Mola (fish)
Although commonly called sunfish, members of the genus Mola are marine Molidae and not related to freshwater sunfish.They include the heaviest of all bony fishes.
Description
Molas develop their truncated, bullet-like shape because the back fin, which is present at birth, never grows. Instead, it folds into itself as the creature matures, creating a rounded rudder called a clavus. Mola in Latin means "millstone" and describes the ocean sunfish's somewhat circular shape. They are a silvery colour and have a rough skin texture.The mola is the heaviest of all the bony fishes: large specimens reach 4.3m vertically and 3.0m horizontally, and can weigh over 2,700kg.
Molas inhabit temperate and tropical oceans around the world. They are frequently seen basking in the sun near the surface and are often mistaken for sharks when their huge dorsal fins emerge above the water. Their teeth are fused into a beak-like structure, and they are unable to fully close their relatively small mouths.
Ocean sunfish can become infested with skin parasites, so they often invite small fish or even birds to feed on them. Sunfish sometimes breach the surface up to 3m in the air in an attempt to shake off parasites.
Molas are relatively poor swimmers, waggling their large dorsal and anal fins to move, and steering with their clavus. Their food of choice is jellyfish, though they will eat small fish and large amounts of zooplankton and algae as well. They are harmless to people, but can be very curious and will often approach divers.
Their population is considered vulnerable, as they are frequently snagged in drift gill nets and can suffocate on plastic bags, which resemble jellyfish, their main food source.
They breed by producing around 300 million eggs directly into the ocean, which are externally fertilized by sperm into the water column.