The last member to post above has raised an extremely important issue. Before I comment on that, I second the species likely being Arnoldichthys spilopterus; my knowledge of the African characins is so limited as to be next to nil, but the pictured fish is certainly a characin not a cyprinid.
This fish needs a group of 10-12. This applies to all shoaling fish (some call it schooling). This "expectation" is programmed into the genetic blueprint of this species. When this is denied the fish, it endures serious stress with consequences. Aggression is usually increased; and the fish usually shows a latency to feed--this latter aspect is very telling because a fish that is reluctant to eat when food is available obviously has a real problem.
The aggression is probably the biggest concern here. The fish may suddenly turn on other fish, out of sheer frustration. Sometimes it reacts the opposite, and wastes away until dead. Increased aggressive behaviour though is the normal response. Unfortunately, this causes stress to the other fish in the aquarium. Even if there is no visible sign to the aquarist, the fish is sending out allomones signaling its aggression, and these seriously harm other fish which become stressed, and things just get worse.
On a general note, never acquire a fish for which you have not somehow researched the requirements/behaviours. This can save you a lot of grief, and help the fish, not only the one individual but all the other fish in your tank. The link Wills posted provides data on the fish.