Some were attacked for that reason (my fault) some weren't. The shark kills the fish on a pretty random basis. I've had a few last for up to a few months. I've seen 3 get killed during feeding, a couple when first added, several have disappeared overnight, and I've even seen him turn on a fish for no reason. Once he does this, he wont stop chasing the fish until he corners it.
I'm sure there is a fish out there that would survive. But after seeing my wife get SO upset when she saw the Gerabaldi get killed, and after spending 100's on fish, I'm loosing hope.
It's not that I'm complaining. I built the tank just for sharks, and if that's all I can have then so be it. It's in the black tip's nature to hunt down and eat small fish. However, it would be nice to add some color to the tank.
The idea about the "shark cage" may work, may not. I say "may not" because one of the main things which triggers him to attack is an eratic/distressed fish. I worry he may injure himself trying to get at it. Even if that's not the case, I don't think he'd forget about the fish once released.