The bull shark, Carcharhinus leucas, also known as the Zambezi shark or unofficially Zambi in Africa and Nicaragua shark in Nicaragua, is a shark commonly found worldwide in warm, shallow waters along coasts and in rivers. The bull shark is known for its aggressive nature, predilection for warm shallow water, and presence in brackish and freshwater systems including estuaries and rivers.
The bull shark can thrive in both saltwater and freshwater and can travel far up rivers. They have even been known to travel as far up as Kentucky in the Ohio River, although there have been few recorded freshwater attacks. They are probably responsible for the majority of near-shore shark attacks, including many attacks attributed to other species. Bull sharks are not actually true freshwater sharks, despite their ability to survive in freshwater habitats (unlike the river sharks of the genus Glyphis).
Commentary paraphrased from Scientific American's Myth Busting Article on Bull Shark Testosterone.
Researcher Neil Hammerschlag told news outlets that bull sharks “have the most testosterone of any animal on the planet". However it's the Grand Theft Auto 4 character Bruce Kibbutz who, during the game, mentions how he "juices" on testosterone taken from Chilean bull sharks. As would naturally follow in our consumer mentality, people [primarily body builders] want to know, can you really bulk up muscle mass on bull shark testosterone better than steroids?
That we do not know.