The Bigeye Thresher (Alopias superciliosus) is a species of thresher shark, family Alopiidae. This shark is caught by commercial fisheries across its range; the meat is not highly regarded but the skin, fins, and liver oil are valued. It has been assessed as Vulnerable by the International Union for Conservation of Nature (IUCN).
The eyes of the bigeye thresher can measure up to 10 cm (3.9 in) across in adults. Each eye is taller than wide, with a bulbous upper portion. The orbits extend onto the dorsal surface of the head, allowing the eyes to orient upwards. There are also a pair of distinctive lateral grooves that extend from above the eyes to over the gill slits, giving it a "helmet"-like appearance. The snout is moderately long and bulbous, and there are no labial furrows at the corners of the mouth. The teeth are moderately large with a single, narrow cusp. There are 19–24 teeth in the upper jaw and 20–24 teeth in the lower jaw; their shapes are similar in both jaws. There are large and small? dermal denticles, with the smaller ones more numerous and interspersed amongst the larger ones. The smaller denticles taper to a point.
Up to half the body length is taken up by the long upper lobe of the caudal fin, which is broader than in other threshers. The large pectoral fins have a curved anterior margin and broad tips. The first dorsal fin is placed further back than in the other thresher sharks, with the free rear tip located above or just before the pelvic fins. Its coloration is a deep, metallic violet to purplish brown above and creamy white below. This color rapidly fades to a dull gray after death. Most bigeye threshers are 3.3–4.0 m (11–13 ft) long and weigh 160 kg (350 lb).
Bigeye threshers are usually found over the continental shelf and in the? open sea, though they are occasionally encountered in shallow coastal waters. They occur in surface temperatures of 16–25 °C (61–77 °F), but have been tracked as far down as 723 m (2,372 ft), where the temperature is only 5 °C (41 °F).
The bigeye thresher has larger teeth than other threshers and feeds on a wider variety of prey. Known food items include schooling forage fish such as mackerel and herring, benthic fishes such as hake and whiting, larger pelagic fishes such as lancetfish and small? billfish, squid such as lycoteuthids and ommastrephids, and possibly crab megalopae.