Killifish which are part of the Cyprinodontidae family of fish and also often referred to as egg-laying tooth carp. You do not tend to see them for sale in aquatics shops; they are thought to be more of a specialist can of fish.
Some of the species of fish can be hard to keep. One of the main problems when trying to keep them is their need for soft acidic water. Some species can live in hard alkaline water, but they need to be slowly acclimated to it first. If you intend to breed these fish, they will only breed in conditions closely making their natural habitat. So if you have acclimatised these to hard alkaline water, they will need to be slowly acclimatised back to soft acidic water before you try to breed them.
You need to be careful when conducting water changes as well, as sudden changes to the water chemistry can cause these fish to die of shock. So a little at a time is probably the best policy.
Due to their small size they can be keep in small aquariums , with the larger species needing around a 60 litre aquarium to happy and content. These fish can be aggressive so should be keep in a single variety tank. The males can also be aggressive with each other, so only keeping one per tank is a good idea.
They are also good at jumping out of their tanks; therefore a tank with a tight lid is a must.
Killifish can be broken down into three sub groups; the annuals, semi annuals and non-annuals. These groups refer to waters which these fish inhabit in the wild. Many live in waters which dry out during the dry season. Some areas dry out annually, some semi annually and some do not dry out at all. When the water dries up the fish die, but before they die they breed and lay their eggs in the ground. The eggs survive the dry season, then hatch and grow quickly when the water comes back.
As mention above you rarely see these fish in aquatic shops, but you can buy the eggs mail order. I have seen them on EBay. Alternatively they can be obtained from fish keeping groups, where fish keepers exchange their excess eggs and other fry (baby fish).
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