I'm not sure you'll find that the sharks are provoking the oscars to chase. They are just not bright enough to realise they are swimming into trouble. They are fairly skittish fish and the oscars will have a fun time beating them when the O's get bigger. Balas are quite a timid fish in the main. This was my 12" plus Bala, one of my favourite freshwater fish.
Hey PP, i post on the puffer forum every now and then, nice to see you over here on MFK!
If you are talking about the fish Whitelineracer has pictured those are Balantiocheilus melanopterus, only common name i have seen them by is baja sharks. I guess i can see why someone would refer to them as silver sharks though.