Quiz time: Name the most important fish in the sea.

If you said tuna, halibut, cod, flounder, marlin or swordfish, you're wrong, at least according to H. Bruce Franklin. His book, "The Most Important Fish in the Sea (Island Press, 2007) makes a powerful case that menhaden is the correct answer.

Menhaden are forage and bait fish that grow to about 12 inches. They are bony, oily, slimy and stinky. Only anglers and fisheries biologists know the species, but without menhaden the oceans would be a vastly different ecosystem.

Though people eschew menhaden, nearly every predator in the ocean depends on it. Bluefin tuna, in particular, eat menhaden. Schools of tuna attack unimaginably huge schools of menhaden, rip them to pieces and swallow the good stuff. The leftovers feed striped bass, weakfish, crabs, sharks, porpoises, gulls, terns, ospreys and virtually any other meat-eating ocean predator-scavenger.

Menhaden are so prolific and important because they are primary consumers -- they eat microscopic phytoplankton (algae) and organic debris -- which they filter from the water through a set of finely meshed gill rakers at a rate of 4 to 8 gallons per minute. This not only procures food for the fish, it also clarifies the water. And schools of menhaden can number in the hundreds of thousands or even millions so they are probably the most effective water filters on the planet.

Just two weeks ago, southern New Jersey experienced a menhaden fish kill of epic proportions. Warm water in Delaware Bay reduced the bay's oxygen content, and estimates of from tens to hundreds of thousands of menhaden washed up on shore. The stink wafted for miles. Needless to say, the residents of south Jersey are now well acquainted with menhaden.

Menhaden have been harvested commercially for several hundreds of years. Today, one company, Omega Protein Inc., turns menhaden into oil and meal for use in products, including fertilizer, food for pets and farm animals, cosmetics and fish oil.

Menhaden schools the size of football fields are spotted by airplanes and netted by huge factory ships.

Franklin worries that the day may come when menhaden, once unimaginably abundant, could disappear and forever upset the ocean's balance of predator and prey.

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