy, low flow streams or lakes that are shaded by either foliage from above or floating plants. Because of this, these bodies of water tend to be cooler and have low light levels. The water tends to be soft and slightly acidic too due to the vegetation that surrounds their habitat.

A lot of steps must be taken to replicate these water conditions.

Aquarium Conditions

First of all you will need to use soft water without lots of minerals. If soft water is not available then you might have to resort to reverse osmosis water – this is water that is purified of minerals.

Rainwater can also be a valid substitute but you have the risk of contamination. However if you are able to collect it safely then feel free to use it if you feel comfortable.

To maintain soft water and low acidity you can also introduce a peat moss filter or driftwood to your tank.

Peat moss can be placed in the filter or as a substrate layer and it will absorbs minerals through a process called chelation. The same process occurs for driftwood.

The combination of low light levels and vegetation can prove to be a difficult combination. However there are plants that excel in these conditions such as Java Fern, Duckweed, and Hornwort.

Duckweed especially is useful because it can create shade in the aquarium too.

You will need to match the water conditions outlined in the table below.

Tank Parameter Requirement
Minimum Tank Size 5 Gallons
Tank Type Planted freshwater
Temperature 68-75°F
pH 6.0-7.0
Hardness 4-15 dGH
Flow Low
Substrate Peat moss or sandy

What Size Aquarium Do They Need?

A 20 gallon tank is more than big enough to keep any type of Killifish. This tank is suitable for schooling as you can fit around 8-12 individuals.

All of the 5 species we mentioned earlier would comfortably fit in a 5 gallon aquarium. A small 5 gallon tank is suitable for a group of 3 small killifish.

Killifish Appearance

Killi

While there are over 1000 recorded species of Killifish they all share some common characteristics.

They are small and slender fish that usually range from 1-2 inches long – although some species reach longer lengths.

Killies have evolved to hunt small prey and insects on the water’s surface. Because of this they have developed certain adaptations to help. Their most recognizable trait is their wide mouths that let them eat larger prey. They also have rounded caudal fins and fins centered at the end of their posterior which lets them burst quickly and navigate tight corners.

You can find this small fish in pretty much any color and they are usually bright with remarkable patterns.

This fish is also sexually dimorphic with the males having larger fins and more vivid colors.

Common Color Varieties

Here are descriptions of the 5 most popular beginner Killifish.

Clown Killifish (Epiplatys annulatus): These are non-annual killifish that have an easily recognizable appearance. They have black and yellow stripes with a tail pattern and color that looks like a rocket booster. You can expect them to grow to 1.2-1.4 inches and they thrive in larger numbers.

Lyretail Killifish (Aphyosemion australe): This vibrant non-annual killifish is easily identified by their tail that looks like a lyre. Lyretails are bright orange with dark black spots and lines on their fins. They average around 2 inches and it is not uncommon for them to reach 3 years old.

Golden Wonder Killifish (Aplocheilus lineatus): These Killies are much more affordable and come in a wonderful golden color. They are non-annual and reach 2-2.5 inches in size.

Red Striped Killifish (Aphyosemion striatum): This species is well known for their red stripes against their blue body. They are well suited for beginners and will live for around 2 years.

Neon Stripe Lampeye Killifish (Aplocheilichthys macrophthalmus): Despite their long name, this fish is actually one of the smallest species of Killifish. Their name comes from their horizontal crescent shape above their eyes that appear to glow in aquariums.

These 5 species only scratch the surface of what this family has to offer. Due to the sheer number of species there is no way to name them all.

History and First Sighting

The name Killi comes from an old Dutch name and this was used by immigrants to the Americas in the 17th century to describe the small fish that they see living in these streams.

Killifish apparently reminded them of their home country.

From here the term progressively branched out to related fish from other countries and then to aquarists of the 19th century who took an interest in these fish.

It was during this time that Killifish were caught and first bred for fish keeping.

Their popularity continued and now there are 1000s of recognized wild species with dozens that are popular with aquarists.

Clown Killifish

Best Tank Mates For Killifish

Killifish live across a diverse geographic region.

This means that any other fish that live in these conditions could be considered as a tank mate.

They do best with other peaceful species and bottom dwelling fish in particular work well because Killifish stay in the top half of the water column. Some examples of bottom dwelling fish include Corydoras and Kuhli Loaches.

Other good tank mates include: Tetras, Rasboras, and live bearers of a similar size. Even larger species like Dwarf Gouramis can work as they do not grow too much bigger than Killifish.

You should avoid any species which look similar to the male version of the Killifish. Also make sure to avoid larger more aggressive fish like Angelfish and Barbs. These larger fish should be avoided as they will only stress out your fish.

Smaller fish (like fry) should be avoided too since they will be considered prey.

Invertebrates too like Shrimp and Snails will be an expensive, yet tasty snack for killifish. Also the soft water condition will eat away at their calcium carbonate shells.

Just remember that any tank mate should be able to live in low light, soft acidic waters. Also make sure that when feeding your fish, the tank mates do not outcompete each other for food.

Keeping Killies Together

Killifish thrive when they are kept together.

You should keep at least 3 of them together (1 male and 2 females).

In larger tanks (30+ gallon tanks) you can keep up to 12 individuals and they will school together. Also in these larger tanks you can keep multiple males together as they hare the space and opportunity to hide if needed.

A Clown Killifish

Breeding Killifish

Breeding for killifish depends on if your particular species is non-annual or annual.

Generally annual Killifish are easier to breed at home although it is a labor intensive process.

This particular section will focus on species of killifish that lay eggs. Live-bearing easily breed and do not require as intensive requirements.

First you need to research the specific needs of your species. Some may need a layer of peat moss to lay their eggs on, while others need plant foliage or a spawning mop to lay their eggs. Regardless of the substrate, you need to make sure your tank is properly setup.

Now you will need to set up potential mating pairs with each other.

Start with a single male and multiple females. The male will court the females and eventually he will establish a mating pair. Once a mating pair is established you should check your substrate daily for any eggs.

Because Killifish do not look after their young they can sometimes eat their eggs or hatchlings.

Therefore you should remove the eggs from the tank as soon as you notice them.

Using a spawning mop or peat moss you can remove the eggs from the tank and any excess water should be removed. The eggs need to be taken out of the water and placed in a moist environment otherwise they will not hatch.

Killifish eggs take generally around 3 months to hatch.

Once the eggs hatch you can add water back to the tank. From here, the fry should be fed small prey such as infusoria. These fry will mature and grow very quickly due to their short life span.

Species Summary Table

Killifish
Other Common Names: Killies, Toothcarps and Livebearers
Scientific Name: Cyprinodontoidei
Family Name: Includes 14 different family names, including: Nothobranchiidae, Cyprinodontidae and Rivulidae.
Distribution: Worldwide
Size: 1-13 inches
Color: Polka dot red most popular
Care Level: Easy/Moderate
Temperament: Peaceful
Lifespan: 2-3 years
Minimum Tank Size: 5 gallons
Tank Mate Compatibility: Compatible with similarly sized species

Should You Keep Killifish? (Summary)

Killifish are relatively obscure in the fishkeeping hobby and this is a shame because they are some of the most stunning fish around.

They are a great choice for fish keepers of any experience level.

Their rarity too is also a nice conversation starter for those who feel there is an overabundance of more common fish like Bettas and Neon Tetras.

After reading this article you should now be more familiar with the intricacies of caring for Killies.

They are always a standout species and this choice will be something that you will not regret.

Let us know in the comments section below if you have kept Killifish before…

David Thomas Author Bio Picture
David Thomas leads the team at Everything Fishkeeping as the Editor-in-Chief. David has been keeping fish since he was a child. In his first tank he kept goldfish and since then he has kept over 30 different species. Now he has 4 separate tanks and his favorite is a 100 gallon freshwater tank with a school of Rasboras, Tetras and Loaches.

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