Killifish

Killifishes, the egg-laying relatives of Guppy, Platy, Molly and Co., got their name from Dutch emigrants who called the little fish found in the small streams (Kil) in their new home in North America Kilvis.

Cyprinodon longidorsalis
© by Heiko Kärst

They are colonizing most continents except Australia and Antarctica. Most species, except Lampeyes, live on the edge of smaller waters and among aquatic plants, drooping or fallen leaves of land plants and roots. They also spawn there. As these areas quickly become dry as water levels are dropping in dry season , killi eggs have a rigid shell. They are therefore very well protected against drought and can withstand some pressure. A healthy killi egg cannot be accidentally crushed between two fingers, except shortly after spawning.

Species that live in regularly low water levels for a longer period of time or completely dry out have adapted to these conditions. They are called annual species or seasonal fish. The eggs of these species take intervals in their development and can therefore survive droughts. For some eggs this can last several years. This is only possible if the eggs lie well protected in the soil. East African Nothobranchius presses itself on the ground during spawning and separates eggs with a jerky floating movement, thereby the egg is driven into the soil.

Gnatholebias zonatus 'El Baul'
© Frans Vermeulen

Most South American bottom spawners do it differently. The male selects a suitable spot and tries to lure a female over there. If he succeeds, it dives vertically into the ground up to the pectoral fins and waits for the female. If she follows, often she decides otherwise, she touches the male at the pectoral fins and both disappear into the ground to lay their eggs. Compared to Nothobranchius ,which only need a thin layer of spawning substrate (e.g. peat dust, peat granules, coconut granules or fine sand) in the tank or in a shallow bowl, it must be at least as thick as the body length for the bottom divers. In order not to need too much substrate, you can use an appropriate container (e.g. a flower pot or a glass). To prevent that too much substrate is being thrown out during immersion, you can also try a "starling box", i.e. a container that has an opening at the top of one side. But this does not necessarily work for every species and not always immediately.

After spawning, the substrate, usually peat or coconut granules, must be dried to a low residual moisture content. How much exactly is hard to say, it should still be darker, but not stick to your fingers when you touch it. The time after the peat can be wetted again varies from species to species. In most cases it's about 2-4 months.

Moema quii
© by Heinz Ott

For fish that live in an environment that only carry water for a short time per the year, it makes no sense to equip them with genes for a longer life. Others are more important: Grow as fast as possible, become sexually mature and place enough eggs in the soil before the dry season begins, to ensure the survival of the species.

In contrast to the ground spawners, the non annual species lay their eggs in plants, algae or fine roots. These eggs usually have fine adhesive threads with which can attach them to the substrate. The young fish of these species usually hatch after 2 to 3 weeks. In the aquarium you can breed these species with a so called wool mop. On a floating device (e.g. a cork, a piece of polystyrene) wool threads extend down into the water.

Aphyosemion elberti 'Pondemoun'
© by Olaf Deters

The fish except this well and you can collect the eggs to let them develop in a bowl in water or on damp peat or some moss.

The fish except this well and you can collect the eggs to let them develop in a bowl in water or on damp peat or some moss.

A special case are Lampeyes. While most of them, like the well-known Poropanchax normani, are plant spawners, the Procatopus species and also the Tanganyika Lampeye (Lamprichthys tanganicanus) are so-called column spawners. There eggs are usually a bit bigger than the crevices in which they are literally shot into, so that they penetrate as deeply as possible into the spot. Because the eggs swell up a bit after spawning, they are not so easy to get out and well protected against predators. For their spawning, , filter foam has proved to be a good choice for these species.

Aphanius richardsoni 'Neot HaKikar'
© Barbara Nicca

Aphanius, native to the Mediterranean, and Cyprinodon, native to North America, have adapted to extreme water values. Most of these occur in waters that are heavily enriched with minerals, meaning it can have twice the salt density of seawater and can be as hot as 40°C.

Many of the North American Fundulus species inhabit the sea, but also swim into rivers and streams. One species, Fundulus heteroclitus, is known for its tolerance to toxins. In waters that are heavily polluted, it is often found as the only fish species that still lives there. It was also the first species of fish to go into space in 1973, with the NASA Skylab.

Nothobranchius rachovii 'Beira Airport MZCS 08-96'
© by Hristo Hristov

Since killifish are permanent spawners, they should be well fed regularly. Best is to provide pond food, as it has lots of variety ,but frozen food is also ok and after getting used to it most species even take dry food, although I prefer to give granulated food. In general it is no problem to leave the animals without food for a few days, you should only separate the sexes and only put them back together when the females have become round again. The first food for fry should do movements to trigger their reflex. Most young fish take Artemia nauplii or Microworms immediately after hatching. Some species fry are so tiny that they prefer Rotifers or other protozoans in the first days .

Most killifish have a strong difference in appearance between the sexes. The males are more colourful than the females and are usually larger with bigger fins. This shows how the females choose with whom they want to mate: The males have to dress up to have a chance.

It is usually no problem to keep killifishes as a pair or even several males with only a few females, depending on the specie and the space. You have to choose the aquarium big enough and build in enough hiding places and optical separations (plants,roots,etc.).

Fenerbahce devosi 'AVD 2007-2'
© by Heinz Ott

Most killifishes are not fish for Nano tank! You can have them in small tanks for breeding, but always under control and always with the possibility to separate the female from the male. It is also important to cover the aquariums well, because killifishes are good jumpers and can find the smallest gaps in the cover.

At present, 1138 killifish species are recognised as valid, and the trend is rising. On one hand, the destruction of the primeval forests brings us new species again and again, where scientists and interested laypersons come to places that were previously inaccessible, but on the other hand, more and more biotopes are being irretrievably destroyed and with them the fish living in them.

Callopanchax occidentalis
© by Olaf Deters

New scientific findings, especially the possibility of DNA testing, are also bringing changes to the list of killifish species. Therefore, killifish keepers are interested in passing on their fish with a locality code and breeding these locality strains purely , as it happens quite often that individual locality of a species is described as a new species.



*** Translation from German with www.DeepL.com/Translator (free version) ***