Marine Wildlife Encyclopedia
Ocean Sunfish Mola mola
The ocean sunfish is the world’s heaviest bony fish and has a distinctive disklike shape. Instead of a caudal fin, it has a rudderlike structure (clavus) formed by extensions of the dorsal and anal fin rays, and it swims by flapping its tall dorsal and anal fins from side to side. Its common name comes from the fish’s habit of drifting in surface currents while lying on its side. It also swims upright with its dorsal fin sticking above the surface. The ocean sunfish has no scales, but its skin is very thick and stretchy. Like the porcupinefish, to which it is related, the ocean sunfish has a single fused tooth-plate in each jaw, but it feeds mainly on soft-bodied jellyfish and other slow-moving invertebrates and fish. Females produce the most eggs of any bony fish, laying up to 100 million in the open ocean. Lone fish make grating noises with pharyngeal (throat) teeth, and this may help them to make contact with potential mates.