Are there any freshwater sharks?
Several species of sharks are known to live in freshwater environments, but whether they should be considered true freshwater fish is debatable. Probably the most mysterious are the river sharks of the genus Glyphis. Fewer than ten species have been identified in watercourses around southeast Asia and Australia, with some still waiting to be officially classified, and all are extremely rare.
Much better known is the bull shark. This worldwide species enters warm water estuaries from the ocean and then swims into fresher water upstream. If you see an adult bull shark from a kayak, you might wish you had a bigger boat, as they are large and aggressive predators and have been known to attack humans. A notable characteristic of bull sharks living in freshwater habitats is that they excrete a large amount of urine. Sharks that evolved in the ocean have a great deal of salt naturally present in their bodies to prevent them from losing water to the sea through osmosis. In the non-saline
