The ocean sunfish or common mola (Mola mola) is one of the largest bony fish in the world. It was misidentified as the heaviest bony fish, which was actually a different species, Mola alexandrini. Adults typically weigh between . The species belongs to the Mola genus, one of three in the Molidae family. It is native to tropical and temperate waters around the world. It resembles a fish head without a tail, and its main body is flattened laterally. Sunfish can be as tall as they are long when their dorsal and ventral fins are extended.
Adult sunfish are vulnerable to few natural predators, but sea lions, killer whales, and sharks will consume them. Sunfish are considered a delicacy in some parts of the world, including Japan, Korea, and Taiwan. In the European Union, regulations ban the sale of fish and fishery products derived from the family Molidae. Sunfish are frequently caught in gillnets.
The sunfish is a member of the order Tetraodontiformes, which also includes pufferfish, porcupinefish, and filefish, it shares many traits common to members of this order. It is the type species of the genus.
Naming
Its common English name, sunfish, refers to the animal's habit of sunbathing at the surface of the water. Its common names in Dutch, Portuguese, French, Spanish, Catalan, Italian, Russian, Greek, Hungarian, Norwegian, and German (maanvis, peixe lua, Poisson lune, pez luna, peix lluna, Pesce luna, рыба-луна, φεγγαρόψαρο, holdhal, månefisk and Mondfisch, respectively) mean "moon fish", in reference to its rounded shape. In German, the fish is also known as Schwimmender Kopf, or "swimming head". In Polish, it is named samogłów, meaning "head alone" or "only head", because it has no true tail. In Swedish and Danish it is known as klumpfisk, in Dutch klompvis, in Finnish möhkäkala, all of which mean "lump fish". The Chinese translation of its academic name is , meaning "toppled wheel fish". Many of the sunfish's various names allude themselves to its flattened shape.
Taxonomy
Its scientific name, mola, is Latin for "millstone", which the fish resembles because of its gray color, rough texture, and rounded body; this name is also where the genus name Mola and family name Molidae comes from. The ocean sunfish has various superseded binomial synonyms, and was originally classified in the pufferfish genus, as Tetraodon mola. It is now placed in its own genus, Mola, with three species: Mola mola, Mola tecta and Mola alexandrini (previously known as Mola ramsayi). The ocean sunfish, Mola mola, is the type species of the genus.
The common name "sunfish" without qualifier is used to describe the marine family Molidae and the freshwater sunfish in the family Centrarchidae, which is unrelated to Molidae. On the other hand, the name "ocean sunfish" and "mola" refer only to the family Molidae.
The family Molidae belongs to the order Tetraodontiformes, which includes pufferfish and filefish. It shares many traits common to members of this order, including the four fused teeth that form the characteristic beak and give the order its name (=four, =tooth, and =shape). Indeed, sunfish fry resemble spiky pufferfish more than they resemble adult molas.
Description
The caudal fin of the ocean sunfish is replaced by a rounded clavus, creating the body's distinct truncated shape. The body is flattened laterally, giving it a long oval shape when seen head-on. The pectoral fins are small and fan-shaped, while the dorsal fin and the anal fin are lengthened, often making the fish as tall as it is long. Specimens up to in height have been recorded.
The mature ocean sunfish has an average length of and a fin-to-fin length of . The weight of mature specimens can range from , but even larger individuals are not unheard of. The maximum size recorded is in length, and maximum weight recorded is .
The spinal column of M. mola contains fewer vertebrae and is shorter in relation to the body than that of any other fish. Although the sunfish descended from bony ancestors, its skeleton contains largely cartilaginous tissues, which are lighter than bone, allowing it to grow to sizes impractical for other bony fishes. Its teeth are fused into a beak-like structure, which prevents them from being able to fully close their mouths, while also having pharyngeal teeth located in the throat.
The sunfish lacks a swim bladder. Some sources indicate the internal organs contain a concentrated neurotoxin, tetrodotoxin, like the organs of other poisonous tetraodontiformes, while others dispute this claim.
