What is the purpose of the pelvic fin?

Pelvic fins can serve multiple purposes depending on the species of fish, like sharks use them for balance when swimming and on males they are part of the sexual organs, but fish like the O'opu in Hawaii use them to navigate up stream and stick to rocks in fast-moving water. Almost all fish have some sort of pelvic fin along their stomach.

The pelvic fin can be positioned in different places along the bottom of the fish. In sharks, they are located lower back towards the anal fin, but on other types of fish, they are higher up the body near the head or the pectoral fins.