These are presumably Florida flagfish, Jordanella floridae. They come from Florida, but have markings like the American flag, hence the name; they aren't, as some imagine, fish that look like the state flag of Florida!
They are pupfish, a kind of non-annual killifish endemic to North America.
They are excellent little fish from freshwater and slightly brackish habitats along the SE coastline of the US. They're quite hardy, but do best at middling temperatures (around 18-22 C is ideal) so are best mixed with fish that enjoy similar conditions, such as danios and the subtropical barbs. You sometimes see them sold as coldwater fish in the UK, but I suspect that's pushing them a bit, since they are from a fairly warm part of the US. On the other hand, during summer, they do just fine in unheated tanks, and may do fine all year around in such tanks if your house doesn't get too cold.
They are very like dwarf cichlids: males defend nests, protect the eggs, and look after the fry until the fry are free swimming. They don't look after the free swimming fry though. They are territorial but not especially aggressive, and work well in communities with midwater fish.
Males and females are very similar, but females have a distinctive dark spot on their dorsal fin. Males tend to be bigger and more brightly coloured, but that isn't always the case, and certainly isn't obvious with juveniles. Adult size is about 5-6 cm.
Florida flagfish are primarily herbivores, like all pupfish, and need algae-based foods in captivity.
Cheers, Neale
