A killifish is one of a large group of fish called Cyprinodontidae or tooth carps. The name “killifish” originated from the word “kill” which in old Dutch means “channel”. Simply, killifish are fish which are found in channels of water. The Cyprinodontidae group includes the anableps, the silversides, the live bearing tooth carps and the egg laying tooth carps. They are often referred to as egg-laying tooth carps to differentiate them from their closest relatives live-bearing tooth carps being guppies, mollies etc).
These fish are found on all continents except for Australia. They differ from continent to continent. In simple terms they are divided into three groups; the annuals, the semi-annuals and the non-annuals.
In the wild the annuals live in non-permanent pools that dry up in summer. They lay their eggs in the mud at the bottom of the pool before the pool dries out and the fish die. When the rains come the fish eggs hatch, the fry grow and mature so that in a period of six weeks they are able to lay eggs again. In a cool aquarium these fish live for much longer and will spawn for 12 months or more. They are often quite easy to breed and are the most interesting fish. Semi-annuals live in pools that occasionally dry out in the dry season. The nonannuals live in permanent water masses and may live up to 5 years.
In terms of their breeding habits, killies are usually classified into two principal groups — the plant spawners and the bottom spawners. The plant spawners lay their eggs on the roots of floating plants and other aquatic vegetation, whereas the bottom spawners lay their eggs either on or within the bottom litter or detritus of their natural habitat. Killie breeders deal with these two situations by providing spawning mops, made of nylon or acrylic yarn, as a spawning medium for the plant spawning species and peatmoss as a medium on or into which the bottom spawning species may lay their eggs.
In the case of the plant spawners, the eggs are picked from the spawning mops daily and stored in containers of water until they hatch; usually two to three weeks for most species. The eggs of bottom spawners require a period of drying to complete their development, so peat is collected from the spawning tank every two or three weeks, partially dried and stored in plastic bags in a warm, dark place for periods, depending on the species involved, of anywhere between two and ten months.
At the end of this time, the peat is placed in water, and the fry hatched within a matter of hours. There is probably no more dramatic and exciting event in aquaculture than to witness perhaps hundreds of fry hatch, as if by magic, from dry peat that has been months in storage to a fish-tank full of life!