Here's why:
* Physiological adaptations: Bull sharks have specialized kidneys that allow them to regulate the salt content in their blood, even in low-salinity water.
* Wide range: They can be found in rivers, estuaries, and coastal areas throughout the world, including the Amazon River and the Mississippi River.
* Reproduction: Some bull sharks have even been known to reproduce in freshwater environments, further highlighting their adaptability.
However, it's important to note that while bull sharks can survive in freshwater, they prefer saltwater. They spend a significant portion of their lives in the ocean and their young are typically born in saltwater environments.
Therefore, while bull sharks can live in freshwater, they are not solely freshwater creatures. They are euryhaline which means they can adapt to a wide range of salinities.