What covers the bodies of most fish and consists of overlapping rigid plates?

The bodies of most fish are covered by scales, which are composed of overlapping rigid plates. These scales serve several important functions, including protection against physical injury and parasites, as well as reducing drag in the water to enhance swimming efficiency. Fish scales can vary in structure and type, with some being more flexible and others being more rigid, depending on the species. The overlapping arrangement of scales also allows for a flexible yet sturdy covering that aids in mobility.

Feathers, fur, and shells serve different functions for other classes of animals. Feathers are primarily associated with birds and provide insulation, waterproofing, and the ability to fly. Fur is characteristic of mammals, providing warmth and protection. Shells, which are hard protective outer layers, are commonly found in mollusks and certain reptiles, but they do not apply to fish. Therefore, the correct answer is scales, as they are specifically adapted for the aquatic environment and the biological needs of fish.