The Bull Shark

The bull shark is, without a doubt, the most dangerous shark to humans. They are the most aggressive shark known to mankind as they have been known to kill a wading animal or human on sight, even if they won't eat the body afterwards, without provocation.
Despite the vicious, menacing atmosphere that surrounds this species, they are truly one of the most fascinating branches of the family of sharks. This comes down to being one of the only two sharks that can survive in rivers as well as the oceans and seas of the world. For a long time, it was known as the only shark which could survive in both of these completely different conditions until a fisherman in Australia caught a speartooth shark which, due to the fact they had been thought extinct for 108 years, was met with great fanfare. Most sharks explode if they enter a river due to the lack of salt in the water, yet the bull shark, and its talent-sharing Australian counterpart, do not. Scientists remain unable to figure out how they do this.
Bull sharks can grow up to 2.4 metres long and can weigh up to 98 kilograms. They spend most of their  lives at depths of about 30 metres below the surface when they are not in rivers. They live in the Pacific, Atlantic and Indian oceans and can venture up to 2,500 miles up the Amazon river and have also been found in the Mississippi, Ganges and Zambezi rivers but the distance between them and the ocean in the last three rivers mentioned has never been measured.

A bull shark stalking the river bed of the Amazon surrounded by baby bait fish which
are too small for it to eat.