Debbie Schenkel, age 13, of Lansing, Michigan, for her question:

How are fishes classified?

There are boneless fishes and fishes erlth bones made of gristle. There are scaleless fishes and fishes with scales like little teeth. There are jawless fishes and fishes with long wormy shaped bodies. Almost 30,000 different species have bees classified. But about 95 per cent of them are bony fishes with flattened, streamlined bodies, classy scales and fancy fins.

The study of fishes is ichthyology and ichthyologists agree that the 30,000 assorted hinds of fishes belong in the phylum Vertebrata, along with all the other back¬boned animals. However, the simplest fishes have a nerve cord instead of a bony spine and others have backbones made of gristly cartilage. Ichthyologists also agree on the basic system used to sort their subjects into smaller and still smaller groups. But we find that they may have different ideas about some of these groupings.

Usually the various fishes are sorted into four classes and three subclasses. But sometimes Amphioxi, the simplest class, is ignored. It belongs to the lancelets, a group of small boneless, arrow shaped fishes. Some scientists regard them as a link between vertebrates and invertebrates because, though they have a spinal nerve cord, they have no bones. Next, in order of improvements, is Agnatha    the class of jawless fishes. This includes the lampreys and hagfishes, which are parasites.

The third class is Chrondrichthyes, the cartilage fishes. Here we find the sharks, one of which is the biggest fish in the sea. Their skeletons are gristly car¬tilage and instead of overlapping scales, they have hard little plates embedded in their skin. Only about five per cent of all the various fishes belong in these three classes.

The rest belong, in the huge class Osteichthyes    the bony fishes. There are so many of them that most ichthyologists sort them into three subclasses. The first group includes six species of lungfish. These oddities can breathe air and survive for long periods in dry mud. The next subclass belongs to the lobefishes, who have fins attached to stubby limbs. Until 1938, these weird ones were thought to be extinct. Then the lobe finned coelacanth was found alive and well, deep in the Atlantic.

Now we come to the huge subclass Achinopterygii    the ray finned fishes. Here tie find all the bony, scaly types that loo!_ like typical fishes. This most popular  group includes herrings and sticklebacks, catfish and codfish, basses and perches, barracudas and even eels. They are sorted accordion to their different features, usually into 33 separate orders. Each order is subdivided into families. The average fish family is a group of several genera    and each genus is a group of closely related species.

The herring, shad, salmon and trout belong in the Ciupiforms order of the ray finned subclass. Minnows and catfish belong; in another ray finned order. The largest order of this or any other group is Perciformes, the perchlike fishes. This includes the snappers and porgies, basses and butterfishes, mackerels and tunas and dozens of other species, large and small.