Killi is the popular name for a large range of species from the scientific order Cyprinodontiformes. At this state more than 600 different species and strains are known as Killi so it is necessary to give every strains their precise scientific names. For beginners who have some experience from the community tank, it can seem quite difficult with all the Latin names, but the more you learn about the killies, the more easy the Latin names comes to you. Not many of the Killi species have a popular name as popular names are often something comes from the fish-shops and not from the hobbyists. Killi keepers prefer to keep the scientific names because the Latin name precisely states which fish we are talking about.
The name KILLI is not referring to the word KILL as most of the killies are actually quite calm and relaxing fish. The word Killi is from the Dutch language and simply means "water source" or "stream".

The reason of choosing the Latin language when naming the kilies is that it is a dead language and does not change as time goes by.
All of the killies are inside the order Cyprinodontiformes so this is not mentioned in the name. The family could be stated as e.g. Aplocheilidae, Rivulidae or Fundulidae but in general we do not mention the family either.

In daily talk we first of all mention the genus (e.g. Nothobranchius). Inside each genus there are several species. Following we have to clarify which species inside the genus Nothobranchius we are referring to. This is done by the species name (e.g. Guentheri). Then we have a genus and a species Nothobranchius Guentheri and now we have the aquarium strain name of the fish.
But each species has different strains after their geographic location. If the collection location is known (which is very important for the very dedicated killi breeders) this is stated after the genus name and species name. For instance Nothobranchius Guentheri Zanzibar TAN 97/2.
This is a very clear name that explains the genus, species, collected in Tanzania in a geographic area where Zanzibar is the closest village or town, and it is collected in 1997 (and kept isolated so the fish/eggs directly originates from the parrents collected at the location). The last digit /2 is a collection code made by the finders to specify the strain. Maybe they have collected Nothobranchius Guentheri from several ponds while the closest village still was Zanzibar. But this is very very technical and exactly what is frightning most beginners. If you just start learning the genrea and and afterwards the species you will know much more than a lot of killi keepers.

As the group of Killi fish is so enormous it can be difficult to give overall information. But general for all of the killies is that they live in small rivers, streams, swamps, etc. Even in very small ponds for some species.
It is possible to find killies all over the world except Australia, though most of them from the tropic regions in South America and Africa. But also North America, Europe and Asia has its own fish. The killies are generally quite small compared to e.g. cichlids, but at least as colourful and in my opinion more interesting and easy. Generally speaking the adult killies are from 2 cm to 15 cm so almost every aquarist has the required space for a killi. All of the killies are egg laying but can be divided into annual, non annual and semi-annual fish.

The annual killi or “season fish” are quite short lived but very interesting. Nothobranchius Rachovii is a good example of an annual Killi and is shown here to the right.
They live in locations where the summer season dries out the water they are living in. Following they have to grow very fast to manage to place eggs in the soil before the dry period comes. When the parents are dead, the eggs in the soil are the future of the species, and the eggs will hatch when the dry period is over. When the rain comes back and fills the water hole or stream again the eggs will hatch and the cyclus will be repeated. You might think – “what if the rain is only a temporary shower? – Will the eggs then hatch and the fry die when waterhole will dry out again ??” No, the fish has absorbed to this strange weather conditions and eggs will hatch in more steps. Some eggs are programmed to hatch after a certain dry period at the first water upon the soil. Then other eggs are programmed to hatch 2nd 3rd and 4th time the soil is under water so even if the stream dries out several times in a season, the species will survive. The dry period of the eggs makes trading with annual killi eggs possible for all over the world. You can find the dry period of the eggs in species description and how to do in the Starting with killi information. Please note that even if your aquarium will not dry out in the summer period the adults will not live longer. Following you will have to collect and dry eggs if you want continuous pleasure of your annuals.

The non annual killies are more like “ordinary” aquarium fish and the Aphyosemion celiae celiae shown here to the right, is a good example of a non annual killi. They live for several seasons and the eggs does not need a dry period. Actually some of the non annuals are known to fill up a tank if given the right conditions. The eggs are placed in thin leaved plants, in the gravel or in spawning mops and will hatch after some weeks. But again - it depends on the genus and species how sucesful and easy they are to make breeding. See more under the species list.

The semi annuals are fish of which the eggs can be dryed for the egg developement. Some of the fish known as non annuals are actually semi annuals as you can pick the eggs and dry them for a shorter period. The reason of doing this could be that you want your fry to hatch at the same time so the fry are most possible of same size. When the eggs from non annuals are hatching in the aquarium you can experience that the eggs are hatching over a long period. This will result in larger and smaller fry in the same tank. In such situation the youngest fry could have problems in developement as the older fry wil be faster and more greedy. Even in some species the new hatched fry will just be a good live food for the elder fry. If you make the eggs develope in moist peat and then pour water over the peat, your will have a more homogeneous hatch. But please note that it is far from all eggs of non annuals which can stand a dry period. Check the species description before drying your eggs. An example of semi annual is Fundulopanchax gardneri. The eggs of the gardneri can easily be stored for a week or 2 to let the eggs develop.

In all 3 groups there are more or less colourful species but almost in any strain the male is more beautiful than the female. Actually you have to be very experienced to determine the strain of a female as most of them are quite similar - at least inside each species. The males are often a bit bigger and have more colours or drawings than the females. A good example is the Scriptaphyosemion Liberiense as shown here, although the difference is even more clear in my tank than on the pictures.

As a beginner the killi trigger is often the extreme colours you do not often see on other fresh water fish. But the colours are not all. Just watching the behaviour of the different species is very interesting and I can assure you that no matter what killi you choose as your first one, it will bring a smile on your face now and then.

As a killi hobbyist it is not clever to mix more killies in each tank. Unfortunately some species are endangered and following it is very important to keep the species clean. The different killies can be mixed if having 2 from same genus in the tank. The hybrid fry can be sterile and are not well seen in the hobby. Following most of the killi keepers either split up their current tanks in more small rooms or have several smaller tanks. One room for every strain.

To have the greatest success it is good to give the fish the best tank setup. Many of the species are quite hard and will survive unde even hard conditions. But please remember that some fish are from dark water streams in the forest and are not used to that much direct light. Other species are used to very cold water, etc etc. In order to make the best – give them the best. Please study the species carefully before buying the fish so you are sure that you are able to give what it takes. Actually this is general for all of the aquarium fish we bring home.

AnnualNothobranchius Rachovii
Copyright Geert van Huijgevoort

Non annualAphyosemion celiae celiae 'Teke
Copyright Geert van Huijgevoort

Semi annual Fundulopanchax gardneri