Fish Evolution

The group of aquatic animals that we call fish has evolved over 400 million years to be the most numerous and diverse of the major vertebrate groups (animals with backbones). Fishes have permeated all the waters of the world, adapting with an incredible variety of forms, lifestyles, and behaviors. From seasonal freshwater streams, desert springs, and salty bays to coral reefs and the deep abyss, different species of fish have found and created niches for themselves. There are well over 20,000 known species of fish that currently inhabit the earth, and many are discovered every year.

Since salt water covers more than 70 percent of the earth’s surface and fresh water only 1 percent, one would expect that there would be many more marine (saltwater) species than freshwater species of fishes. Actually, 41 percent of the world’s fishes inhabit strictly fresh water. Although quite similar in many ways to their marine counterparts, freshwater fish have adapted to a much wider range of habitats and a greater variety of water conditions. Hence, freshwater fish are typically hardier than their marine friends and much easier to maintain. That’s good for you.