Six-gill stingrays
| Six-gill stingrays | ||||||||||||
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Six-gill stingray ( Hexatrygon bickelli ) |
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| Systematics | ||||||||||||
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| Scientific name of the family | ||||||||||||
| Hexatrygonidae | ||||||||||||
| Heemstra & Smith , 1980 | ||||||||||||
| Scientific name of the genus | ||||||||||||
| Hexatrygon | ||||||||||||
| Heemstra & Smith, 1980 | ||||||||||||
| Scientific name of the species | ||||||||||||
| Hexatrygon bickelli | ||||||||||||
| Heemstra & Smith, 1980 |
The six-gill stingray ( Hexatrygon bickelli ) is a species of ray that was first described in 1980 and monotypically placed in its own genus and family. Further described species of the genus ( Hexatrematobatis longirostris Chu & Meng, 1981 , Hexatrygon brevirostra Shen, 1986 , H. taiwanensis Shen, 1986 , H. yangi Sheng & Liu, 1984 ) are probably only subspecies or local forms. The ray occurs in the Indian Ocean from the coast of South Africa via India to Indonesia and the west coast of Australia, as well as in the western and central Pacific from the South China Sea , Taiwan, Japan and the coast from Queensland to Hawaii.
features
The fish are the only species of ray with six gill slits. They are 48 to 50 cm in length at birth, reach sexual maturity with a length of 105 to 113 cm and the largest specimen measured so far, a fully grown female, was 168 cm in length. The rostrum is soft, very elongated and pointed. The nostrils are very large and are right in front of the mouth. The distance between the nostrils and the mouth is much smaller than the diameter of the nostrils. They are not connected to the mouth via pits. The front nasal curtain is very short. The mouth is almost straight, the jaw teeth are oval to round. 44 to 102 teeth were counted in both jaws, with adult animals having more teeth than young ones. The eyes are small and are clearly in front of the injection holes . The body disc is smooth with no denticles or thorns. The pelvic fins are short, rounded and have no division into anterior and posterior lobes. The tail is short and not whip-like. Its length is 0.5 to 0.7 times the length of the body disk. One dorsal fin is missing. Just behind the ventral fin are one or two spikes on the top of the tail. The caudal fin is approximately symmetrical and very long. Their length is about a third of the tail length. It does not resemble the tail fins of the shark, but more like a leaf. The turns of the spiral casing were counted in one specimen, there are 14 turns. In contrast to the other rays, which have a relatively complex brain, the brain of the six-gill stingray is relatively simple. On the upper side the animals are colored purple-brown, the belly side is whitish with smoky markings. The top and bottom of the tail are dark.
Way of life
The six-gill stingray lives on soft bottoms on the continental shelf at depths of 300 to 1120 meters. Some strandings, a possible catch by an angler and an observation of a food-seeking specimen by Japanese divers documented by photographs show that the species occasionally visits shallower areas (20 to 30 meters). The fish are viviparous but have no yolk sac placenta . Three to five young rays are born per litter. No further information is known about reproduction. When searching for food in the seabed, the fish use both the long, flexible snout and the strongly retractable mouth. One specimen examined by scientists had wounds caused by a cigar shark ( Isistius ). Six-gill stingrays are occasionally caught as bycatch , but only marketed in Taiwan.
literature
- Joseph S. Nelson : Fishes of the World. 4th edition. John Wiley & Sons, Hoboken NJ et al. 2006, ISBN 0-471-25031-7 .
Individual evidence
- ↑ Phillip C. Heemstra, Margaret Mary Smith: Hexatrygonidae, a new family of stingrays (Myliobatiformes: Batoidea) from South Africa, with comments on the classification of Batoid fishes. Ichthyological Bulletin of the JLB Smith Institute of Ichthyology; No. 43
- ^ David A. Ebert: Deep-sea Cartilaginous Fishes of the Indian Ocean. Volume 2 Batoids and Chimaeras . FAO Species Catalog for Fishery Purposes No. 8, Vol. 2, ISSN 1020-8682. Page 87-89.
Web links
- Hexatrygon bickelli on Fishbase.org (English)
- Hexatrygon bickelli inthe IUCN 2013 Red List of Threatened Species . Posted by: McCormack, C., Wang, Y., Ishihara, H., Fahmi, Manjaji, M., Capuli, E. & Orlov, A., 2007. Retrieved October 3, 2013.