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Characteristics, distribution and ecology
Taxonomische classification
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Author: (Norman, 1939)

Field Marks:
A houndshark with a moderately long snout and long gill area, first dorsal small and with its origin far anterior, over the pectoral bases, lateral eyes with the subocular ridges obsolete, and ventral caudal lobe hardly developed.

Diagnostic Features:
Snout rather short and moderately broad, preoral length about 0.7 to 0.9 times mouth width; gill region greatly expanded, distance from spiracle to 5th gill slit greater than prespiracular head; width of longest gill slits nearly equal to eye length; labial furrows shorter, uppers falling well behind level of lower symphysis. Ventral caudal lobe hardly expanded in adults. Colour brownish or greyish above and lighter below, with no conspicuous markings; margins of dorsal fins often somewhat darker.

Geographical Distribution:
Red Sea and Gulf of Oman to Pakistan and southwestern India. A low-finned, somewhat short-headed Iago is largely sympatric with I. omanensis at least off southwestern India, and in the Bay of Bengal there is a possibly dwarf, omanensis-like Iago that may or may not be distinct.

Habitat and Biology:
A small, deepwater tropical shark of the continental shelf and slope from 110 m or less depth to at least 1000 m depth and possibly down to 2195 m in the Red Sea, on or near the bottom. This species has been reaularly caught in warm water with oxygen levels often at a low level, at 16 to 25 C and 0.2 to 2.4 ml/l oxygen (mostly at 0.2 to 0.6 ml/l). Compared to I. garricki and the Philippine Iago, this species has an enlarged branchial region, with larger gill slits and expanded branchial septa with much greater expanses of gill lamellae; these are apparently adaptations for living in warm, relatively anoxic, and probably (especially in the Red Sea) hypersaline waters.

Viviparous, with a yolk-sac placenta; litter size probably about 2 to 10 young.

Definitely known to eat bony fishes and cephalopods. Nair and Appukuttan (1973) note that bony fishes, particularly lanternfishes, were the most important food item of this species off southern India, followed by deepwater squid, crustaceans (shrimo and larvae of mantis shrimp). bivalves and gastropods; sea grass and mud were found in a few stomachs. It is probable, however, that at least some of the Iago examined by these writers were not I. omanensis but its low-finned sympatriot (K.K. Appukuttan, pers.comm.).

Maximum size 58 cm; adult males 30 to 37 cm, adult females 40 to 58 cm. Sexual dimorphism in size in this species is considerable, with the largest males about 63% as long as the longest female (37 versus 58 cm) and weighing about 1/6 as much (Compagno and Springer, 1971); size at birth at least 17 cm (A. Baranes, pers.comm., term fetuses).

Interest to Fisheries:
Limited, taken in gillnet fisheries in southern India and also caught by handline fisheries in Israel in the Gulf of Agaba (Elat). In India, utilized fresh for human consumption.

Type material:
Holotype: British Museum (Natural History), BMNH 1939.5.24.9, 280 mm immature female. Type Locality: Gulf of Oman, 210 m depth.

Bigeye houndshark (Iago omanensis)