The internal fluids of a shark have a salinity close to that of seawater. Sharks have many rows of teeth, and if one is lost, another is available to replace it. Sharks stop growing when they reach puberty.
Some species of shark prefer the taste of tuna to that of other fish.
You could be attacked by a shark if you went swimming in Lake Ontario in water less than four feet deep. The Basking Shark is the largest animal that has ever lived. The Thresher Shark uses its tail to herd fish into ever-smaller circles to facilitate feeding. Great Whites will attack boats and people. Bony marine fish uptake oxygen and loose carbon dioxide and salt through their gills.