Have sharks ever been trained

No, sharks are simple creatures that act totally on instinct, and could never be trusted.

Another OpinionI'm not of the opinion that a shark is a simple creature. I would consider an earthworm simple, but the most efficient and deadly predator that has ever lived can hardly be called simple. They have extraordinary senses and an amazingly keen sense of smell. They have a special sense of detecting muscle movement in fish by their sensitivity to electromagnetic waves. Though they may have a small brain, that little brain has to do a lot of complex processing in order to interpret all that sensory information and produce behavior that ends in a successful feeding. They may be simple compared to a rocket scientist, but I challenge any rocket scientist to go underwater and hunt down their dinner with only their senses.