FISH COOKERY is straightforward and simple, and so are the necessary utensils. But they must be easy to clean, because fish is easily contaminated.

Stainless-Steel Fish Scaler

If you catch your own fish or buy them whole, a scaler is essential. The best model is made from a solid piece of stainless-steel without any moving parts. Deeply serrated edges take off the scales; the tip is turned up to avoid the chance of breaking the fish skin and the one-piece design makes it easy to clean. Recommended: Rowoco, $2.50; American Cutlery, $3.

All-Purpose Fish Knife

Select one with a good grip which will not be slippery when hands and handle are wet. One side of the knife should have a serrated edge, the other should be easily sharpened.

Stainless-steel is best for knife blades. It won't interact with any food and it's easy to clean.

The handles on the cutlery should be as waterproof as possible. Fish utensils are often soaking wet, and they need a good scrubbing after every use. If there is a slight non-skid quality to the surface of the handles, that's even better. Rosewood and Pakkawood are the finest woods, but polypropylene is probably the best. Recommended: Rowoco, $3.50; Ontario Knife, $3.

Filleting Knife

Sharpness, lightness and flexibility are the key qualities in a filleting knife. It is used to separate the flesh of the fish from its often complex bone structure. A sharp, thin point will get into every corner, and at today's prices, you want every ounce. Recommended: Rowoco, $7.50; Henckels, $15.95.

Fish Poachers

The flesh of fish is fragile. It must be handled with care or you will end up with fish sticks. A poacher, elongated like the shape of most fish, and with a built-in rack, is designed for this delicate work. There is nothing quite as visually dramatic as a whole fish properly cooked in a poacher.

An 11-inch poacher is the minimum desirable size. If you want copper and can afford it, buy copper. But any poacher big enough to hold one fish will do the job.

Make sure there is a sturdy built-in rack that will hook onto the sides of the poacher. It holds the fish out of the cooking liquid, and after the poaching and during the steaming. For poachers without this racking device, there is a back-up system. Take a couple of small, empty tuna cans, cut out both the tops and bottoms and rest your rack on it. The cans will keep the rack far enough off the bottom and out of the liquids to make the whole thing a steamer.

Some models with a bail-handle system are not recommended. The bail-wire is just not steady enough for the weight of a poacher filled with liquids and a big fish. And when the entire contraption is hot, the prospect of moving it is downright scary.

Stainless-steel or stainless-steel-lined poachers are ideal. Avoid cooking fish in aluminum which will interact with high-acid ingredients, discoloring sauces to an unattractive gray. Baking dishes should be made of ceramic or glass. These materials distribute heat well and stay hot for long periods of time.

The stainless-steel poachers with strong, sturdy, wide handles on the ends are preferable. Make sure that the handles are big enough for a good grip, even when you are using cooking mitts or pot holders. Recommended: Hoan, Rowoco, Gescor, Lamalle. Most brands are about $55.

Oval Baking Dish

To the best of my knowledge, there are no square or rectangular fish, and very few round ones, so oval seems to be the most obvious shape for most cookware. You can utilize any oval baking dish or gratin pan of porcelain, ceramic, glass, stainless steel or lined copper.

There are, however, a number of deeper oval baking dishes especially designed and marketed for cooking fish. Fish are often poached in the oven or cooked in a sauce, or baked over vegetables. The greater depth allows the fish to properly hold these additional ingredients. There are also a number of recipes that call for fish fillets to be rolled up in turbans and stood up in a group, making the depth of the dish significant.

If you use a ceramic or glass dish, remember to remove it from the oven when the fish is slightly underdone. Ceramic and glass bakeware retains its heat on a fairly high level and for a considerable amount of time after leaving the oven, the fish will continue to be cooked by the pan. Recommended: Denby, $10; Schiller & Asmus.

Fish Grills

This is the single most under-discovered piece of cooking equipment in the United States. With the enormous amount of outdoor cooking that takes place in America fish is rarely the major ingredient. Yet it is a magnificent method. The skin is crisp and flaky. The flesh is moist and tender with a slight hint of a woody taste absorbed from the barbecue briquettes. When I lived in a house with a fireplace I used it to grill fish all year round.

A fish grill is a series of metal ribs made in the classic elongated shape and designed to cradle and support the body of a whole fish, without breaking apart during the cooking. A whole fish is brushed lightly with oil, a few herbs and spices are rubbed on and the fish is placed in the grill. There are four legs extending from both sides to hold and turn the grill over the coals.

A similar fish grill with four sets of folding legs is not recommended. On a number of occasions the legs have either collapsed, or failed to stay up during a turning. Recommended: Hoan; Lamalle. Approximately $20. CAPTION: Picture 1, Fish poacher; Picture 2, Fish scaler