I've noticed recently a number of posts on this forum and others, where certain subtropical fish are being mistaken for normal tropical fish. I've therefore decided to give a short list of some of the subtropical species available in the aquarium trade, and a link to where I got information on some of the less obvious species.
For these species temperatures between 18-22 Celcius, or 64-72 F is essential. When the tempreatures are too high their metabolism speeds up and they tend to be more susceptable to disease and stress and have a shortened lifespan. They are less able to cope well with the decrease in oxygen found in warmer waters. Equally however they are not suited to temperatures that are too cold like true coldwater species are, so it's important to still keep an eye on the thermometer during winter time, and provide a heater at the lowest setting if necessary.
Some of the species are:
Corydoras paleatus (peppered cory)
Tanichthys albonubes (white cloud mountain minnow)
Barbus conchonius (rosy barb)
Barbus semifasciolatus (green barb)
Macropodus opercularis (paradise fish)
Gastromyzon punctulatus (hillstream loach)
Gambusia affinis holbrooki (mosquito fish)
Some others that I came across at this link that i didn't initially think of or know off:
Barbus gelius (dwarf golden barb)
Heterandria formosa (dwarf mosquito fish)
Xiphophorus variatus (variatus platy)
Aphanius iberus (spanish kilifish)
Enneacanthus chaetodon (black banded sunfish)
Salaria fluvialitis (FW blenny)
Rhinogobius duospilus (dragon goby)
Some goldfish, more so the fancy varieties, are able to withstand subtropical temperatures also, though best kept at the lower range.
The link: http://www.wetwebmedia.com
Hope this was useful to somebody. :)