What Fish Can Live with Killifish? Compatibility and Setup

Three criteria must overlap for any companion to thrive alongside killifish: matching water chemistry, matching size and temperament, and respect for the fish’s preference for calm, planted surroundings. Small tetras, rasboras, corydoras catfish, otocinclus, and kuhli loaches are the most reliable choices for a killifish community tank. Aggressive fish, fin-nippers, and hard-water species create problems within a few weeks of introduction.

The guide below covers which species pair with which killifish, what water parameters to match, and how to set up the tank so every fish thrives long-term.

Understanding Killifish Temperament Before Choosing Tank Mates

Most killifish in the hobby belong to genera like Aphyosemion, Fundulopanchax, and Epiplatys, and their behavior varies more than their bright colors suggest. Aphyosemion australe (the lyretail killifish) is a peaceful surface-dweller that groups well, while a male Fundulopanchax gardneri can claim a 20-gallon tank during breeding windows.

Long, flowing fins on species like Fundulopanchax, Aphyosemion, and Epiplatys annulatus make them targets for fin-nipping fish, even when the nippers aren’t usually aggressive. The same fins that catch your eye in a store tank shred overnight in the wrong company.

Breeding Behavior Changes the Equation

Even peaceful killifish turn defensive around a spawning mop or dense plant cluster. A male guarding a territory will flare, chase, and sometimes nip tank mates that wander too close. Removing the mop or thinning the plants calms the tank within days.

Annual killifish, particularly Nothobranchius furzeri, add a different wrinkle: their entire breeding cycle runs on a compressed timeline, and they often do best in species-only setups where that biological pressure isn’t competing with community dynamics.

Water Parameters That Determine Compatibility

Soft, slightly acidic water suits most commonly kept killifish and their ideal tank mates. pH between 6.0 and 7.0, hardness below 10 dGH, and temperatures in the 72–78°F range create a window where tetras, rasboras, corydoras, and killifish all overlap comfortably.

“Peat filtration or Indian almond leaves push pH down and tint the water amber, replicating the soft blackwater conditions most killifish evolved in. This small change often turns a stressed killifish into a confident one within a week.

Species That Share Killifish Water Conditions

Tank Mate Group	Preferred pH	Preferred Hardness	Compatibility Note
Small tetras (ember, neon, lemon)	6.0–7.2	2–8 dGH	Excellent overlap
Rasboras (harlequin, chili, lambchop)	6.0–7.0	2–8 dGH	Excellent overlap
Corydoras catfish	6.0–7.5	2–12 dGH	Good overlap
Otocinclus	6.0–7.5	2–12 dGH	Good overlap
Livebearers (guppies, platies)	7.0–8.2	10–25 dGH	Poor overlap
African cichlids	7.8–8.6	15–25 dGH	Poor overlap

Hard-water species like livebearers and most African cichlids struggle in the low-mineral conditions killifish need. Forcing both groups into the same water leaves one (usually the livebearer) chronically stressed and the other (usually the killifish) gasping near the surface.

Because those mismatched parameters quietly undermine every pairing, it helps to know which mid-water species can actually tolerate the same conditions.

Peaceful Mid-Water Fish That Pair Well With Killifish

Small, calm schooling fish fill the mid-water column without competing with killifish for food or territory. The right tetras and rasboras stay out of the killifish’s spawning zones and stay small enough that the killifish never sees them as prey or threat.

Tetras and Rasboras as Ideal Companions

• ▸Ember tetras: Their tiny size and warm orange tone complement killifish colors without triggering any predatory response.
• ▸Neon tetras: A school of six or more adds movement at mid-depth and never bothers a killifish’s fins.
• ▸Lemon tetras: Slightly larger but still peaceful, and they tolerate the same soft, acidic water.
• ▸Harlequin rasboras: Hardy, calm, and shaped differently enough from tetras to add visual variety.
• ▸Chili rasboras: Stay under an inch and add bright red color without crowding the killifish’s space.
• ▸Lambchop rasboras: School tightly and stay near the middle of the tank, leaving the surface for killifish.

When Gouramis Work and When They Don’t

Dwarf gouramis and honey gouramis can share space with calmer killifish like Aphyosemion in tanks of 20 gallons or more. The risk comes from a curious gourami investigating a killifish’s spawning mop, which the killifish interprets as a territorial challenge. A heavily planted layout with visual barriers usually prevents escalation.

Boisterous swimmers like danios and tiger barbs stress killifish by outcompeting them at feeding time and darting through their territories. Even “peaceful” danios are too fast and too active for a killifish that prefers hovering near plants.

Bottom-Dwellers and Algae Eaters That Reduce Competition

Bottom-dwelling fish stay out of the killifish’s way entirely, which is exactly what you want. They clean leftover food, graze algae, and add activity at the substrate level without ever entering the killifish’s preferred swimming zone.

Best Bottom-Dwellers for a Killifish Tank

• ▸Corydoras catfish: A school of six or more stays busy along the substrate and never crosses into the killifish’s territory.
• ▸Corydoras pygmaeus: This dwarf species works especially well in 10–15 gallon setups and stays under an inch.
• ▸Otocinclus: A group of three to five handles algae without disturbing the killifish or competing for swimming space.
• ▸Kuhli loaches: Nocturnal and hidden most of the day, so they add life at the bottom without creating conflict.

Larger plecos and Chinese algae eaters pose a real risk to slow-moving killifish. A common pleco grows past 12 inches and may latch onto a killifish’s side to feed on slime coat. Chinese algae eaters become aggressive with age, especially in tanks without enough algae to graze.

Fish and Setups to Avoid With Killifish

Some combinations look reasonable on paper and fall apart within days. The categories below cover the most common pairing mistakes that lead to injured or dead fish.

Fin-Nippers and Aggressive Species

Tiger barbs, serpae tetras, and rosy barbs treat killifish fins as invitations. Even a single nip-stress event can lead to infection, fin rot, and a downward spiral that’s hard to reverse. Aggressive cichlids, even dwarf varieties like Mikrogeophagus ramirezi (German blue ram), push killifish around at feeding time and during territory disputes.

Tiny Fish and Predation Risk

Any fish under one inch risks being eaten by a medium or large killifish, especially Fundulopanchax species that grow past three inches. Chili rasboras, baby guppies, and freshly hatched fry are all on the menu for an adult Fundulopanchax gardneri.

Species-Only Situations

Annual killifish like Nothobranchius species often need their own dedicated setup. Their short lifespan, specific breeding requirements, and sensitivity to disturbance make community tanks stressful for them and for whatever lives with them. A 10-gallon species-only tank with a spawning mop and peat substrate is a better long-term home.

“Carinotetraodon travancoricus (the Indian dwarf puffer) is sometimes suggested as a nano tank mate, but its fin-nipping behavior and brackish-water preferences make it a poor match for any killifish. Skip this combination entirely.

Tank Size, Layout, and Long-Term Cohabitation

A 10-gallon tank houses a killifish pair with a small group of ember tetras or chili rasboras comfortably. Once you add corydoras, otocinclus, or multiple killifish species, moving to 20 gallons prevents the crowding that triggers territorial behavior.

Layout Choices That Reduce Conflict

Dense planting, driftwood arches, and floating plants break sightlines so a killifish can’t see a potential rival across the tank. Java fern, Anubias, and water sprite grow easily in soft, acidic water and provide the structure killifish need to feel secure. Floating plants like frogbit or red root floaters dim the light from above, mimicking the shaded habitats most killifish evolved in.

Feeding Strategies for Mixed Communities

Killifish eat slowly and methodically, which puts them at a disadvantage next to faster schooling tetras. Target feeding with a turkey baster or pipette near the killifish’s favorite spot ensures it gets enough food. Sinking pellets for the corydoras keep them occupied at the bottom while the killifish feeds at the surface or mid-water.

• ▸Surface feeding: Small frozen foods like daphnia and bloodworms sink slowly, giving killifish time to find them.
• ▸Mid-water feeding: Micro-pellets sized for tetras work for killifish too, and prevent faster fish from stealing everything.
• ▸Bottom feeding: Sinking wafers or pellets keep corydoras and otocinclus occupied away from the killifish’s feeding zone.

Watch the tank closely during feeding for the first two weeks, and adjust portions if the killifish looks thin or the tetras look overfed.

Bottom Line

Killifish do best in calm, planted community tanks with small, peaceful species that share their preference for soft, slightly acidic water. Match chemistry first, temperament second, and size third, and you’ll avoid most of the pairing mistakes that trip up new keepers. When in doubt, set up a species-only tank: a killifish with no tank mates and perfect water is healthier than one stuck with the wrong roommates.

FAQ