As with any shoaling fish kept singly or in a group which is too small, it is not possible to predict how it will behave. Some will just hide away and slowly fade and die. Others become aggressive and terrorise a tank. All degrees in that range are possibilities. Whatever applies, the fish will be highly stressed and not live it's normal life span, often turning over fairly quickly.
In a group of 4-5 in an adequate sized tank for a fish that can grow to 6"/150mm it is a peaceful, colourful, moderately sedate fish but does require some open swimming space, it is not as frenetic as some other barbs though. Will eat ordinary food but as with most fish, should be offered a varied diet. They like some vegetable matter, peas are a favourite.
They do not tolerate pollution, so good water quality is important.
Even in a decent sized group, and well cared for, they have a habit of "just dying" for no apparent reason. Gada had 5 I think, but they have slowly died. I'm not sure she has any left now.
Beautiful fish.