Mystus vittatus, an asian member of the bagrid family known as a banded mystus, 8-9 inch fish, average to low hardness perams , warm tropical temps a good aquarium fish for the 30 gallon plus tank, will eat fish much under 3 inches long though, so not community in the small leagues, though with fish near on a similar size no problem. Primarily carniverous, but considered unfussy. Pretty much like keeping many synos, schilbes etc, not really challenging , but watch em around the little ones. Small tetras and these guys = expensive snack. I shoulnt think they are aggressive though, probably very laid back, but they will eat whatever they can swallow. Psychologically they will need plants caves and cover.
oh dear! they are not community fish at all, they are Pangasius hypophthalmus a fish that is farmed for food in its native countries.. it grows to around 4 feet in length. to be honest i would return them asap. they shouldnt be sold in petshops at all, but they are cheap fish to produce, so they are commonly avialable. they are one of a few tank buster fish that are a problem for fishkeepers they generally get too big fo most poeple as they need tanks of several hundred gallons!
dont listen to advice fom petshops, whenever you buy any fish, make sure you know what you are getting before you get it, if you see somehtng interesting, take its name - scientific name is better if it is available - good shops should know what it is.
*EDIT* ignore me, Mr Git knows better than i do!
[url=http://www.fishkeeping.co.uk/articles_51/fishless-cycling-article.htm] 'CLICK ME' - 'Fishless Cycling' information - how to prepare your new t...