Killifish are not well known in the mainstream aquarium hobby and are seldom seen in local fish stores, but they are some of the most colorful freshwater aquarium fish in existence. Members of the family Cyprinodontidae, these distant relatives of mollies, guppies, swordtails and platies are known collectively as egg laying tooth carp. Most are small – 1” to 2” – with the largest species growing to less than 6 inches. Most killifish live 2 to 5 years in aquariums.
Perhaps the most fascinating thing about killifish is their different spawning methods, which separate them into three basic groups: annuals, semi-annuals and non-annuals. In the wild, annuals live in temporary pools that dry up each year for periods up to 6 months. They hatch, grow, reproduce and die all in less than a year and their eggs go dormant until the next rainy season. Semi-annuals inhabit areas that may or may not dry up completely, while non-annuals occupy permanent bodies of water. Keeping killifish ranges from easy to difficult, depending on species. While they do have a few special requirements, if you are looking for something a little different, killifish are well worth the effort!
Natural Habitat for Killifish
Killifish are found in tropical and sub-tropical waters on every continent except Australia and Antarctica. They inhabit temporary pools, swamps, creeks and shallow streams, while some species are known to venture into brackish estuary habitats. Many killifish are found in habitats with overhanging trees and shrubs, which create subdued light and cooler temperatures. However, a few species, such as the pupfish of the southwestern United States, inhabit desert pools with water temperatures in excess of 90° F.
Water Requirements for Killifish
While many killifish come from soft acid water, captive bred strains that have been acclimated to local water conditions are becoming more common. Before buying, it is good practice to research killifish carefully to find out what water conditions the fish were bred in. Preferred water conditions vary depending on species, but most killies do well at a pH of 6.0 to 7.0, total hardness between 7° and 10° (120 ppm to 160 ppm) and temperature between 68° and 75° F. Some seasoned killifish keepers do not use filters (they do a lot of water changes!), but for the average hobbyist, a hang-on the back or sponge filter is recommended. Use an Aqueon Aquarium Heater to maintain proper temperature, maintain optimal filtration and perform a 10% weekly water change or 25% every other week using an Aqueon Aquarium Water Changer or Siphon Vacuum Gravel Cleaner. Do not forget to treat tap water with Aqueon Water Conditioner before refilling your aquarium!
Housing Recommendations for Killifish
Many killifish are perfect for nano and desktop aquariums because of their small size. For species tanks, a trio can be housed in 5 to 10 gallons, but a 20-gallon or larger aquarium is recommended for community setups or if you want to keep more than one male. Lighting should be subdued, and non-breeding tanks should be decorated with driftwood or peat moss to help soften the water and lower pH, along with low light tolerant plants such as Cryptocorynes, Java moss and Java fern. Killifish are accomplished jumpers, so a tight-fitting lid is a must!
Behavior/Compatibility for Killifish
Dedicated killifish hobbyists typically keep them in species tanks, but many types can be kept in community aquariums. Most killifish are fairly peaceful, but males can be feisty and sometimes territorial towards each other. There are also a few exceptions to the rule. The Golden Wonder Killie (Aplocheilus lineatus), a popular and often available killie and the Blue Gularis (Fundulopanchax sjoestedti), one of the largest and best-known killifish, can both be aggressive and should be kept alone or with other “spirited” fish. Always research the species you intend to buy before mixing them with other fish.
What Do Killifish Eat?
Killifish are carnivores. Depending on the size of your fish, frozen foods such as brine shrimp, newly hatched brine shrimp nauplii, daphnia, mysis shrimp, mosquito larvae and bloodworms are all good choices. Killifish have a reputation of refusing dry foods, but many hobbyists have had success with them. Aqueon Tropical Flakes, Color Flakes, Betta Food and Betta Treat are all worth a try! Give your fish a variety of foods and feed only what they can consume in 2 minutes or less, once or twice a day.
Killifish Breeding Level – Easy to Difficult
Killifish are egg layers and can be divided into top spawners and bottom spawners, although certain species alternate between top and bottom. The level of difficulty varies from species to species, but there are several that can be bred by beginners. For breeding annuals or semi-annuals, it is best to use a 2½ to 5½ gallon tank with peat moss and/or almond or oak leaves on the bottom.