Creatures like tunas and bluefish have elongated, and tapered bodies that allow them to move very quickly, and this is fusiform bodies. Jets, and boats are also designed with fusiform shape to allow maximum speed. The fusiform adaptation allows fish like the albacore tuna to swim at such high speeds that very few predators can catch them. The fusiform shape also allows predators to catch prey. The high speed fish are usually at, or near the top of the ocean food chain.
Sharks are a very good example of fusiform predators.
They can reach very high speeds and have tapered long bodies.