Introduction to Killifish
A walk into your Local Fish Shop (LFS) will reveal tanks upon tanks of livebearers, cichlids, tetras, catfish, goldfish, anabantoids even many oddball fish like fire eels or snakeheads but sadly very few species of killifish. This gives rise to the impression that killifish are somehow difficult to keep and breed, this is in fact far from the truth.
Unlike the vast majority of aquarium fish they are adapted to live in very small bodies of water which makes them ideal to keep in fish tanks even small ones. They are generally quite hardy and happy to breed in a wider range of conditions than other groups of fish.
Rather than having large clutches of eggs, most killifish species produce a steady stream of eggs over their lifetime. This allows the breeder to adapt their techniques without catastrophic losses of all their fry. It also means they don’t have to suddenly house large numbers of fish or have lots of empty tanks waiting for fry to grow out. This is also the reason behind the lack of killifish in the LFS. Because of their steady breeding habits they are difficult to culture in the huge numbers on fish farms to make them commercially viable and few species reach the LFS via this source.
One great advantage killifish have over other groups of fish is that their eggs are hardy enough to post even internationally in a jiffy bag on sealed damp peat or coir. This means a wide range of species are available to you with just a little research online. It also means when your fish are successful at producing eggs you have a large potential customer base you can sell them to. This is obviously not the case for most other fish groups that need to be posting as live fish.
Newly hatched fry of starter species are often quite large and can thrive at room temperature in small pots on a shelf without the need for heaters or filtration.
Killifish can broadly be divided into 2 types depending on their mechanism of breeding – annual and non-annual. Annual killifish are specially adapted for seasonal rains. They lay their eggs into the substrate and require a dry period to continue their life cycle. Annual killifish live life in the fast lane, growing fast and breeding fervently before the pond dries up. Even in an aquarium they grow old quickly and rarely live for more than a year. Non-annual killifish by comparison take it easy, they aren’t necessarily short lived in the home aquarium, living to an expected age comparable to other similar sized fishes (perhaps 2-4 years).
Rule number 1 for killifish keeping has to be to use a tight fitting lid on all tanks/containers. Most killies are adept escape artists and every killie keeper has a sad tale of a prize pair of killies being broken up by this miss-hap. You have been warned learn the lesson quickly. Thankfully it is an issue easily resolved with sellotape and cut plastic.
The attraction to killifish is many fold:
- Of course there is their obvious beauty with diverse colouration, patterning and finnage.
- On a practical level, the often small sizes attained by adult fish, many <4 inches (10cm) allows them to be kept in relatively small tanks
- There is minimal heating and lighting requiments for both adult and fry.
- The ability to share eggs through the post even internationally.
With literally 1000s of species to choose from killifish culture can be an interest to last a lifetime. The real joy in keeping killifish is the breeding and raising of fish and killifish are a great group for home fish culture.
Welcome to the fascinating world of Killifish. There is much debate about where the word ‘killi’ comes from and no absolute way of determining the actual origin. It seems to have originated in Dutch settled areas of the United States of America, from the middle Dutch word ‘kil’, meaning a small body of water. But it is now used to encompass all the egg-laying species of the Order Cyprinodontiformes, even some livebearing ones (e.g. Heterandria formosa – the least killifish). Killifish are therefore closely related to livebearers and many aquarists keep species from both groups.
You might be interested to read this article:
The viviparous killifish and the history of the application of the word killifish (Cyprinodontiformes) by Felipe Alonso and Pablo Calviño
Killifish are widely distributed across the globe with the main concentrations being in tropical and sub-tropical zones of South America and Africa. But they are also found in Central and North America, Southern Europe and Southern Asia and extend well into the southern and northern temperate zones. Not just on mainlands but also islands in the Caribbean, Mediterranean and the Indian Ocean. They are not found naturally in Australasia, where the Rainbowfish predominate.
Most species kept by aquarists are relatively small fish, between 3 and 10cm in standard length (SL) which is measured from the tip of the head to the end of the body. However there are also smaller and larger ones ranging from around 2cm to well over 20cm. One of the most interesting facts about Killifish is that their eggs are quite robust and many can withstand being dried out when water levels fall. The embryos can also halt their growth as many as three times so that they can survive even prolonged periods of drought, months and perhaps years and hatch when conditions are suitable again. These are the seasonal spawners who usually inhabit temporary pools or streams and rivers that fluctuate quite dramatically throughout the year. Other killis live in permanent bodies of water and lay eggs quite regularly. Some of the lampeye species will secrete their eggs into natural crevices and fissures, others will spawn in dense mats of vegetation. There are so many different variations that it would be almost impossible to cover them all.
If this ability to survive drying out weren’t remarkable enough, Killifsh have also adapted to survive from sea level estuarine marshes up to to an isolated lake in the high Andes. A determined desire to survive. But this incredible diversity must be taken into account by any aquarist wishing to keep them.