Buying a pork chop labeled "organic" is relatively straightforward: you can assume that the pig that produced it ate only organic food, roamed outdoors from time to time, and was left free of antibiotics.
But what makes a fish organic?
That is the question vexing the US Department of Agriculture (USDA), which decides such things. The answer could determine whether US citizens will be able to add fish to the growing list of organic foods they are buying, and whether fish farmers will be able to tap into that trend and the profits that go with it.
Organic foods, which many people believe to be more healthful -- while others scoff -- are grown on farms that shun chemicals and synthetic fertilizers and that meet certain government standards for safeguarding the environment and animals.
An organic tomato must flourish without conventional pesticides. An organic chicken cannot be fed antibiotics. Food marketers can use terms like "natural" and "free range" with some wiggle room, but only the USDA can sanction the "organic" label.
To the dismay of some fishermen -- including many in the Alaskan salmon industry -- this means that wild fish, whose living conditions are not controlled, are not likely to make the grade. And that has led to a lot of bafflement, since wild fish tend to swim in pristine waters, show lower levels of contaminants, and be favored by fish lovers.
"If you can't call a wild Alaska salmon true and organic," Alaskan Senator Lisa Murkowski asked, "what can you call organic?"
Instead, it appears that only farm-raised salmon may pass muster, as may a good number of other farm-raised fish -- much to the delight of fish farmers.
"With our control from hatch to harvest, that's going to be what people are looking for," said Neil Anthony Sims, president and co-founder of Kona Blue Water Farms in Hawaii, which sells a species of yellowtail that is sometimes used for sushi.
But a proposed guideline at the USDA for calling certain farmed fish "organic" is controversial on all sides.
Environmentalists argue that many farm-raised fish live in cramped nets in conditions that can pollute the water, and that calling them organic is a perversion of the label. Those who catch and sell wild fish say that their products should be called organic and worry that if they aren't, fish farmers will gain a huge leg up.
Even among people who favor the designation of farmed fish as organic, there are huge disputes over which types of fish should be included.
Trying to define what makes a fish organic "is a strange concept," said George H. Leonard, science manager for the Seafood Watch Program at the Monterey Bay Aquarium, which offers a consumer guide to picking seafood.
"I think the more you look at it, particularly for particular kinds of fish, it gets even stranger," he said.
The issue comes down largely to what a fish eats, and whether the fish can be fed an organic diet. There is broad agreement that the organic label is no problem for fish that are primarily vegetarians, like catfish and tilapia, because organic feed is available to farms -- though expensive.
Fish that are carnivores -- salmon, for instance -- are a different matter because they eat other fish, which cannot now be labeled organic. That creates a chicken-and-egg problem, so to speak. Wild tuna, swordfish, and halibut are probably not going to qualify because they are rarely, if ever, farm raised.