Sharptail mola

Sharptail mola
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Tetraodontiformes
Family:	Molidae
Genus:	Masturus
Species:	M. lanceolatus
Binomial name
Masturus lanceolatus (Liénard, 1840)
Synonyms
Orthagoriscus lanceolatus Liénard, 1840 Pseudomola lassarati Cadenat, 1959

The sharptail mola, Masturus lanceolatus, is a species of mola found circumglobally in tropical and temperate waters. It is similar in appearance to the ocean sunfish (Mola mola), but can be distinguished by the projection on its clavus (pseudo-tail). Other common names include sharpfin sunfish, point-tailed sunfish, and trunkfish.^[1][2] Rarely encountered, very little is known of the biology or life history of the sharptail mola. It has recently become important to commercial fisheries operating off eastern Taiwan.^[3]

Distribution and habitat

The distribution of this sharptail mola is worldwide in tropical and temperate waters.^[1] They are primarily inhabitants of the epipelagic zone but are rarely sighted at the surface, many of those appearing to be ill and parasite-ridden. During the day, they spend most of their time at a depth of 5–200 meters (16–660 ft), preferring water temperatures above 20°C but making repeated dives into cooler, deeper water, possibly to feed or to avoid predators. At night, they spend most of their time between 100–250 meters (330–820 ft). They have been sighted in the mesopelagic zone to a depth of 670 meters (2,200 ft), but may descend to over 1,000 meters (3,280 ft). One tagged individual in the Gulf of Mexico moved an average of 10 km (6 mi) a day.^[4][5]

Description

One of the largest bony fishes, the sharptail mola can measure up to 3.4 meters (11 ft) long and weigh 2,000 kg (4,410 lbs).^[1] It has an oval body with an evenly convex forehead profile. The eyes are placed more forward on the head than in the genus Mola. The teeth in both jaws are fused into beak-like plates. The dorsal and anal fins are placed posteriorly, and the base of the dorsal fin is longer than that of the anal fin. In place of a caudal fin, the dorsal and anal fins merge into a clavus, formed by 18-20 fin rays. The central rays in the clavus are supported by the last vertebra and form an elongated triangular lobe; some authors believe these rays to be remnants of the larval caudal fin, though this is disputed.^[2][6][7]

The skin is covered with small dermal denticles that are finer than those of the ocean sunfish. The coloration is silvery with the upper parts of the sides grayish brown to blackish. The sides may bear ill-defined dark spots. The dorsal and anal fins are slaty, while the clavus may have pale blotches.^[8] This species is distinguished from the similar Masturus oxyuropterus by its prominent chin, the lack of a concavity above the eyes, and the unequal lengths of the dorsal and anal fin bases. Fraser-Brunner proposed that these two forms may represent different sexes of the same species.^[7]

Biology and ecology

Sharptail mola near the surface.

Robert Collett, who examined some of the first known specimens of sharptail mola, speculated that they might represent abnormal ocean sunfishes that had retained larval characteristics. However, it is now known that the caudal projection is a secondary development that follows the loss of the primary tail.^[9] The swimming mode of the sharptail is similar to that of other ocean sunfishes, using sculling motions of its long dorsal and anal fins to propel itself through the water. The anal fin moves more extensively than the dorsal fin. The small pectoral fins move constantly to control pitch, while the clavus is employed as a rudder.^[4]

Juvenile sharptail molas are known to feed on benthic annelids and sponges. Adults likely feed on medusae, siphonophores, ctenophores, and salps, as well as some fishes, crustaceans, and molluscs.^[4] Sharptail molas sometimes have remoras attached to the surface of their bodies or inside the buccal cavity. In 1949, a sharptail mola off North Carolina was found with a common remora (Remora remora) wedged inside the gill arches on its right side. This evidently impaired the respiration of the mola, such that it foundered on the beach and was collected by fishermen.^[10]

Molas are oviparous and are amongst the most fecund of all fishes. Larval sharptail molas are rounded in shape and develop large pyramidal dermal spines over the body, which persist through a prejuvenile phase called the "Molacanthus" stage. In this stage, the body is deep and compressed, with a thin keel-like structure below the abdominal region. This ridge is made from skin and covered with several rows of small spines. The skin is rough, being covered with small prickles. The spines eventually diminish in size and disappear, leaving scars obvious on the sides of young fish up to 70 mm (2.8 in) long. Their coloration is dark brown on the back, becoming very light on the sides and belly.^[11][12] The lifespan for this species is estimated to be 85 years for males and 105 years for females.^[3]

Relationship to humans

Since 2002, promotion of an ocean sunfish festival in Hualien County, Taiwan has increased demand for the meat of the sunfish (called "mambo fish" after a public vote), whereas before only the intestines and reproductive organs were sold while the rest of the fish was discarded. The month-long April festival draws some 120,000 visitors and features "101 ways to eat" sunfish. Consequently, catches of sunfishes off eastern Taiwan have risen sharply, with the sharptail mola comprising 90% of the catch. In 2005, 208 tonnes were landed and the annual sunfish catch was valued at one million USD. The species is caught by set net, drift net, and longline fisheries. The impact of this increased exploitation on sunfish stocks is under investigation.^[3][13][14]

References

1. ^ ^{a b c} Froese, Rainer, and Daniel Pauly, eds. (2009). "Masturus lanceolatus" in FishBase. March 2009 version.
2. ^ ^{a b} McGrouther, M. (2007). Sharptail Sunfish, Masturus lanceolatus. Australian Museum Fish Site. Retrieved on March 5, 2009.
3. ^ ^{a b c} Liu, K.M., Lee, M.L., Joung, S.J. and Chang, Y.C. (Jan. 14, 2009). "Age and growth estimates of the sharptail mola, Masturus lanceolatus, in waters of eastern Taiwan". Fisheries Research 95 (2-3): 154–160. doi:10.1016/j.fishres.2008.08.013. 
4. ^ ^{a b c} Harbison, G.R. and Janssen, J. (May 13, 1987). "Encounters with a Swordfish (Xiphias gladius) and Sharptail Mola (Masturus lanceolatus) at Depths Greater Than 600 Meters". Copeia (American Society of Ichthyologists and Herpetologists) 1987 (2): 511–513. doi:10.2307/1445796. JSTOR 1445796. 
5. ^ Seitz, A.C., Weng, K.C., Boustany, A.M. and Block, B.A. (2002). "Behaviour of a sharptail mola in the Gulf of Mexico". Journal of Fish Biology 60: 1597–1602. doi:10.1111/j.1095-8649.2002.tb02452.x. 
6. ^ Proceedings of The Academy of Natural Sciences (Vol. 122). Academy of Natural Sciences. 1970. ISBN 1437955193. 
7. ^ ^{a b} Weber, M. and de Beaufort, L.F. (1911). The fishes of the Indo-Australian Archipelago XI. Brill Archive. 
8. ^ Bigelow, H.B. and Schroeder, W.C. (1953). Sharp-tailed sunfish. Fishes of the Gulf of Maine. Retrieved on March 5, 2009.
9. ^ Hubbs, C.L. and Giovannoli, L. (Oct. 30, 1931). "Records of the Rare Sunfish Masturus lanceolatus for Japan and Florida". Copeia (American Society of Ichthyologists and Herpetologists) 1931 (3): 135–137. doi:10.2307/1437338. JSTOR 1437338. 
10. ^ Funderburg, J.B. and Eaton, T.H. (Jr.) (Sep. 26, 1952). "A New Record of the Pointed-Tailed Ocean Sunfish, Masturus lanceolatus, from North Carolina". Copeia (American Society of Ichthyologists and Herpetologists) 1952 (3): 200. doi:10.2307/1439726. JSTOR 1439726. 
11. ^ Richards, W.J. (2006). Early stages of Atlantic fishes: an identification guide for the western central North Atlantic. CRC Press. ISBN 0849319161. 
12. ^ Gudger, E.W. (Apr. 10, 1935). "Some Undescribed Young of the Pointed-Tailed Ocean Sunfish, Masturus lanceolatus". Copeia (American Society of Ichthyologists and Herpetologists) 1935 (1): 35–38. doi:10.2307/1436634. JSTOR 1436634. 
13. ^ Chung, L. (Jun. 11, 2004). "Seafood festivals draw tourists but empty seas". The Straits Times, Singapore Press Holdings Ltd.
14. ^ Ferguson, C. (Feb. 15, 2009). Taiwan Delicacies - Mambo Fish CraigFergusonImages. Retrieved on March 6, 2009.