The fascinating Killifishes have managed to attract a dedicated fan club worldwide. Killifish is still quite uncommon in traditional pet stores and contacting a breeder directly can therefore be necessary if you want to purchase Killiefish. You can also use the Internet to locate Killifish for sale and participate in Killifish auctions online. Well stocked aquarium shops will sometimes keep a few of the most common Killifish species, typically Aphyosemion australe,Fundulopanchax gardneri and Fundulopanchax sjoestedti. The fact that Killiefish are rare in traditional pet stores does not mean that they are for expert aquarists only. There are actually many Killifish species that will do well even in the hands of a novice aquarist, and getting Killifish into spawning condition is not very difficult.
The Killifish species are tooth carps found in the order Cyprinodontiformes. The name Killifish is sometimes instead spelled Killiefish (with an “e”), but Killifish is the original spelling. The name originates from “kilde”, a Dutch word meaning small creek or puddle. It is a fitting name since Killifish are often found in creeks and puddles. They do however live in larger streams and lakes as well.
Most Killifish species are comparatively small and the fish typically stay between 2.5 and 5 centimetres (1 to 2 inches) in length. The biggest known Killifish species grow up to nearly 15 centimetres (6 inches).
Killifish inhabiting seasonal puddles and lakes that vanish during the dry season will typically have a very short lifespan even in captivity. In the wild, they rarely live for more than 9 months and even though they will survive longer in the aquarium you can not expect them to survive for any longer period of time. Killifish inhabiting permanent bodies of water will typically live for 2-3 years.
Wild Killifish can be found in Asia (including the Middle East), Africa, North America, South America and southern Europe. In the United States, the northernmost populations of wild Killifish are found in southern Ontario. On the South American continent, Killifish can be found all the way down to southern Argentina. In Africa, Killifish can be found all the way down to Kwa-Zulu Natal in South Africa. Killifish live in freshwater streams and lakes, but can also be found in brackish conditions.
Since Killifish can be found in such dissimilar parts of the world, they naturally have varying requirements in the aquarium. It is therefore very important that you research the particular Killifish species that you are interested in before you make a purchase. Conditions that are ideal for one species of Killiefish can be quite harmful to another species.
One of the things that vary considerably between the many Killifish species is their required diet. Some species are carnivores and must be feed meaty foods in the aquarium, e.g. fish and insects. Some prefer live food, while others readily accept dead food without much coaxing. Other types of Killifish cannot be kept on a diet of fish and insects, since this is not their natural diet. There is for instance the plankton feeding Killiefish species.
Many Killifish species are considered easy to breed in captivity, but you must first find out their reproductive method since you might have to imitate the factors that induce breeding in the wild. Since Killifish species inhabit so many different types of environments, they have developed several different reproductive methods to insure the survival of their offspring. Some Killiefish species are egg scatters that will appreciate a planted aquarium. If your particular Killifish species inhabit rocky environments, they might instead be cave spawners that deposit their eggs in caves and crevices. Some Killifish species will form their own nests rather than using plants or caves as breeding sites.
One of the most famous reproductive methods used by Killifish is however the egg burying method. Killifish species that inhabit environments highly affected by alternating dry and rainy seasons have developed a way of making their eggs survive throughout the drought, even if the shallow puddle where they fish live dries out completely. The adult fish will bury the fertilized eggs deep down in the mud while there is still water in the puddle. If the puddle dries out, the adult fish will die, but the eggs will survive deep down in the dirt. As the rains return, the eggs will detect the changed environment and hatch. This means that the fry will emerge at the beginning of the rainy season when water and food is abundant.
If you wish to keep Killifish that inhabit seasonal puddles in the wild, you should be aware that their natural lifespan is very short. In the wild, such species rarely survive longer than 9 months. You can make them survive longer in an aquarium since their home will not dry out, but they are genetically programmed to have a short life.
When we discus the reproductive strategies of killifish we must also mention the fascinating species found in the genera Campellolebias and Cynopoecilus. Unlike the other Killifish species, these fishes use pseudo-internal fertilization. Killifish from this genus might therefore provide us with an explanation of how egg laying species gradually developed into livebearers. The Campellolebias and Cynopoecilus species might be a link between the egg-laying and livebearing tooth carps. The male Killifish found in these two genera are equipped with a gonopodium, a reproductive organ that is used to fertilize the eggs.
If you are interested in the reproductive methods of the Killifish species, you should deficiently take a closer look at the Kryptolebias marmoratus. This is the only known vertebrate capable of real self-fertilization. No female specimens have been found, and it seems as though fish from this species is either male or hermaphroditic. No more than roughly 5 percent of the offspring is born male. After 3-4 years, around 60 percent of the hermaphrodites will turn into so called “secondary males” and loose the female structure and function. The amount of malesis affected by temperature, and in waters where the temperature is below 20° C (68° F) you will find that a majority of the specimens are male. In waters where the temperature is above 25° C (77° F), all the specimens will be hermaphrodites. This species is unfortunately very hard to keep in aquariums.