Q. A tube of anchovy paste purchased recently was delicious when eaten just-opened. I left it out overnight, however, presuming that the saltiness would prevent spoilage. The next day, upon unscrewing the cap, the paste squirted out and had changed from red to gray. It was also full of gas holes. What happened? Would it have been safe to eat?

A. During their processing, anchovies are heavily brined. The salt (especially salt extracted from the sea) carries with it a heavy load of bacteria that can tolerate very salty conditions. Unlike canned anchovy fillets, which are heated at high temperatures, anchovy paste made of pure'ed, brined anchovies is simply packed into tubes and refrigerated. Therefore, the paste has a bacterial population that will revive at room temperature.

Some of these halophilic, or salt-loving bacteria, produce gases -- carbon dioxide, ammonia, methane and hydrogen -- resulting from the breakdown of muscle proteins. And, just as with red meats, the reactions associated with spoilage also change the meat's color.

Although foul in taste and smell, the paste is probably safe to eat should you accidentally add some to food. There are at present no known food-poison halophiles.

Q. Why are anchovy fillets of one can softer than those of another? I never know what I'm getting until after I've sprung for the buck and opened the lid. I've noticed that some anchovy fillets are skinny and red whereas others have a red stripe down the middle but are white along the edges. These are almost invariably firmer and also seem to keep better. Also, how should one store anchovy fillets?

A. Mushiness is caused by the enzymatic breakdown of anchovy muscle between the catch and processing on shore. Anchovy boats venture far out to sea and must either refrigerate or freeze the whole fish in brine. Because anchovies are so small -- about 5 inches in length -- their gut enzymes easily penetrate the surrounding fillets. Cellular breakdown becomes more apparent after the fillets are removed, placed in cans with oil and heated in a retort (a steam-heated chamber).

Differences in appearance of the fillets are related to intraspecies variations. For example, beef cattle all belong to one species, Box taurus, and yet there are numerous breeds of varying shapes and color which produce meat, milk and cream of different quality. Anchovies, which are no exception to variation, are found in many oceans and survive on varying diets depending on location and season. Those fished off Peru are bound to be different from those fished and canned in Spain.

It's not surprising that the whiter fillets keep better. They contain less of the meat pigment, myoglobin. A deep-red pigment rich in iron, it transfers oxygen from the blood to the muscle. Muscles rich in myoglobin are used for quick, sudden movements. The iron has still another effect on speed: that of rancidity development. Those redder fillets are also the ones whose fats absorb oxygen and turn rancid the fastest.

Contact with air causes quick rancidity development. It's best to use all the fillets at once. However, if you must store them, remove them from the can to a glass or plastic container. Cover with vegetable oil -- olive or some tasteless oil such as sunflower -- and wrap tightly in plastic film, a plastic bag or seal with a plastic lid. These measures keep the air's oxygen away from the fish fats. Refrigeration is also paramount. Still, refrigerated, covered anchovy fillets develop an off-flavor (the first stages of rancidity) within a week.