A river shark, as far as anyone knows, is a kind of shark that lives in freshwater rivers. All six known species of river shark belong to the Glyphis genus, which is part of the Carcharhinidae family. River sharks remain one of the great mysteries of nature; only a handful of river sharks have ever been captured, and few have ever been observed in their natural habitat. Scientists presume that, due to rare sightings, most river shark species are likely endangered.
As members of the Carcharhinidae family, river sharks share many of the same features of their ocean relatives. They have small, beady eyes, and their upper set of teeth is wide and serrated. Their nose is short and rounded, with nostrils spread wide apart. They also have a prominent dorsal fin. They bear the most resemblance to whaler sharks, which belong to the genus Carcharhinus. Whaler sharks have a lower set of teeth that protrude even when the jaw is closed, and they have a second dorsal fin which is roughly half the size of the other dorsal fin.
In all, there are six documented species of the Glyphis genus: Glyphis gangeticus, better known as the Ganges shark; Glyphis glyphis, known as the Speartooth shark; Glyphis siamensis, known as the Irrawady River Shark; Glyphis species A; Glyphis species B, also known as the Borneo River Shark; and Glyphis species C. The Ganges and the Irrawady sharks are named for the rivers in which they've been documented. The Glyphis river shark species have been documented in multiple rivers around Australia.
Very little is known about the ecology and habits of river sharks, due to rare sightings and scarce documentation. It's presumed that river sharks are primarily fish-eaters, although that's not known for certain. Nothing substantial is known about their breeding habits.
Sightings are so few and far between that at one point the Ganges shark wasn't sighted for roughly a century. Officially documented sightings of the Speartooth Shark are even rarer. River shark species are considered endangered, and some, such as the Speartooth and Irawaddy, possibly extinct—although it's very likely that such sharks may have been seen but mistaken for other river shark species.
The bull shark—also of the Carcharhinidae family—is sometimes confused for a river shark. Bull sharks have been known to swim for miles up freshwater streams, where they can live for years. The bull shark's main habitat and only breeding ground, however, is in the ocean.