What Makes a Fish Move in Swimming?
This is a puzzling question, I am sure. Of course, you at once cause several other questions as soon as you ask this one such as the following: Does the water in front of him move out of the way and then close in behind him? If so, where does it go in the meantime? Does the fish move the water forward or up or down or what does he do?
The answer is, of course, in the movements of the fish’s tail. The fish in swimming is surrounded with water, top, bottom and all sides of him. The pressure of the water on the fish is the same at all points so that any motion made by him would have a tendency to make him move. As a matter of fact the tail in moving from side to side creates a current in the water from the head to the tail, or rather would produce an actual current if the fish remained perfectly still. Instead of making an actual current of water, the body of the fish is moved forward.
As to whether the water ahead of him opens up first and then the water behind him is a more difficult question to answer. To the appearance it would seem as if the water moved at both ends and sides at once, but according to scientific theory, the water at the head of the fish is displaced first.