When we hear the term 'freshwater sharks', most of us are likely to assume that it refers to those species of sharks that live in freshwater sources, i.e., rivers. While that is true, at times, the term is also used for species of bony fish which are not related to sharks.
The list of true freshwater shark species include the bull shark and river shark, whereas other species, which are commonly referred to as small freshwater sharks, include species like the bala shark and roseline shark.
True Freshwater Sharks
This group includes two of the most popular members of the shark family, the bull shark (Carcharhinus leucas) and river shark (genus Glyphis). While the bull shark is found in tropical freshwater sources, river sharks are restricted to fresh and brackish water sources in Asia and Australia.
The bull shark is considered one of the most aggressive sharks in the world. An adult male can grow on to attain a length of 3 meters and weigh around 500 lbs. These sharks inhabit rivers and shallow parts of the ocean in the tropics, as a result of which their chances of coming in contact with humans are high.
Being apex predators in their natural habitat, these sharks feed on a wide range of marine lifeforms, including different types of fish, turtles, mollusks, etc. Their amazing ability to survive in saline and freshwater sources make them one of the most fascinating creatures of the marine biome.
Bull sharks are enlisted as 'Near Threatened' species by the International Union for Conservation of Nature (IUCN).
Basically, river shark is an umbrella term for five species of sharks belonging to the Glyphis genus, which are found in the rivers of Asia and Australia.
- Ganges shark (Glyphis gangeticus)
- Northern river shark (Glyphis garricki)
- Speartooth shark (Glyphis glyphis)
- Irrawaddy river shark (Glyphis siamensis)
- Borneo river shark (Glyphis sp. B)
While the Irrawaddy river shark, Northern river shark, and the Ganges shark are considered 'Critically Endangered' by the IUCN, the Speartooth shark is considered 'Endangered'. As for the Borneo river shark, it is yet to be described scientifically and most of the information available about it, is based on occasional sightings.
A large number of people actually mean freshwater cyprinids when they say freshwater sharks. Cyprinids are small bony fish which are quite popular in aquarium trade; courtesy, their colorful appearance and docile nature. These species are also referred to as 'sharkminnows' or simply 'sharks'.
Some of the most popular members of this family include the bala shark, Epalzeorhynchos, Labeo, roseline shark, etc.
Of late, the existence of freshwater sharks has become a subject of raging debate among marine biologists.
While several sources classify bull sharks and river sharks as freshwater species, others are of the opinion that these species are actually marine sharks which have the ability to travel upstream and survive in freshwater. That, however, doesn't change the fact that true sharks are different from freshwater cyprinids.