Introduction to the World of Killifish

There are more than 1000 species of killifish

There are many types and species of killifish and their classifications are constantly evolving. Diverse types of killifish are native to different areas across the world, and are known to be present in the Americas, Africa, Europe, Middle East as well as some in Asia.

In contrast to the first reaction on the prefix “killi”, these species are in most cases friendly fish. It is believed that the name “killi” came from the Dutch “kil”, “kill” or Middle Dutch “kille” which mean “riverbed, channel.” This connection is due to fact that the natural habitat for most killis are small puddles, shallow, slow running waters, or low ponds. Since some puddles tend to dry out during the dry season, killifish have developed an interesting adaptation for that type of environment. Their eggs can survive without water for some time, with some species’ eggs being capable of surviving without water for a couple of years.

Most often killifish are divided in three categories: non-annual, semi-annual, and annual killifish.

  • Non-annual species live longer but mature slower, and the eggs’ incubation occurs in the water.
  • Semi-annual species live almost as long as non-annual and mature little bit faster. Their eggs’ incubation can be in water or in dry peat (that’s what I do).
  • Annual species live a short life, some of them only 3 months, some 1.5 years, and mature very fast. The majority of them are ready to breed when they are 2 months old. This group requires dry incubation time, and the eggs can survive a long time without water.

When attending tropical fish expos and conventions the most common questions we get from visitors are, “Can I keep killis in community tank?” or “How will killis interact with my ‘so-and-so fish’?” Certainly, as a killifish breeder and enthusiast I would like to see each killis species in their own beauty just by themselves, which is a more natural setting. This will also prevent crossbreeding. Still, in my experience, killifish are mostly a good addition for a community tank. In a big tank with plenty places to hide, killifish will be safe and peaceful neighbors. Enough space and hideouts will prevent males from chasing and attacking each other. Based on my many years of experience in keeping a variety of tropical fish, the behavior of killifish in community tanks is often similar to swordfish.


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