Final answer:
Fast swimmer fish have a fusiform, streamlined body shape that reduces drag in the water, enabling them to swim quickly. Sharks and dolphins are examples of fast swimmers with this body form.
Step-by-step explanation:
Fish that are fast swimmers tend to have a fusiform body shape, which is tubular and tapered at both ends. This streamlined body shape is highly adapted to reduce drag as the fish moves through water, thus allowing it to swim at high speeds. For example, certain types of sharks can reach speeds of up to fifty kilometers per hour, and some dolphins can swim at 32 to 40 kilometers per hour. The skin of bony fishes is often covered with scales, and they secrete mucus that helps to further reduce drag. Additionally, these fishes possess a lateral line system to detect vibrations, and their fins and swim bladders are also adapted for efficient movement in water.