Kingdom: Animalia

Phylum: Chordata

Class: Actinopterygii

Order: Tetraodontiformes

Family: Molidae

Genus: Mola

Species: M. mola

Physical Description

Ocean sunfish have a large body that is compressed and ovular. They are the largest bony fish, measuring up to 3.1 m in length, 4.26 m in height, and weighing up to 2235 kg. They are scale-less, and have a thick, rubbery skin and irregular patches of tubercles over their body. Notably, adult ocean sunfish do not have a caudal fin or caudal peduncle. They instead have a clavus, which is a truncated tail, used more like a rudder than for propulsion. The clavus reaches from the rear edge of the dorsal fin to the rear edge of the anal fin. The dorsal and anal fins of ocean sunfish are tall, and their small pectoral fins point toward the dorsal fin. The dorsal fin has 15 to 18 soft rays, and the anal fin has 14 to 17 soft rays. They also have a small mouth with fused teeth that form a beak-like structure. Ocean sunfish vary in coloration, though the head, back, tips of the anal and dorsal fins, and clavus are generally a mixture of dark grey-brown and dark silvery grey. They have a white belly and sometimes have white splotches on their fins and dorsal side. Adult ocean fish do not possess a lateral line, and only one gill opening is visible on each side, which is located near the base of the pectoral fins

Biology and Behavior

Ocean sunfish are generally solitary, although they are found in groups when being cleaned by other fish. Ocean sunfish use their dorsal and anal fins as their primary means of locomotion. They flap these fins in a synchronous motion, which also allows them to swim on their side. They occasionally swim near the surface, exposing their top fin, and may even jump out of the water in an apparent effort to detach parasites. Ocean sunfish have been observed repeated diving below the thermocline during the day, possibly to forage for zooplankton that migrate vertically. They may also dive below the thermocline in order to avoid predators. Ocean sunfish have also been observed basking at the surface of the water on their side, drifting with the ocean current. This may be an attempt to re-warm core body temperature after diving into colder.

Habitat and Distribution

They prefer the open ocean but occasionally venture into kelp beds and deep coral reefs in order to be cleaned of parasites by other fishes. Ocean sunfish, Mola mola, are found in the temperate and tropical regions of the Mediterranean, Atlantic, Indian, and Pacific Oceans. They are commonly observed off the coast of Southern California, Indonesia, the British Isles, the Northern and Southern Isles of New Zealand, the southern coasts of Africa, and in the Mediterranean and occasionally in the North Sea.