How do fish float?
Many fish have an expandable sac (like a human lung), called swim bladder, that allows them to rise and sink in water. As the fish fill the bladder with air extracted from the surrounding water through their gills, they rise through the water. As they let the air out and deflate the bladder, they float lower down. How can seals stay long in icy waters? Seals are warm-blooded. This, and the thick layer of fat measuring to several inches beneath their skin, called blubber, insulate and help keep them warm in the coldest seas. Seals also have thick under and overcoats of fur, which they shed once a year, that protect their skin from icy waters. Why do sharks have to keep swimming? Sharks don’t have swim bladders, so they have to swim and propel themselves forward to ascend and descend in the water. As they swing their tail back and forth, they are propelled forward and water is pushed around their fins creating lift that pushes them upward (sharks also have large, fat-filled livers that g
