Final answer:
The fins of ray-finned fish are made of live tissue that includes webs of skin supported by bony spines, unlike scales which are protective external plaques. These fins allow for precise movement, even though they lack muscles, as the ray-finned fish control them using muscles in the body wall.
Step-by-step explanation:
The fins of ray-finned fish, which include species such as goldfish, tuna, and salmon, consist of live tissue. This live tissue forms webs of skin supported by flexible bony rays, essentially a series of spines. These fins are a critical part of the fish's anatomy, allowing for movement and maneuverability in water. In contrast, scales are individual external plaques that serve as a protective outer layer. The ray-finned fish's fins are indeed live tissue and contain blood vessels and nerves, unlike the overlapping scales which cover the body of many bony fishes and serve different functions including protection from predators, injury, and infection.
In relation to their functionality, the ray fin allows these fish to have precise movements through their aquatic environment. Despite lacking actual muscles within the fins, their movement is controlled by muscles located in the body wall. This provides an effective method for the ray-finned fish to navigate and orient themselves in water, which is vital for activities like foraging and avoiding predators.
To compare, lobe-finned fish have fins that are fleshy with bone and muscle within, giving them a different appearance and function. However, in the case of ray-finned fish, the structure serves as an evolutionary adaptation that enables the fish to have a lightweight yet strong support for fin movements.