They rise at night, visible only when the sky is black and the moon is hidden — thousands of opaque creatures swimming near the ocean's surface, seeming to light up the sea.

Pacific krill, the tiny shrimplike crustaceans that travel in swarms and are food for everything from rockfish and herring to seabirds and whales, are so high in protein they form the backbone of the Pacific Ocean food chain.

But krill caught in Japan and Antarctica are also freeze-dried and made into goldfish feed, sold for pharmaceuticals or crushed into powder to feed young fish in fish farms so their flesh will develop a naturally healthy reddish sheen.

Now federal fish managers are wrestling with a question they plan to settle this spring: Should commercial operators be able to fish for krill in U.S. waters?

Currently, there is no krill fishing on the West Coast, and the practice is banned in near-shore waters off Washington, Oregon and California. The reason: Krill are susceptible to dramatic changes in climate that which can cause wild swings in population levels, and krill are critical to ocean health.

"Krill feed on the tiniest organisms in the sea, and many, many animals rely on krill," said Mike Burner, a staff officer with the Pacific Fishery Management Council, the government body that oversees commercial fishing off the West Coast. "They're one of the most important species in the food web."

But working its way through Congress is a controversial White House proposal to open up vast areas of federal waters to fish farming — a move to increase aquaculture by 500 percent and reduce a seafood trade imbalance.

Such an explosion in aquaculture could make krill a hot commodity — a way for fishermen to feed the fish that would feed the world.

"There's been speculation that growth in aquaculture will produce a major market for harvested krill," Burner said. "In that scenario, a krill fishery is not too hard to imagine."

Pushed into action by the managers of federally protected marine sanctuaries, the Pacific Fishery Management Council plans to decide in March whether to extend the ban to the open seas of the Pacific.

On one side are a handful of fishermen who see a potential new market for a troubled industry.

"My whole point is why would you stop something before you even know what it is or whether it's harmful," said Ryan Kapp, a Bellingham-based sardine fisherman who urged the council not to ban krill fishing. "With the fishing industry in the shape it's in, if you could sustain a 10-boat fleet, you'd have some employment and not be doing anything to the resource."

Kapp pointed to krill operations in British Columbia, where fisherman bring home about 500 tons of krill a year from waters believed to hold more than 1 million tons of krill.

"We're pretty small-time," said Glenn Budden, head of the B.C. Krill Trawlers Association. "You can shine a flashlight into the water and see them as they go by the boat; you can almost just count them. Then when you pack it all together in the back of the boat, it's like briny, briny ground beef."

But environmentalists counter that ocean conditions have been in a period of flux and that allowing krill fishing could set a dangerous precedent.

Last summer, when upwelling currents that bring food to the ocean surface failed to materialize off the Northwest coast, krill disappeared "and seabird die-offs were the most immediate result," Jim Ayers, who was chief of staff when Tony Knowles was Alaska's governor and now represents the environmental group Oceana, wrote to federal officials.

Environmentalists also fear a program that could grow to rival those of the waters off Japan or Antarctica, where massive trawlers — boats that drag huge fine-meshed nets behind them — haul tens of thousands of pounds of krill each year.

The fishery-management council has signaled it's leaning toward expanding the ban. But there's no guarantee.

"I generally don't like to speculate on what they're going to do," said Burner, with the council. "It's a fairly safe bet that they'll pass the ban. But it's no forgone conclusion."

Size: 22 to 38 millimeters long

Lifespan: 8 months to 2 years

What they eat: microscopic plants and animals, such as fish eggs and larvae

What eats them: groundfish, salmon, squid, whales, seabirds

Range: Bering Sea to Baja California

Where they hang out: 100 to 400 meters deep during the day; near the surface at night

How they travel: in large, dense swarms

• Seattle Times