The fish you have there is PROBABLY of the genus
Microglanis . These are South American catfish that usually don't exceed about 8.5cm (3 1/2 inches). There are a number of species, four of which show up reasonably commonly in local fish stores:
M. iheringi, M. poecilus, M. parahybae, and
M. secundus.
I've kept
Microglanis poecilus in the past and found them to be secretive little catfish that only become active at night. They are decidedly predatory so you don't want to keep them in a tank with fish that can fit into their surprisingly large mouth. As adults they can easily make short work of a guppy-sized fish.
Here's a very good link on these catfish:
http://www.scotcat.com/factsheets/microglanis_iheringi.htm
The other possibility is that you have the Asian Bumblebee Cat,
Pseudomystus (Leiocassis) siamensis. They get to about twice the size of
Microglanis and have the same secretive, predatory nature.
A web page (same author as the link above) for
Pseudomystus is at:
http://www.scotcat.com/factsheets/pseudomystus_siamensis.html