Donna Lipscomb, age 12, of Charleston, West Virginia, for her question:

How many fish species are there?

In 1968, a living coelacanth was dredged up near the coast of South Africa. The event was remarkable because ichthyologists had assumed that this fish species became extinct ages ago. In the past few years, marine biologists have discovered weird and wonderful fishes living in the impossible ocean abyss. Hence, it is not likely that all the fish species are known to man. However, the known species out number all the other back boned animals  and we can expect the list to grow longer.

Roughly 20,000 bony fishes have been identified and classified, plus a large assortment of sharky fishes whose bones are gristly cartilage. The fishes come in a vast variety of shapes and sizes and at least a few species are at home in almost every body of water from pole to pole. Some live in mountain lakes almost three miles above sea level. In order to qualify as a fish, an animal must have gills and fins. And almost all fishes have scales instead of fur or feathers.

Naturally, the known fishes have been classified in related groups and given scientific names with clues to their special features. As vertebrates they belong in the advanced Phylum Chordates. At one time, all of them were grouped under Pisces, the fishes. Now they are separated into two classes. The Class Chondrichthyes, meaning the cartilage fishes, includes the sharks and rays, the dogfishes and the chimaeras. The vast majority of fishes are in the Class Osteichthyes, the bony fishes. Each class has a number of orders formed from groups of related families. Each family is a group of closely related genera. The scientific name of each fish gives his genus and his own personal species.

The salmon and trout share a family in the same order, the eel and the electric eel belong in different orders. One family has about 2,000 carp species, another family belongs to about 25 sturgeons. Every fish species is specially adapted to his own way of life in his favorite watery environment. The numerous fishy details are fascinating. But the past history of this hardy clan is downright fabulous.

The fishes were the earth's first vertebrates and their dynasties date back at least 400 million years. Their early ancestors were toothy and armor plated. They gradually improved and after 100 million years their descendants greeted the Devonian Period with a flourish. Numerous capable species thronged the shallow, fresh seas and made this the Age of Fishes. In this world of 300 million years ago, the fishy Pisces were more advanced than any other creatures on land or in the seas. Millions of years later, the mighty dinosaurs reached their heigh day and declined. But the fishes continued to advance, on through the present Age of Mammals. Herring, salmon and mackerel species arrived with the dinosaurs. Electric eels perfected their shock treatments after the dinosaurs had departed. The pikes and certain minnow species developed in the Miocene Epoch about 26 million years ago, just about when the first apes and flowering plants appeared on the dry land.