Killifish

Male Killifish Golden Wonder Panchax (Aplocheilus lineatus) | Pavaphon Supanantananont

Killifish are some of the most colorful and fascinating freshwater fish available to aquarists. From tiny clown killifish with flame-like tails to brilliant blue, red, orange, and yellow African species, the group includes an enormous variety of fish with very different appearances, behaviors, and breeding strategies.

The name killifish does not refer to a single species. Instead, it is commonly used for numerous egg-laying fishes within the order Cyprinodontiformes. Their natural habitats range from forest streams and permanent ponds to temporary pools that disappear completely during dry seasons.

This diversity means there is no single set of water parameters that works for every killifish. Some species are excellent choices for beginners, while others are best left to experienced breeders.

What most aquarium killifish have in common is brilliant coloration, fascinating reproductive behavior—and an impressive ability to jump.

🐠 Killifish Care at a Glance

Care Requirement	Killifish
Scientific classification	Multiple genera and species
Common aquarium genera	Aphyosemion, Fundulopanchax, Epiplatys, Nothobranchius, Aplocheilus
Origin	Africa, Asia, the Americas, and other regions depending on species
Adult size	Commonly about 1–4 inches; some species grow larger
Lifespan	Often 2–5 years for non-annual species; some annual species are much shorter-lived
Minimum tank size	Often 5–20+ gallons depending on species
Temperature	Commonly around 68–78°F, but species requirements vary
pH	Highly species-dependent
Temperament	Peaceful to semi-aggressive depending on species
Diet	Primarily carnivorous or omnivorous
Swimming level	Many favor the upper and middle levels
Care level	Beginner to advanced depending on species

The American Killifish Association emphasizes that killifish requirements vary substantially among species, although all need the same fundamentals as other aquarium fish: clean water, appropriate food, enough space, and a secure covered aquarium.

🎨 What Do Killifish Look Like?

Killifish are famous for their coloration.

Males of many species display combinations of:

Electric blue
Turquoise
Red
Orange
Yellow
Green
Black
Metallic gold

Their bodies may be decorated with stripes, spots, bars, or intricate mosaics of contrasting colors.

Females are often more subdued, usually appearing tan, gray, silver, or brown. This sexual dimorphism makes many adult killifish relatively easy to sex.

Body shape also varies. Some are slender surface-dwellers, while others have deeper, more robust bodies.

The orange australe killifish (Aphyosemion australe), for example, reaches about 6 centimeters in total length and is available in both chocolate and gold aquarium forms.

🌍 Where Do Killifish Come From?

Killifish occur across several continents.

Many of the species prized by aquarium keepers come from Africa, especially tropical regions of West and Central Africa.

Others originate in:

South America
Central America
North America
India
Southeast Asia

Their habitats are just as diverse.

Depending on species, wild killifish may inhabit:

Forest streams
Swamps
Marshes
Shallow ponds
Floodplains
Temporary rain pools
Slow-moving creeks

For example, the popular Gardneri killifish (Fundulopanchax gardneri) occurs in brooks, swamps, pools, and streams in forested regions of western Africa.

✨ Popular Killifish Species

There are hundreds of killifish species, but a handful are especially common in the aquarium hobby.

Popular choices include:

Gardneri Killifish (Fundulopanchax gardneri)
Orange Australe Killifish (Aphyosemion australe)
Clown Killifish (Epiplatys annulatus)
Golden Wonder Killifish (Aplocheilus lineatus)
Blue Gularis (Fundulopanchax sjoestedti)
Various Nothobranchius species
Red-Striped Killifish (Aphyosemion striatum)

Aquarium Co-Op recommends several of these as approachable choices for aquarists interested in trying killifish, including clown killifish, Gardneri killifish, australe killifish, and Golden Wonders.

🧬 Annual vs. Non-Annual Killifish

One of the most fascinating aspects of killifish biology is the distinction between annual and non-annual species.

Annual Killifish

Annual killifish naturally inhabit temporary bodies of water that dry up during part of the year.

Adult fish may not survive the dry season. Instead, their eggs remain buried in the substrate and enter periods of delayed development known as diapause.

When rains return and refill the pools, the eggs hatch.

The young then grow rapidly, mature, reproduce, and deposit another generation of eggs before the habitat disappears again.

Many Nothobranchius species are annual killifish.

Non-Annual Killifish

Non-annual species inhabit more permanent bodies of water.

Their eggs do not generally require the prolonged dry incubation associated with true annual species.

Popular aquarium fish such as Fundulopanchax gardneri and Aphyosemion australe are non-annual species. FishBase specifically describes both species as non-seasonal killifish.

The American Killifish Association provides detailed breeding guidance for both annual and non-annual species because their egg-incubation requirements can be dramatically different.

🏡 Killifish Tank Size

Tank size depends heavily on the species.

Many small killifish can live comfortably in aquariums between 5 and 20 gallons, while larger or more active species need considerably more room.

A 10-gallon aquarium can work well for a pair or trio of several smaller species, especially when the tank is heavily planted.

A larger aquarium offers:

More stable water quality
Extra swimming room
More hiding places
Greater flexibility with tank mates
Better opportunities for maintaining groups
Reduced territorial pressure

Aquarium Co-Op lists species such as Gardneri, australe, and red-striped killifish as possible choices for properly arranged 10-gallon species aquariums.

🚪 Killifish Need a Tight-Fitting Lid

This might be the single most important piece of practical killifish advice:

Cover the aquarium.

Killifish are notorious jumpers.

Many naturally feed near the water’s surface and can leap through surprisingly small openings.

Check gaps around:

Filter pipes
Heater cables
Airline tubing
Feeding openings
Aquarium corners

Even a tiny opening may be large enough for a determined killifish.

The American Killifish Association specifically warns that many killifish are accomplished jumpers and recommends securely covering their containers.

🌡️ Killifish Water Temperature

Many commonly kept killifish prefer somewhat cooler water than typical tropical community fish.

Temperatures around 68–78°F work for many popular species.

Some can tolerate warmer water, while others perform best toward the cooler end of that range.

Clown killifish, for example, are commonly maintained in the low-to-mid 70s, while Golden Wonder killifish are comfortable around 72–78°F.

Do not assume every killifish needs identical temperatures.

Research the exact species before setting up the aquarium.

Colorful Killifish in planted aquarium | Selosh

💧 Killifish pH and Water Hardness

Water chemistry varies tremendously among killifish.

Many African forest species prefer:

Soft water
Slightly acidic conditions
Low to moderate mineral content

Others are considerably more adaptable.

For example, FishBase lists Fundulopanchax gardneri at approximately:

pH: 6.0–7.2
Hardness: 5–8 dH

Meanwhile, Aphyosemion australe is listed at approximately:

pH: 6.0–7.0
Hardness: 5–12 dH

Rather than using a generic “killifish pH,” find the requirements of the species you intend to keep.

Stable water is also preferable to constantly adjusting pH with chemicals.

🧹 Water Quality and Maintenance

Killifish need clean, stable water just like any other aquarium fish.

Maintain:

Ammonia: 0 ppm
Nitrite: 0 ppm
Nitrate: Controlled through regular maintenance

Perform routine partial water changes and avoid allowing uneaten food or organic waste to accumulate.

Many killifish aquariums are relatively small, which makes maintenance particularly important. Water conditions can deteriorate faster in a 5- or 10-gallon tank than in a large aquarium.

If you’re new to cycling aquariums, see How to Set Up Your First Aquarium: A Beginner’s Guide.

🔄 Filtration for Killifish

Most killifish do not require powerful currents.

Gentle filtration is often preferable, especially in breeding tanks.

Good options include:

Sponge filters
Small hang-on-back filters
Internal filters
Air-driven filtration

Sponge filters are particularly useful because they provide biological filtration without creating strong flow or sucking tiny fry into the filter.

They also develop microorganisms that young fish may graze upon.

🌿 How to Set Up a Killifish Aquarium

A planted aquarium works beautifully for many killifish.

Useful plants include:

Java moss
Java fern
Anubias
Water sprite
Hornwort
Guppy grass
Floating plants

Plants provide shelter, spawning sites, visual barriers, and hiding places for fry.

The American Killifish Association notes that planted aquariums can provide egg-laying sites, cover for fry, microscopic foods, and additional assistance with water quality.

You can find more suitable plants in Top 30 Easy-to-Grow Live Aquarium Plants for Freshwater Tanks.

🍂 Do Killifish Like Tannins?

Many forest-dwelling killifish naturally occur in water containing leaf litter and decomposing botanical material.

Aquarists sometimes recreate these conditions using:

Indian almond leaves
Alder cones
Driftwood
Other aquarium-safe botanicals

These materials can release tannins and create amber-colored water reminiscent of some natural habitats.

However, not every killifish requires a blackwater aquarium.

Again, match the setup to the species.

🍽️ What Do Killifish Eat?

Many killifish are strongly oriented toward animal-based foods.

In nature, their diets may include:

Insect larvae
Small crustaceans
Worms
Aquatic insects
Zooplankton
Other small invertebrates

FishBase reports that Aphyosemion australe, for example, feeds on worms, crustaceans, and insects.

In the aquarium, suitable foods can include:

High-quality flakes
Micro pellets
Frozen bloodworms
Brine shrimp
Daphnia
Frozen cyclops
Live blackworms
Mosquito larvae where safe and legal
Baby brine shrimp

Some species readily accept prepared foods, while others show a strong preference for frozen or live foods.

Offering variety usually produces the best coloration and breeding condition.

🦐 Do Killifish Eat Shrimp?

Some do.

Tiny killifish such as clown killifish may coexist with adult shrimp under appropriate conditions, but larger species can easily view dwarf shrimp as food.

Golden Wonder killifish are particularly capable predators and should not be trusted with very small fish or shrimp that fit into their mouths.

Shrimp fry are potentially vulnerable to virtually any fish.

If breeding shrimp is your goal, a shrimp-only tank remains the safest choice.

🤝 Killifish Tank Mates

Whether killifish belong in a community tank depends on the species.

Smaller peaceful species can sometimes live with compatible fish such as:

Small rasboras
Small tetras
Corydoras
Peaceful dwarf fish
Small peaceful loaches

Clown killifish can work especially well with tiny community species because they remain under about 1.5 inches long.

Larger killifish require more caution.

A fish such as the Golden Wonder may eat small tank mates even though it is not an especially large aquarium fish.

🚫 Killifish Tank Mates to Avoid

Depending on the killifish species, avoid:

Very aggressive cichlids
Persistent fin-nippers
Much larger predatory fish
Extremely boisterous feeders
Tiny fish that could be swallowed
Species requiring incompatible temperatures or water chemistry

Killifish compatibility cannot be generalized.

A clown killifish and a Golden Wonder killifish are both “killifish,” but their appropriate tank mates can be completely different.

Explore additional freshwater species in The Top 50 Freshwater Fish for Aquariums.

🐟 Killifish Behavior and Temperament

Many killifish are peaceful toward other species but can become territorial with their own kind.

Males may display toward one another by:

Spreading their fins
Intensifying their colors
Chasing rivals
Defending small territories

Providing dense plants and visual barriers helps subordinate fish escape persistent attention.

In species where males constantly pursue females, keeping a trio of one male with two females can sometimes reduce pressure on a single female.

Species-specific research is essential, however, because social behavior varies widely.

🌊 Where Do Killifish Swim in the Tank?

Many popular killifish spend much of their time near the upper portion of the aquarium.

This makes them excellent fish for aquariums where the middle and bottom levels are already occupied.

Clown killifish and Golden Wonders are particularly strong surface-dwellers.

Floating plants can help them feel secure while still leaving open patches for feeding.

Their preference for the surface also helps explain why secure aquarium lids are so important.

Steel Blue Killifish – Fundulopanchax gardneri | boban nz

🥚 Breeding Killifish

Breeding is one of the biggest attractions of keeping killifish.

Different species use dramatically different reproductive strategies.

Two broad methods are commonly encountered.

Plant and Mop Spawners

Many non-annual killifish deposit eggs among:

Fine-leaved plants
Java moss
Floating plant roots
Synthetic spawning mops

Aquarists can remove the eggs and incubate them separately or allow breeding to occur naturally in a heavily planted aquarium.

The American Killifish Association notes that some plant-spawning species can reproduce almost continuously in densely planted tanks, with fry occasionally appearing without intensive intervention.

Substrate Spawners

Many annual killifish deposit their eggs into soft substrate.

Aquarists commonly provide an appropriate spawning medium, collect it, and incubate the eggs outside the aquarium for a species-specific period.

The substrate is later rewetted to trigger hatching.

Annual killifish breeding can therefore become a fascinating project for aquarists interested in unusual reproductive biology.

⏳ Killifish Egg Incubation

Incubation time depends enormously on species and breeding strategy.

The American Killifish Association notes that many non-annual eggs may hatch after roughly two to three weeks under typical conditions, while eggs from some annual species can require incubation periods lasting several months.

This is one area where generic killifish advice can cause problems.

Always research the specific:

Species
Collection location or strain
Spawning method
Incubation medium
Incubation temperature

before attempting to hatch eggs.

👶 Caring for Killifish Fry

Newly hatched fry can be extremely small.

Depending on species and fry size, first foods may include:

Infusoria
Microworms
Vinegar eels
Newly hatched brine shrimp
Powdered fry food
Other microscopic live foods

As the fry grow, they can transition to larger foods.

Young killifish often benefit from frequent small meals, but heavy feeding requires equally careful attention to water quality.

A mature sponge filter and live plants can help provide both filtration and microscopic organisms for young fry.

📦 Buying Killifish Eggs

Unlike most aquarium fish, killifish are sometimes sold as eggs rather than live adults.

This is particularly common with annual species whose eggs naturally survive extended periods outside standing water.

Aquarists can obtain eggs, incubate them according to species-specific instructions, and hatch their own fish.

This can be an exciting way to enter killifish keeping, but it is not necessarily the easiest option for beginners.

If this is your first killifish aquarium, starting with healthy captive-bred juveniles or adults of a forgiving non-annual species may be simpler.

🩺 Common Killifish Health Problems

Killifish can be quite hardy when their needs are met.

Warning signs of trouble include:

Clamped fins
Loss of appetite
Faded coloration
Rapid breathing
White spots
Flashing
Lethargy
Weight loss
Unusual swimming
Skin lesions

Before treating a fish, check:

Ammonia
Nitrite
Nitrate
Temperature
pH
Filter operation

Also consider whether any new fish, plants, or equipment were recently added.

Quarantining new fish before introducing them to an established aquarium is one of the best ways to reduce disease risk.

⏱️ How Long Do Killifish Live?

Lifespan varies dramatically.

Many non-annual aquarium killifish can live approximately 2–5 years, depending on species and care. Aquarium Co-Op notes this general range for several commonly kept varieties.

Annual killifish can have much shorter natural lives because they evolved in habitats that disappear seasonally.

Their eggs—not the adults—are adapted to survive the dry period.

This unusual life cycle is one reason annual killifish have become so important to scientists studying aging and developmental biology.

🌟 Are Killifish Good for Beginners?

Some are.

Beginner-friendly choices include species such as:

Gardneri Killifish
Clown Killifish
Golden Wonder Killifish
Australe Killifish

Even these fish require research because their tank size, diet, temperament, and water requirements differ.

The American Killifish Association points out that while certain species can be challenging, many others are no more difficult to maintain than common tropical aquarium fish.

The most important rules for a first killifish aquarium are simple:

Choose the species before setting up the tank.
Research its exact water requirements.
Use a secure lid.
Provide plenty of cover.
Feed a varied diet.
Maintain excellent water quality.

❤️ Are Killifish Worth Keeping?

Absolutely.

Killifish offer something unusually special in the freshwater hobby. Their colors can rival marine fish, their breeding strategies are among the most fascinating found in aquariums, and many species can thrive in relatively modest-sized tanks.

They also reward aquarists who enjoy learning about individual species rather than applying one universal care formula.

A planted aquarium containing a brilliant pair of Gardneri killifish, a group of tiny clown killifish, or an annual species whose eggs have just emerged from months of incubation can offer an entirely different experience from the typical community tank.

Just remember the golden rule of keeping killifish:

Know which species you have—and keep the lid closed.