The name Killifish is derived from the Dutch word “kilde”, meaning small creek, or puddle. Most killies are small fish, from 2.5 to 5cm, with the largest species growing to just under 15cm. They comprise of a group of fishes of the family Cyprinodontidae and are commonly known as the egg laying tooth carps, cousins to live-bearing fish such as mollies and guppies. Like their live-bearing counterparts, killifish are usually mosquito larvae eaters. There are about 350 species of killifish found within the equatorial belts throughout the world and the occur in practically all regions except Australasia. Many killifish species are as lavishly colored as salt-water fish and have incredible finnage.
In the wild most species are territorial by nature, the male defending his area against intrusion by other males. They mate with whichever females they can tempt into their territory. In the aquarium, it’s best to keep a ratio of one male to two or three females. If you put three males in the tank with enough females to satisfy them all, you’ll avoid too much aggression. Killies are excellent jumpers, so their tank needs a closely fitting lid. In their natural environment most killifish live in soft and slightly acidic waters (pH 6.2-6.8) with temperature ranging from 22 to 26° C.
Killifish are divided into three general breeding groups: annuals, semi annuals, and non-annuals (plant spawners). In the wild, the annuals spawn every day, because in nature, when the pond dries up, the eggs go into a hibernation phase known as diapauses. When the pond fills with the rains from the next season (sometimes 6 months later) the eggs hatch and it isn’t long before the whole pond is filled with killifish. Spawning is done every day, just in case the first rains of the next rainy season are insufficient to fill their pool. By spawning daily (2-3 eggs or more), they ensure that the hatching of the next generation of killies are spread out over time. Species of annual killifish therefore grow and mature very quickly, so they can repeat the process before the ponds dry up again. Killifish that come from areas that are wet year round, such as streams, ponds, and swamps, tend to live longer, some as many as 5 years or more.
Semi-annuals live in areas which sometimes dry out to moist mud, but at other times retain water throughout the dry season. They are therefore substrate spawners, leaving their eggs in the mud and leaves of their habitat. They tend to live a little longer than the annual species of killifish. Semi-annual killifish eggs can be water incubated, but have higher hatching rates if they are stored in moist peat for 30 -60 days. After this ‘drying’ period, one puts the peat and eggs in water and within a few days’ baby fish hatch. While Semi-annuals generally tend to be substrate spawners, they will spawn in peat moss, Java Moss or in spawning mops placed at the bottom of the aquarium.
The non-annuals, such as the Aphyosemion genus species of killifish, live in permanent bodies of water and, in some cases, will live for up to five years. These species are more difficult to keep and require more for successful breeding and raising. The non-annuals, or plant spawners, are usually bred using the spawning mop method for higher yield, and with water incubation of the eggs. Most non-annual killifish eggs hatch on an average of 21 days or so.
Killifish are both easy and complex to breed – complex mainly because of their unique breeding cycles, which requires quite a bit of dedication. We are currently preparing a more informative article on the breeding of Killifish, and will post it as soon as it is ready!
Meanwhile, on the next pages you will find some stunning Killifish images by renowned fish photographer Hristo Hristov, perhaps enough to make you fall in love with this incredibly beautiful and inimitable species. Since Hristo so generously gave us permission to share his beautiful images with you, we will appreciate it if you in turn will honour his generosity by refraining from copying them from our pages.