They're used to prevent rolling, stabilize their body, and assist in sudden turns. Some fish also use their dorsal fins to display their mood, health, or social status. For example, some fish raise their dorsal fins to show aggression or dominance, while others lower them to show submission or fear. Some fish do not have dorsal fins because they have evolved in other ways to adapt to different environments. For example flatfish and rays, do not have dorsal fins because they do not need them for either stability or maneuvering. Instead, they have evolved to have flattened bodies that help them camouflage and hide from predators rather than relying on movement which would have necessitated the fin.
