fish biology - because there are no less than 8,000 kinds of freshwater fish , it is difficult to describe the "typical" fish. However , all fish have some common attributes. Since water is 800 times denser than air , fish have developed a variety of ways to move easily , breathe and feed in this dense medium. The biological adapatations that developed for life under water include the body shape , fins , scales and swim bladder.
fish evolution - the group of aquatic animals we call fish has evolved foe over 400 million years to be most numerous and diverse of the major vertevrate groups. Fish have permeated all the waters of the world, adapting an incrdible variety of forms, lifestyles and behaviors. From the seasonal freshwater streams, desert springs and salty bays to the coral reefs and created suitable niches. There are well over 20,000 known species of fish that currently inhabit the earth and many more are being discovered every year. Since salt water covers over 70 percent of the earth's surface and fresh water only 1%, one would expect that there would be many more marine (saltwater) species than freshwater species of fish. Actually 41% of the world's fish species inhabit strictly freshwater. Although quite similar in many ways to their marine counterparts, freshwater fish have adapted to a much wider range of habitats and to a greater variety of water conditions. |
