Mary Jo Middlebrooks, age 12, of Shreveport, La., for her question:

Is an eel a fish or a reptile?

The slippery eel looks very much like a water snake and, of course, all the snakes are reptiles. Fish have scales and fins and most of them have flat, streamlined bodies tapered at both ends. The snaky eel does not look at all like the average fish. Nevertheless, he is a true fish.

Fish are always slimy to the touch and most of them have small, glassy scales embedded in their skins. Reptiles have dry skins, usually covered with leathery scales. The eels, like the fishes, are always slippery and covered with slimy mucus. Most reptiles have legs and most fishes have fins. None of the eels have legs and all of them have fishy fins.

Some of the reptiles live in the water, but all of them have lungs for breathing oxygen from the air. The fish have gills for taking oxygen from the water. And every eel has fishy gills. If We examine the inside of any reptile, we find a heart divided into four chambers. Every fish has a heart with only two chambers. The eel has a two chambered heart.

The eel looks like a water snake, which is a reptile. But he has many features that disqualify him as a reptile. He has no features to disqualify him as a fish. The various eels, large and small, belong in the class Osteichthes   the bony fishes.

The common eel of the fresh water creek may be several feet long. This animal is a female, for the males of this species never come far inland. There are fishy scales buried deep in her slimy skin. Her fins form a flat fringe around the lower end of her snaky body. She has a pair of small, gauzy fins where you would expect her ears to be. In front of these fins, the eei has a pair of gill. Slits for taking oxygen from the water.

There is no doubt about it, the eel is a fish. She is not a close relative of the electric eel, who is classified with the carps and the catfish. But she is first cousin to the whopping conger eel and to the ferocious moray eels of the coral reefs. All these snaky fishes are classified in the order apodes, meaning the footless ones.

The eel develops from an egg through a larva stage. And for the first year of his life, a larva eel looks like an ordinary fish. He has a flat body, tapered at both ends. Long ago, eel larvae were found in the ocean and no one guessed that they were baby eels. They were named leptocephah, meaning little heads. These fish like eel larvae are still called leptocephali, as they were when scientists thought they were unrelated to the eels.