Sharks do not have a swim bladder like fish, they use bile to control their depth. Evidentially sharks don't have bones or overlapping scales either. The sharks in my tank are not really sharks they are just fish that look kind of like sharks.
OK now back to fish. Fish live in fresh water, salt water, and brackish water. Fresh water is water that does not have salt in it, it is found in rivers, lakes, and ponds and so are fish. Salt water is water with lots of salt in it and is found in the Oceans, and two lakes the Dead Sea and the Great Salt Lake. Fish live in the oceans but not in salty lakes. Brackish water is water that is salty but not as salty as the oceans, brackish water is found in estuaries where rivers meet the ocean. Different types of fish live in fresh water, brackish water, and salt water.
For the most part fresh water fish can't live in salt water and salt water fish can't live in fresh water. Though there are exceptions like Salmon that live in the ocean except for when the are going to reproduce when they swim up the rivers to lay their eggs. Another exception is the Sea Cat, also called the Silver Tipped Sharks, and some other names I cannot remember. The Sea Cat is born in fresh water river and as they grow the move closer to the ocean. So one way to look at it is that the bigger they get the saltier they like the water.
