The bull shark (Carcharhinus leucas) is a species of shark that can live in both saltwater and freshwater. It is found worldwide in warm, shallow waters along coasts and in rivers. It is known for its aggressive nature and ability to adapt to different environments. But how does the bull shark manage to survive in such diverse habitats? And what are the benefits and costs of its freshwater adaptation?
The bull shark has a special organ called the rectal gland, which helps it regulate the salt concentration in its body. This allows it to adapt to different salinities. “Bull sharks are the only shark species that can survive in both saltwater and freshwater, and one of the few that can be found in rivers and lakes,” according to Wikipedia. The rectal gland is controlled by hormones that respond to changes in the water’s salinity. When the bull shark enters freshwater, the rectal gland stops secreting salt and the kidneys start excreting more urine. When the bull shark returns to saltwater, the opposite happens.
The bull shark has been reported to travel up the Mississippi River as far as Alton, Illinois, about 1,100 kilometers (700 miles) from the ocean. It has also been found in other rivers around the world, such as the Zambezi, the Ganges, and the Amazon. “The bull shark’s ability to live in freshwater is not just a curiosity, it is also a survival strategy. By moving into rivers, the bull shark can avoid competition and predation from other marine species, and access new food sources and breeding grounds,” Forbes reported.
The bull shark can reproduce in freshwater, and some populations may spend their entire lives in rivers without returning to the sea. “The Bull Shark’s Amazing Freshwater Survival Skills,” Humans for Survival wrote. However, the bull shark’s freshwater adaptation is not without costs. It requires a lot of energy and resources to maintain the salt balance in its body, and it exposes the shark to more parasites and diseases. It also increases the risk of human-shark interactions, which can have negative consequences for both parties. “The bull shark is one of the most dangerous sharks to humans, as it often attacks in murky water and near populated areas,” Wikipedia stated.
The bull shark is a fascinating and formidable animal that deserves respect and conservation. It is also a reminder of the amazing diversity and adaptability of life on Earth. “The bull shark is a master of adaptation. It can adjust its physiology to cope with changes in salinity, temperature, and oxygen levels. It can also tolerate high levels of pollutants and pathogens in the water,” Dutch Shark Society explained. The bull shark is a living example of how nature can overcome challenges and thrive in different environments.
– Bull shark – Wikipedia, Wikipedia, November 1, 2023
– Bull Sharks’ Remarkable Adaptation To Landlocked Life Revealed, Forbes, September 6, 2023
– The Bull Shark’s Amazing Freshwater Survival Skills, Humans for Survival, September 30, 2022
– Can Bull Sharks Live in Freshwater?, Dutch Shark Society, October 4, 2022