Most of us have a better understanding of how to fix a car than we do of how to purchase and store fish. An experienced fisherman can determine the quality of a fish with a simple glance at it. It's not that easy for the rest of us.

Of course, the experienced fisherman often has the advantage of having seen the fish come out of the water. We, on the other hand, must look at the fish carefully, touch it, even lift it up and smell it.

Don't feel embarrassed to ask that you be allowed to examine the fish more closely than by simply looking at it through the glass window of a refrigerator case. You should inspect fish carefully being buying it, since fish being sold at our neighborhood supermarkets or at the local fish shop often is not as fresh or of as high quality as it should be.

The following guidelines, which are based on the recommendations of the Alaska Seafood Marketing Institute, explain the proper way to be assured of good quality when purchasing fresh and frozen fin and flat fish. The guidelines also explain how to keep that fish moist, to prevent odor absorption and development, and to minimize deterioration with proper storage. Shellfish are another matter and extremely difficult to evaluate according to any kind of general guidelines. Purchasing Fresh Fish

* Choose whole fish or large pieces whenever possible.

* Only a mild, pleasant seafresh odor should be apparent. A strong or objectionable odor indicates poor quality.

* The eyes of whole fish should be bright and clear.

* Most of the scales should be shiny and intact, adhering tightly to the skin.

* The skin and flesh should be bright and characteristic of the species.

* The flesh generally should be firm and resilient to the touch. Only some flat fishes, such as sole and flounder, should have softer, less resilient flesh.

* Fillets and steaks should look freshly cut and be moist and firm. There should be no reddened areas in the flesh caused by blood retention or bruising.

* Prepackaged fish should have no liquid within the package. Absorbent paper under the fish should be dry or only very lightly moistened. The wrapping should be clear and moisture-free, with a minimum of airspace between the fish and the wrapping. Storing Fresh Fish

* Quickly rinse under running cold water and pat dry. If prewrapped, discard the original packaging.

* Wrap the fish tightly and securely in moisture-proof paper or place in a rigid, airtight container. Never store fish in water, which causes rapid deterioration.

* Store in a refrigerator set at 33 to 35 degrees and checked with a refrigerator-freezer thermometer. Fish stored at 32 degrees has twice the shelf life of fish stored at only 5 degrees higher.

* Use within two days of purchase.

* Only as a last resort should fresh fish be frozen at home, as the process greatly affects the texture and quality of the fish. Purchasing Frozen Fish

* There should not be signs of dehydration or freezer burn.

* It should be solidly frozen and show no evidence of thawing (partial or complete) and refreezing (such as frozen liquid under the fish).

* It should not be bruised or damaged.

* Do not buy frozen fish that is stored above the "load line" in the display case. Frozen fish stored above that line may have a significantly reduced shelf life.

* If there is a "sell by" or "use by" label on the package, only buy the package if you will be able to use the fish by that date. Storing Frozen Fish

* Commercially wrapped and frozen seafood should be taken home immediately after purchase and stored unopened in a freezer with the coldest possible temperature.

* Storage life doubles with every 10 degrees below zero fahrenheit.

* Fish stored at temperatures above zero degrees should be used within 10 days.

* Use freezer paper and never freeze fish wrapped only in waxed paper, parchment paper, plastic paper, plastic film or aluminum foil.

* Date packages and use within 30 days.

* If a frozen package is opened to divide into smaller portions that are to be returned to the freezer, the fish must be kept completely frozen. Discard the original packaging, wrap the fish securely and tightly in freezer paper and, if possible, place in an airtight container that conforms closely to the shape of the package, leaving minimal airspace between the fish and the container. Home Freezing Fresh Fish

* Home freezing of fresh fish is not recommended since the drop in temperature is slow and most of the loss in quality in frozen fish occurs during the drop in temperature from 30 to 23 degrees. Commercial freezing ensures that fish pass rapidly through this temperature zone.

* Slow freezing causes considerable loss of flavor and texture of fresh fish, so consider home freezing only when absolutely necessary and only with the freshest, finest-quality seafood available.

* If you must freeze fish at home, wrap the fish in small packages as large portions take longer to freeze.

* Stack the fish loosely with air circulation around the packages (overloading will slow freezing time) into the coldest part of the freezer. Thawing Frozen Fish

* Thaw frozen fish in the refrigerator at 33 degrees to 35 degrees.

* Never thaw at room temperature or under running water, as fish that is thawed quickly will decline significnatly in the quality of its flavor and texture.

* Thawing fish at temperature above 40 degrees greatly increases chances for spoilage due to rapid growth of unwanted bacteria.

* Never refreeze thawed fish.