The Ganges shark (Glyphis gangeticus) resides in the rivers and estuaries of Bangladesh, which gives them their name. IUCN critically endangered or endangered marks all 5 other species within its genus, except the unevaluated Borneo river shark.
Only 3 museum specimens of the elusive Ganges shark exist, all from the 19th century. The last confirmed record of this shark was 52 miles upstream of the month of the Hooghli River in 2001.
The only known shark species to have euryhylaline adaptions are the bull shark and 5 species of river shark. Eurhylaline adaptations allow sharks to tolerate a wide range of salinities. Therefore, these sharks spend extended periods of time in freshwater environments as well as marine.
Sharks need to retain salt within their bodies to prevent cells from rupturing. In sharks, urea retention helps reduce the potential osmotic loss of water. Salt secretion by the rectal gland counteracts the influx of sodium and chloride across the gills and gut.
Sharks’ ability to tolerate freshwater is linked to salt retention, and the ability to adapt their process of regulating water. The kidneys in freshwater tolerant species remove less salt and more urea from the bloodstream when in freshwater. This kidney ability means they have to pee much more in freshwater environments.