Are you serious? I've never heard of this. People buy minnows as exotics? What's a Pup fish? Can you tell us more?
There's a bunch of "pupfish" (related to kilifish / Fundulus) Genus Cyprinodon. Some are isolated to single sink holes in the desert southwest. Some have much wider ranges including brackish to saline conditions through out the South/ Southeast US and into the Caribbean Islands. Maybe extending up most of the Eastern seaboard. We actually use the most common species, Cyprinodon variagatus, in our lab to conduct salt water toxicity tests. They are very easy to culture in both fresh and salt water.
I don't know how many different species there are, but they are superficially similar. The biggest species may be about the size of a US quarter, and the smaller species maybe the size of a US nickel at maturity. Females are dull brown, Breeding males in various shades of metalic blue, green, and maybe some red and yellow highlights. You can actually transport the eggs in damp paper towels (no standing water) and hatch them out after several days without water.
One time I had a breeding group collected from Turks Caicos. They looked like pigmy versions of the common variagatus. I had them in 33 ppt salt water, but I needed the tank for something else, moved them out of the tank, filled it w/chlorinated tap water for a day, drained and filled with dechlorinated water for the next group of fish I was going to use the tank for.
Over the course of a week, I ended up with about 50 baby pupfish hatching from the gravel in the bottom of the tank! Tough buggers!
Any way some of the rarest are the isolated desert species (famous for heat tolerance). A population of Desert pupfish (Cyprinodon diablo) is found in Death Valley National Park. A couple of other endangered species are found in isolated sinkhole systems in Nevada, Arizona, and N Mexico. They tend to be on private ranch land in out of the way remote areas. I know at one time the Nature Conservancy had bought some cooperative easements around the sinkholes. Several public aquariums had started an SSP (Species Survival Program) with them to artificially propagate.
I was involved with a similar SSP for Lake Victorian Cichlids at the same time as other zoo/aquariums were working with the native species. The Lake Victorian Cichlid SSP produced so many fish (some of which extinct in the wild) we ended up dumping into the retail aquarium trade for maintaining tank space. I don't know if the other SSP's were equally successful since I have left the zoo biz.
I believe there there are still national and international Cichlid and Killifish associations. When I was active in aquaria the German's and Japanese were particularly interested in these fishes (not unlike orchids).
Killifish are really good for international trade since you can transport eggs in damp moss or paper towels. Most species live great at room temperature, in small tanks with no filtration.
