I'm an absolute killie freak, be forewarned if you read on! I got my first pair at the start of the 1990s, and have been into these colourful fish since then. I consider them ideal for aquarists who like hands on fishkeeping and who live off the beaten path. Because their eggs can be mailed, they are a great equalizer for people who choose to live farther from population (and fish sharing) centres than most of us.
A "killie" is many things. I like the Genus Aphyosemion. My fish live 2-3 years, and lay eggs that take about 2 weeks to hatch. I just keep replacing my adults, raising fry and having fun. One species I keep have been in my tanks since 1992. I still like them, many generations in. And learning how to keep them going that long has taught me more about fishkeeping than a lifetime on forums would.
I'm in Canada, and get my fish from breeders in France, Spain, England, Portugal, Czechia, Poland and the USA, as well as western Africa.
There are issues for these fish. One species, one tank. That's the big one. Temps from 19 to 23c. Highest quality foods needed - the fish equivalent of processed foods don't fly. And you must breed them. They aren't good if you want fish as ornaments. You have to want to participate in a living process.
There are annual killifish = short lived, beautiful and with eggs that can rest unhatched for long periods, as befits fish evolved in wet and dry seasons where their ponds, streams and wetlands dry out. They aren't what I keep, but they are also fascinating.
Another appealing thing to me is these fish, with very few exceptions, haven't fallen prey to the human wish to 'improve". They aren't examples of the linebreeder's art, like fancy guppies or Bettas. Orange australe and some blue gularis have been fancy bred, but 95% of these fish are just as their habitats made them. That to me is cool.
My pictures.