Is there really such a thing as a fresh water bull shark? When we think of sharks we usually think of them as ocean dwellers. However, there are a few species of sharks that have the ability to survive in fresh water for extended periods of time.
The bull shark (Carcharhinus leucas), is a prime example of a saltwater shark that has the ability to venture into freshwater territory. The bull shark has been known to live in fresh water estuaries, rivers, and lakes. According to aquaticcommunity.com, the bull shark has been found up to 2600 miles upstream in freshwater rivers such as the Amazon (the largest river in the world by volume located in South America). It is also a well known fact that the bull shark lives in Lake Nicaragua (the largest fresh water lake in Central America).
When first discovered, it was unknown to researchers how the bull shark was able to survive in fresh water, because the bull shark has a higher salinity level in its body than the water surrounding them, this is true for ocean water as well. It is now known that the bull shark has a special ability to adapt the process of osmoregulation to survive in a wide range of water salinities. Both salt water and fresh water fish use osmoregulation, and it is an ability that allows an organism to sustain a constant concentration of water in its body when its external environment would normally cause it to gain or lose too much water. Although osmoregulation makes the bull shark more adaptable to fresh water, their body still holds a greater salinity than the freshwater surrounding them. This leads to the bull shark absorbing more water than usual, and the excess fluid is dispelled through urination. The bull shark produces up to twenty times more urine in freshwater than they do and saltwater.
The bull shark has been known to survive in fresh water for up to six years, but just because the bull shark can live in fresh water for so long does not necessarily make it a freshwater shark. The bull shark is required to return to the oceans salt water to breed. A bull shark found living in fresh water has simply adapted to the fresh water environment,t but is still considered to be a salt water organism due to their need to travel into salt water for breeding purposes.
There is no such thing as a fresh water bull shark. Yes, it is true that a bull shark can survive in fresh water for long periods of time due to an ability to adapt the process of osmoregulation, but they are still considered to be a salt water species.
Sources:
http://www.aquaticcommunity.com/sharkfish/freshwatersharks.php
http://www.sharksavers.org/en/education/shark-biology-behavior/385-how-bull-sharks-can-live-in-fresh-water-through-clever-osmoregulation.html
