The Killifish are very diverse and extraordinary fish, highly favored by dedicated aquarists!
Killifish are intriguing and quite beautiful. They come from many diverse habitats and range from hardy to extremely difficult to keep. Killifish live in both moving and still waters. Mostly they are freshwater fish, however there are a few species that are brackish and some even saltwater. Many species can be demanding and have quite specific needs. As each type will have its own set of requirements they are often kept in species tanks.
The order of Cyprinodontiformes, commonly known as Killifish, has over 1250 species that are currently classified into 10 families. This is a very widespread and diverse group of fish, primarily Killifish or Tooth Carps including the Lampeye, Medaka, and Panchax species, but also including species of Pupfish and Topminnow. They are found in tropical and subtropical regions on all continents except Australia. They are also absent from Antarctica and northern Europe. Killifish inhabit and have adapted to a wide variety of environments.
An intriguing fact about Killifish, some species have a life span that only lasts as long as the mud puddle they live in. One species that basically lives in mud puddles, will hatch and then mature in just 3 weeks. They will then lay their eggs and push them into the mud just in time for the mud puddle to dry up and eliminate the parents. But when the rains come and refill the mud puddle, the eggs hatch and the cycle starts all over again!
In general most of these fish are best kept by very dedicated aquarists who are prepared to research the individual species and provide them with top quality water conditions and top quality food. When their needs are met many can readily be kept in captivity with a lifespan of 5 years or more, and most will spawn in the aquarium. For information on breeding Killifish, see Breeding Freshwater Fish: Killifish
The Killifish species list below includes popular types, as well lesser known Killifish varieties. Each fish guide has a description of the species, its place of origin, habitats and behaviors, as well as fish care to successful maintain them in an aquarium. Fish pictures are also provided within each fish guide to help with identification, and to aid in choosing the best type of Killifish for your freshwater or brackish water fish tank.
For Information on keeping freshwater fish, see:
Freshwater Aquarium Guide: Aquarium Setup and Care
Killifish are small fish with most species being between 2 to 4 inches (5 – 10 cm). There are just a few species that go beyond these sizes. On the smaller side there are some dwarf Killifish. The Dwarf Medaka Oryzias minutillus and the Hummingbird Lampeye Poropanchax myersi are both less than one inch (2 cm). On the other extreme is the largest of the Killifish, Orestias Orestias cuvieri, which can reach up to 10 1/2 inches (27 cm).
Each species of Killifish has its own variety of colors and patterns, and many are extremely attractive. Males are the most brightly colored with the females being duller. Most all of the Killifish have heads flattened on the top. The mouth is either at the tip or in many specimens is underslung, typical of surface swimming fish. They have long pointed teeth that are usually curved. They have no barbels and almost all species have round scales. They have no lateral line but most have lateral line organs chiefly on the head.
Though the body shape and fins vary by species, the dorsal fin is set towards the back half of the body. Also most males have larger dorsal and anal fins than females. Many of the Killifish have slender, almost pike-shaped bodies and are excellent swimmers. Then there are others with short rounded fins on a more cylinder shaped body, and still others that are deeper bodied specimens with long broad well-developed fins.
The Moonlight Medaka or Japanese Rice Fish is included here to find it easily. This fish actually belongs to the Beloniformes order of Needle Fishes, which are included in the Unusual Fish section. But because it has been aligned (and taxonomically classified) with the Killifish for many years, and is also recognized through the common name ‘ Medaka’, we include it here.
The Four-eyed fish or Anableps of the family Anablepidae are also members of this order, but as they are livebearers we have included them in the Livebearer Fish section.
Killifish Care and Feeding
As each type of Killifish will have its own set of requirements, these fish are most often are kept in individual species tanks. In general most of these fish are kept by very dedicated aquarists who are prepared to research the individual species and provide the top quality water conditions and foods it needs. When the needs of these fish are met they can readily be kept in captivity and many will spawn.
The diet of Killifish varies by species. Most are carnivores eating aquatic crustaceans, insect larvae and worms. Having a great appetite for insects and insect larvae, Killifish in some areas have been found to be important for mosquito control. There are some species that are predatory stalking other fish, and some that are omnivores so will include algae in their diet. In the Aquarium they will eat live foods including insects, mosquito larvae, water fleas, and various small worms. They will also eat freeze-dried live food and dry food.
The majority of the Killifish are small fish, and though most are not found in shallow water many of the species kept by aquarists are. Consequently an aquarium for them does not need to be particularly large or deep. Depending on the species and the number of fish you are keeping, the tank size can range from 5 gallons and up.
Be sure to research each species for their own special considerations and maintenance requirements. Then provide an environment that is similar to their natural habitat. Most species are found in water that is soft and slightly acid, but often Killifish can slowly be acclimated to other water conditions. The natural distribution of seasonal species, those that live in small pools or flood plains, can be very specific and can have very extreme conditions. For example the puddles of some species can have an extremely high salt concentration, up to 20%, which makes their environment six times more salty than seawater.
As the males are usually aggressive, the aquarium decor needs to provide plenty of hiding spaces among roots and rocks. The aquarium can be planted and some floating plants will provide a more dimly lit tank. Use a fine gravel for the bottom substrate that is dark in color.
Though they are a few species that will temporarily form schools, most often these fish swim alone or in loose groupings. Behavior is different for each individual as well as each species, but males are often quite quarrelsome. If keeping more than one in a small tank, it is best to keep either a pair or one male with two females. In larger aquariums most species can be kept as a group as long as there are more than three males.