Do ocean fish of different fat content swim at different depths?

Yes. The flesh of fish that swim in the middle and surface layers of ocean waters may be as high as 20 percent fat. The fish are called pelagic, meaning "of the open sea." Among them are mackerel, herring, sardines and anchovies.

The other group, known as demersal fish -- from a Latin word meaning "to plunge down" -- are found at or near the floor of the sea, usually on continental shelves. In this category, fat content of the flesh is generally less than 5 percent and often less than 1 percent.

Fat content can vary considerably, depending on the season and food supply, and on characteristics of the individual fish, such as maturity. Muscle fat content of herring, for example, has been found to vary anywhere from 8 to 40 percent.

I have had diabetes for quite some time. At the time it was diagnosed, I became very adept at using the "exchange system." Recently I sent for a set of the revised exchange lists and noticed that the size of some fruit portions had been increased. Why is that?

The change was made to render the fruit exchanges more relevant to today's fruits. As you know, "exchanges" describe portion sizes within a category of foods that are nutritionally comparable, both in terms of calories and sources of those calories. When the exchange lists were established several decades ago, it was realistic to describe fruit portions in terms of servings providing 10 grams of carbohydrate and 40 calories. In the intervening period, the caloric density has not changed but the size of the fruits has.

Fruits today are generally bigger. The new exchange lists which specify servings containing 60 calories and 15 grams of carbohydrate were altered to reflect that growth. Amounts of fruits and juices usually served in measured portions were increased, when necessary, to fall in line with the new specifications. Of course, the fact that portion sizes have been increased has nothing to do with the total number of calories or amount of carbohydrate your diet should provide. In short, it may mean that since serving sizes are larger, the number of servings will have to be cut back a little.

The new Exchange Lists for Meal Planning are available from the American Diabetes Association, P.O. Box 25757, Alexandria, Va. 22314-3427.

My children eat seemingly endless amounts of cherries. What's their nutritional value?

Cherries are one of the delights of summer eating, but nutritionally they are in no way outstanding. Ten cherries (about one-half cup) contain 50 calories, and small amounts of vitamins B and C. The vivid color of most cherries comes from pigments that do not serve as a source of vitamin A.

Cherries, among the oldest fruits known to man, date back to prehistoric times. They probably originated in northeast Asia, but spread rapidly to Europe and North America.