Family MOLIDAE


Common name: Ocean sunfishes

Silhouette

Summary:

Ocean sunfishes are the largest bony fishes in the world. These breathtaking oceanic giants have deep compressed bodies, high dorsal and anal fins at the rear and a truncated tail region. 

Instead of a caudal fin, molids have a clavus (meaning rudder in Latin) – a deep, stiff lobe at the end of the body formed from extensions of the dorsal and anal fin rays. Molids also lack pelvic fins, ribs, a swim bladder and have fewer vertebrae than any other bony fishes.

Mola mola, the Ocean Sunfish, grows to more than 3 metres in length, 4.2 metres in height, and can weigh more than 2 tonnes. Much of what is known about ocean sunfishes has come from stranded individuals.

Key to genera in the family of Molidae

1    Body moderately deep, its greatest depth 49–54% of standard length, more or less oblong; skin smooth with small hexagonal scutes; pectoral fins elongate; lips funnel-like, closing as a vertical slit; body generally silvery……….……………………………………..........Ranzania

Body very deep, its greatest depth 58–80% of standard length, oval or almost circular; skin rough textured, covered with denticles, hexagonal scutes absent; pectoral fins small, rounded; lips not funnel-like, closing in rounded form; body rather ………...……………....................2

2    Clavus with distinct median extension, remaining margin not scalloped ………….. Masturus

      Clavus with no distinct median extension, margin mostly scalloped .............................. Mola


Cite this page as:
Dianne J. Bray, Ocean sunfishes, MOLIDAE in Fishes of Australia, accessed 15 Dec 2017, http://fishesofaustralia.net.au/Home/family/186

More Info


Family Taxonomy

A small family of large oceanic fishes  with four species in three genera. Ocean sunfishes are found worldwide in tropical to warm temperate waters, and all species occur in Australian waters.

Family Distribution

Widespread in tropical and temperate waters worldwide, usually in the open ocean far offshore. Mola mola, the most common and widespread species, spends most of its time in the top 200 m of the ocean, often basking at the surface, flapping its dorsal fin out of the water. 
Once thought to be a sluggish, sedentary species, Mola mola is actually an active swimmer, regularly diving to depths below the thermocline. One fish was recorded to dive to a depth of 844 m.

Family Description

Deep-bodied fishes, with high dorsal and anal fins, a reduction and fusion of caudal fin elements resulting in a loss of the caudal fin, a clavus or rudder-like structure, no swim bladder, no pelvic fins and a reduced, cartilaginous skeleton. 
The clavus is made up of fin rays and musculature from the dorsal and anal fins. The vertebral column is very reduced, and ribs are absent. 
Although the sunfish body is very rigid and rather inflexible, the large dorsal and anal fins are very powerful.

Family Size

To 3 metres in length and 4.2 metres in height from tip of dorsal fin to tip of anal fin.

Family Feeding

Ocean sunfishes are carnivores, feeding mostly on soft invertebrates such as jellyfishes, comb jellies and salps, they also feed on small crustaceans, squids and fishes.

Family Reproduction

Very little is known of the biology of ocean sunfishes. The sexes are separate and fertilisation is external. Although some spawning areas have been identified and females may produce up to 300 million tiny pelagic eggs, larvae are rarely collected.

Ocean sunfishes swim by synchronously flapping their dorsal and anal fins, using them like a pair of wings to glide through the water. This mode of swimming is thought to be very efficient, allowing oncean sunfishes to dive to repeatedly dive to remarkable depths.

Family Commercial

Ocean sunfishes are frequently taken in extraordinary numbers as bycatch in gillnet, driftnet and longline fisheries. For example, the South African longline fishery catches approximately 350,000 Mola mola annually. 
They are also taken as bycatch in midwater trawl fisheries. Although not targeted, some fisheries catch more Mola mola that the target species. 
Molids are highly valued as food fish throughout Asia and the largest markets are in Japan and Taiwan. They are also used in the traditional medicine industry. 
The marketing and sale of fish and fishery products derived from ocean sunfishes is banned in the European Union.

Family Conservation

No fishery anywhere in the world regulates the targeting or incidental bycatch of ocean sunfishes. They may also be 'finned' in some parts of the world, and may be threatened by floating debris such as plastic bags.

Family Remarks

The family name Molidae, is from the Latin mola meaning "millstone", suggesting the ocean sunfish resembles a millstone because of the rounded body shape, rough texture of the skin and its grey colour. 
The fossil record for the family dates back to the Eocene.

Author

Dianne J. Bray

References


Bass, A.L., Dewar, H., Thys, T., Streelman, J.T., Karl, S.A. 2005. Evolutionary divergence among lineages of the ocean sunfish family, Molidae (Tetraodontiformes). Marine Biology 148(2): 405-414.

Bray, D.J. 2008. Molidae, pp. 859-861. In Gomon, M.F., D.J. Bray & R.H. Kuiter (eds.) The Fishes of Australia's Southern Coast. New Holland Publishers, Chatswood, Australlia.

Britz, R., G.D. Johnson. 2005. Occipito-vertebral fusion in ocean sunfishes (Teleostei: Tetraodontiformes: Molidae) and its phylogenetic implications.Journal of Morphology 266: 74–79.

Fraser-Bruner, A. 1951. The ocean sunfishes (Family Molidae). Bulletin of the British Museum of Natural History 1: 89-121.

Gill, T.N. 1897. The distinctive characters of the Molinae and Ranzaniinae. Science 156: 966–967

Hutchins, J.B. 2001. Molidae. pp. 3966-3968 in Carpenter, K.E. & V.H. Niem (eds). The Living Marine Resources of the Western Central Pacific. FAO Species Identification Guide for Fisheries Purposes. Rome : FAO Vol. 6 pp. 3381-4218.

Johnson, G.D. & Britz, R. 2005. Leis' conundrum: Homology of the clavus of the ocean sunfishes. 2. Ontogeny of the median fins and axial skeleton of Ranzania laevis (Teleostei, Tetraodontiformes, Molidae). Journal of Morphology 266(1): 11-21.

Leis J.M. 1977. Development of the eggs and larvae of the slender mola, Ranzania laevis (Pisces, Molidae). Bulletin of Marine Science. 27(3): 448-466.

Matsuura, K. 2014. Taxonomy and systematics of tetraodontiform fishes: a review focusing primarily on progress in the period 1980 to 2014. Review for IPFC9 Special Issue. Ichthyological Research 62(1): 72-113. Open access DOI:10.1007/s10228-014-0444-5

Matsuura, K. & J.C. Tyler. 1994. Triggerfishes and their allies. In Paxton, J.R. & W.N. Eschmeyer (Eds). Encyclopedia of Fishes. Sydney: New South Wales University Press; San Diego: Academic Press.

Nelson, J.S. 2006. Fishes of the World. Hoboken, New Jersey : John Wiley & Sons, Inc. 601 pp.

Petersen, S. 2005. Initial bycatch assessment: South Africa's domestic longline fishery, 2000-2003. Domestic pelagic longline fishery: Bycatch Report 2000-2003. BirdLife South Africa, 45 pp.

Santini, F. & J.C. Tyler. 2002. Phylogeny of the ocean sunfishes (Molidae, Tetraodontiformes), a highly derived group of teleost fishes. Italian Journal of Zoology 69: 37-43.

Tyler, J.C. 1980. Osteology, phylogeny, and higher classification of the fishes of the order Plectognathi (Tetraodontiformes). National Marine Fisheries Service (U.S.). Technical Report 434: 1-422 figs 1-326

Tyler, J.C. & N. Holcroft. 2007. Tetraodontiformes. triggerfishes, boxfishes, puffers (fugu), molas and allies. Version 19 February 2007. http://tolweb.org/Tetraodontiformes/52153/2007.02.19 in The Tree of Life Web Project, http://tolweb.org/

Thys, T. http://oceansunfish.org/

Watson W. 1996. Molidae. in The Early Stages of Fishes in the California Current Region, Pp. 1439-1441. Moser, H.G. (Ed.) CalCOFI Atlas No. 33.

Winterbottom, R. 1974. The familial phylogeny of the Tetraodontiformes (Acanthopterygii : Pisces) as evidenced by their comparative myology. Smithsonian Contributions to Zoology 155: 1-102 figs 1-185.

Yanamoue, Y., Miya, M., Matsuura, K., Katoh, M., Sakai, H. & Nishida, M. 2004. Mitochondrial genomes and phylogeny of the ocean sunfishes (Tetraodontiformes: Molidae). Ichthyological Research 51(3): 269-273 fig. 1