Killifish are great 'little' fish and certainly have some of the most colorful species in fresh water. Unfortunately most of the larger fish stores rarely get them in primarily because most people aren't familiar with them so they aren't big sellers. They are found in North and South America, Africa, Eurasia and Australia.
The thing you have to be careful about when going 'killi' shopping is that you don't buy the 'annual' killifish. These magnificently colored fish have a very short lifespan...usually a year or less. There are many people who specialize in breeding the 'annuals'...so they keep a constant supply of them to replace the adults as they pass to that great fishy paradise in the sky (or whereever it is).
The
Aplocheilus species like
A. lineatus and
A. dayi occasionally show up at the
lfs as Punkymom has found. They are NOT 'annuals' so they're a bit more popular with folks who are not 'killi' specialists. Give them a nicely planted tank with neutral to slightly acid water and they'll color up beautifully. A few cautions are in order, however. Some of the
Aplocheilus can be fin-nippers (though not in the same class with Tiger Barbs) and they will eat any fish small enough to be swallowed. They are primarily surface feeders so sinking food will often be ignored. They do benefit greatly from live food like Daphnia or brine shrimp (and maybe the occasional guppy fry). You might also try wingless fruit flies.
As I mentioned earlier in this thread (and as Punkymom discovered)...many of the killifish are consummate jumpers and their tanks need to be covered as completely as possible. I offer the following excerpt from
Exotic Aquarium Fishes by Dr. William T. Innes. This regards the Blue Gularis killifish,
Aphyosemion (Fundulopanchax) sjoestedti but can be applied to almost all of the 'killis':
As a postscript regarding the jumpiness of this fish, it is recalled that many years ago a fellow enthusiast and the author imported a score of them. Prior to dividing them they were placed over night in a larged covered trough. The lid was a half inch short of complete coverage. By morning every fish had leaped out and dried out!