Killifish

Killifish key facts

Care level

Intermediate

Lifespan

1-5 years (varies)

Size

3-8cm

Diet

Frozen food, live food, pellets

Tank

20cm cube OK. Pair keeping suited

Water Quality

Varies by species — soft to hard water

Breeding

Annual species have unique dry-egg dormancy

Lifespan

Annuals under 1 year. Non-annuals 3-5 years

Notes

Jumpers — lid essential

About Killifish

Killifish belong to the order Cyprinodontiformes and are found across tropical and subtropical regions of Africa, South America, and Asia, with each region hosting distinct evolutionary lineages. While Japanese medaka (Oryzias latipes) are technically killifish, the term "killifish" in the hobby most often refers to African species such as Nothobranchius and South American genera like Aphyosemion. Males display stunning jewel-toned coloration — turquoise, red, and gold — that has captivated aquarists worldwide for generations. Among the most fascinating are annual species, which have adapted to seasonal pools that dry up each year. These fish complete their entire life cycle before the dry season, leaving behind eggs buried in the substrate that hatch when rains return — a remarkable survival strategy unique in the aquarium hobby. Dried eggs can even be shipped and traded internationally, fostering a vibrant global community. Most killifish are peaceful, though males can be territorial. With over 1,000 species to explore, all suited to modest tank sizes, killifish offer extraordinary depth for any aquarist.

7 things to know before welcoming a Killifish

1. 1Temperature & Water Quality

   Most killifish prefer water temperatures of 22–28°C, and the ideal water hardness varies by species. Research the natural habitat before purchase and match water conditions accordingly. Avoid sudden changes in temperature or water quality, as these can cause stress and disease — change water in small amounts at a time.

2. 2Short-Lived Annual Species

   Some killifish are "annual" species — in the wild, adults die during the dry season and only eggs survive in the substrate. Annual killifish typically live about one year, so collecting and storing eggs becomes a key part of the hobby. Confirm whether the species is annual before purchasing.

3. 3Male Aggression

   Males of most species compete aggressively over territory, so keeping multiple males together requires ample space and hiding spots. For some species, a ratio of one male to multiple females is recommended. Choose tankmates carefully and avoid fish known to nip fins.

4. 4Diet & Feeding

   Killifish thrive on live or frozen foods such as bloodworms and brine shrimp, which enhance coloration and encourage breeding. Prepared dry foods can be used but supplementing with live or frozen foods helps maintain better condition. Feed twice daily in amounts consumed within 3–5 minutes.

5. 5Breeding & Egg Care

   Most killifish deposit eggs in plants or substrate, and moving eggs to a separate container improves hatch rates. Annual species require a unique method — eggs are stored in peat moss under dry conditions and later moistened to trigger hatching. Water temperature and storage duration vary by species, so consult the breeder at the time of purchase.

6. 6Tank Size & Equipment

   Small species can be kept in 30–45 cm tanks, though larger setups help reduce territorial conflicts between males. Many killifish are strong jumpers, so a tight-fitting lid is essential. Hang-on-back filters or sponge filters with gentle flow are well-suited to these fish.

7. 7Availability & Cost

   Common species are readily available at pet stores and aquarium shops, while rarer varieties are often sourced directly from breeders. Prices range from a few hundred yen for common species to over 10,000 yen for rare ones. Factor in initial setup costs — tank, filter, and heater — before making a purchase decision.

Frequently asked questions about Killifish

Q.Are medaka and killifish the same fish?

A.Broadly speaking, both belong to the order Cyprinodontiformes, but in the hobby they are often treated as separate groups. Japanese medaka (Oryzias latipes) and the African or South American killifish have different care requirements, water preferences, and lifespans depending on the species.

Q.How do I store and hatch annual killifish eggs?

A.After collecting eggs, store them in slightly moist peat moss inside a sealed zip bag at 20–25°C in a dark location for the species-appropriate diapause period. Once the rest period is complete, placing the peat in soft water will trigger hatching within hours to days.

Q.Are there beginner-friendly killifish species?

A.Japanese medaka and common African species such as Fundulopanchax gardneri are considered beginner-friendly due to their relative hardiness. Starting with widely available species allows you to build experience before progressing to rarer, more demanding types.

Q.Can I keep multiple killifish species together?

A.Closely related species that look similar may hybridize, so keeping each species in a dedicated tank is the standard practice among serious hobbyists. Size differences can also lead to predation. In spacious, well-planted tanks, some combinations may coexist, but careful monitoring is essential.

Q.What is the typical startup cost for keeping killifish?

A.Basic equipment — a 30 cm tank, filter, light, and heater — typically costs around 10,000–20,000 yen. Fish prices vary from a few hundred to tens of thousands of yen depending on the species. Annual killifish eggs are often an affordable entry point. Ongoing monthly costs generally range from a few hundred to a few thousand yen.

Useful tools for Killifish care

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