Jacks are voracious predators and are most active just after sunset when they feed on reef fish. Sharks and jacks are both fishes, but spend a few minutes comparing them and see how different they are from each other. Look at the shape of the fins. Notice, too, how different shark's and jack's tails are. And internally, sharks have lightweight skeletons made of cartilage much like the material in our ears.
Jacks have skeletons made of hard mineralized bone similar to our own.
These hunters on the reef are truly among the most magnificent animals in the sea.