Most sharks cannot survive in freshwater for long. Because of osmotic pressure, their kidneys would burst if they remained in freshwater, which has a lower salt content than seawater. Even though they may be able to live in freshwater, they will not thrive like they do in salt water.

Sharks usually do not have any natural predators, but sometimes, smaller shark species are preyed upon by orcas and large sharks. In some instances, sharks are also attacked by dolphins. Sharks, in turn, prey on invertebrates, fishes, smaller sharks, and penguins. Some sharks also prefer eating plankton, algae, and other plant-based food items. 

Sharks have eye anatomy comparable to that of humans, and they have excellent vision. However, their ability to see objects is contingent on several conditions. Sharks, for example, have better eyesight in low light. They can also adjust their field of vision as needed.

Sharks, like human beings and other mammals, have eyelids. However, some shark species have three eyelids, which makes them different from humans. This third eyelid acts as a protector against potential abrasions and also keeps the shark’s eyes moist.

Sharks do not have swim bladders. Although, majorly all fish typically have a swim bladder, which is an internal gas-filled organ that helps them control their buoyancy and maintain a certain depth in the water. Sharks don’t need this because they are naturally buoyant and their skeletons don’t contain the hollow spaces that are necessary to accommodate gas-filled organs such as the swim bladder.

Sharks have gills, like most aquatic creatures. It helps the sharks derive oxygen from the water that passes over the gills and is then absorbed by small capillaries before being pumped through the rest of the body. In addition, gills help the sharks breathe out carbon dioxide from the body. 

It’s not uncommon for sharks to lose their teeth in a fight, so they can quickly replace them. While most species of shark have between 3 and 10 rows of replacement teeth, bull sharks can have over 20 rows! This means they can replace more than 30,000 teeth in their lifetime.

Sharks neither like nor dislike humans. They are quite indifferent to human presence since human beings are not a part of their natural diet. However, if they feel threatened, sharks may sometimes bite you. Although most shark attacks on humans are provoked, there have also been recorded instances of unprovoked attacks.

Shark teeth are not made of bones but cartilage. Shark teeth, in particular, are formed of hardened tissue called dentin. Dentin is what allows shark teeth to fossilize quickly.

You can pet a shark by using two fingers and being gentle with them. However, you need to be careful around them and opt for professional assistance if needed. Sharks can get quite aggressive if they feel threatened by you, and therefore, it is important to make them feel safe so that they come to you.