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The speartooth shark ( Glyphis glyphis) is a rare species of river shark, belonging to the family Requiem shark. It inhabits coastal marine waters and tide reaches of large tropical rivers in northern Australia and New Guinea. Despite being a member of the river shark genus, it is also found in near-shore marine waters, favoring highly turbid environments over a wide range of salinity. This robustly built, gray-colored shark is characterized by a short and broad snout, tiny eyes, a relatively large second dorsal fin, and a black blotch beneath each pectoral fin near the tip. Another identifying trait is its teeth, which are large, triangular, and serrated in the upper jaw and narrow, spear-like, and serrated only near the tips in the lower jaw. Adults grow to about long.
Preying on demersal and , the speartooth shark is adapted for hunting in near-complete darkness. It is not as active as other , moving upstream and downstream with tide currents so as to save energy. Reproduction is viviparous, with females forming a connection to their young, though details are unknown. The speartooth shark is threatened by bycatch in commercial and recreational fisheries, as well as by habitat degradation. Given its small population, restricted range, and stringent habitat requirements, this species is highly susceptible to these pressures and has been listed as vulnerable by the International Union for Conservation of Nature.
Müller and Henle's type specimen remained the sole known record of the speartooth shark until specimens of the "Bizant river shark" ( Glyphis sp. A) were caught in Australia in 1982. Subsequently, work by Leonard Compagno, William White, and Peter Last confirmed initial suspicions that "sp. A" was the same species as G. glyphis. Thus, in Australia, this shark may also be referred to as the Bizant river shark or the Queensland river shark.
Fossil teeth suggest that the speartooth shark once had a much larger range, with fossils being known from the Early Miocene to Pliocene of Portugal and the Pliocene of Italy. Potential records of this species are also known from the Late Miocene of Brunei.
Newborn to subadult speartooth sharks exclusively inhabit areas with fast tide currents and muddy bottoms; the flowing water produces heavy turbidity, such as that <1% of sunlight penetrates beyond a depth of . The salinity level of these waters range from nearly fresh water (0.8 ppt) to nearly Seawater (28 ppt), and temperatures range from . Younger sharks are generally found further upstream than older ones. A study that tracked three individuals in the Adelaide River reported that they moved upstream with the flooding tide and downstream with the ebbing tide, averaging each way. The average swimming depth was determined for one individual to be , in the middle of the water column. Adults were entirely unknown until 2014, when three specimens (two males and one female) were documented by scientists visiting fishing villages on Daru island, Papua New Guinea. All three were caught in coastal waters off the island. No evidence exists of segregation by sex.
Recently in 2024 a new population where found in the Roper River of the Northern Territory, the first time ever documented living in that area, there was enough living specimens for a viable population and keeping the species alive.
The large have strongly convex leading and concave trailing margins, and blunt tips. The are triangular with nearly straight margins. The first dorsal fin originates over the pectoral fin insertions, and is broadly triangular with a narrow apex and a concave trailing margin. The second dorsal fin measures about 67–77% as tall as the first and is similar in shape; there is no midline ridge between the dorsal fins. The anal fin is almost as large as the second dorsal fin and lies slightly behind; it has a deep notch in the posterior margin. The caudal fin is asymmetrical; the lower lobe is narrow and well-developed, while the upper lobe has a gently convex upper margin and a prominent notch in the ventral margin near the tip. The body is covered by small, overlapping oval-shaped bearing three or five horizontal ridges leading to marginal teeth. This species is plain slate-gray above, including the upper surfaces of the pectoral and pelvic fins, and the caudal fin; the underside is white. The boundary between dark and light runs through the bottom rim of the eye, through the gill slits, over the flank well above the pelvic fins, and onto the upper caudal fin lobe. The fins darken towards the posterior margins, forming a black edge on the upper caudal fin lobe; each pectoral fin also has a black blotch underneath, near the tip. The eyes are ringed in white.
The range of conservation threats faced by the speartooth shark, coupled with its small population and restricted range and habitat preferences, have led the International Union for Conservation of Nature to assess it as vulnerable. Furthermore, in Australia, it has been listed as critically endangered on the 1999 Commonwealth Environment Protection and Biodiversity Conservation Act. The speartooth shark is within the scope of the Sawfish and river shark multispecies recovery plan made under the EPBC Act. It has also been listed as vulnerable on the 2000 Territory Parks and Wildlife Conservation Act, though a management plan has yet to be enacted. Sharks in the Kakadu and Rinyirru National Parks are protected somewhat from habitat alteration, if not fishing. No regulations restrict the capture of this species in Papua New Guinea.
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