Altogether, there are some 1270 different species of killifish. Because of living in ephemeral waters, the eggs of most killifish can survive periods of partial dehydration. Most killies are small fish, from one to two inches (2.5 to 5 cm), with the largest species growing to just under six inches (15 cm).

They are useful in aquariums for algae control. A firm cover and a layer of floating plants is best when keeping these fish. Normally, killifish avoid near-surface water to reduce the danger of being eaten by predators.