|Northern River Shark|
CSIRO National Fish Collection
Most of the world’s shark species are found in the ocean, but there are some elusive and not so elusive sharks out there that live in freshwater. Granted, there are only two types and possibly only five or six species of freshwater sharks, but they do exist and at least one is quite dangerous.
Bull sharks are typically found in rivers or near warm shores in tropical areas. However, these animals are not strictly fresh water dwellers. Some of them spend all of their time in fresh water, while others swim to salt water for mating and birthing. They are able to transition between the two because they have the ability to control the amount of urea and sodium in their bodies. They also urinate frequently to rid themselves of excess fresh water.
Bull sharks are medium-sized sharks that are grey on their top half and white on the bottom. They have short, blunt noses that they use to head butt their prey before attacking. They weigh between 200 and 500 pounds and can be up to eight feet long. On average, they live about 16 years. Their diet consists of just about any meat that swims near them, so humans should be weary in areas where bull sharks have been sighted. Bull sharks are one of the three most dangerous shark species in the world.
River sharks are some of the most elusive and rare fish species on Earth. We don't know much about them. For the most part, their diet, mating habits, populations, behavior, life expectancy, specific locations and size are all mysteries. It is believed that they eat fish, though not enough research has been done on them to know for sure. They are also believed to spend their entire lives in rivers, making them the only true fresh water sharks in the world. To date, there are only around five known species, two of which may actually be one and the same. Of the five known species of river sharks, the speartooth river shark and the New Guinea river shark may be the same. The other three species include the Ganges river shark, which is critically endangered, the Bizant river shark and the Borneo river shark.
So you see, there are freshwater sharks in the world. In the case of the bull shark, we can only marvel at its adaptations and avoid its aggressive behavior. In the case of river sharks, we can only hope that we will be able to obtain more information about these creatures in the future.