If the salmon you buy is a deep rosy pink, it could be wild salmon -- or it could be farmed salmon fed additives to look like wild salmon. Some interest groups think consumers should be told the difference.

"It's 'buyer beware'," John Volpe, assistant professor of Marine Systems Restoration at the University of Victoria, told CTV Newsnet. "But it's very difficult to be aware if you aren't informed."

Over the last few years, salmon has become one of the top selling fish in North America. It's gone from being a delicacy to a staple in many homes and restaurants.

Some of the salmon is caught in the wild. But the 90 per cent of what you'll find in grocery stores is salmon raised on aquatic farms, which don't have the same diet as fish in the wild.

Wild salmon eat krill, shrimp shells and red algae, naturally occurring sources of canthaxanthin and astaxanthin, which make the salmon flesh pink. Without those in their diet, the flesh of farmed salmon is a shade of grey.

Most farmed salmon has pigments added to make it that attractive pink colour.

So a consumer group is pushing for what it calls truth in advertising, saying the colour in farmed salmon paints a deceptive picture of the fish for sale.

Lynn Hunter, a former member of Parliament working with the Pure Salmon Campaign, said one of the group's goals is to get artificially coloured salmon labelled in the stores.

The farmers say the colour is the result of vitamins added to the feed. Industry spokesmen say the additives, which are synthetic, mimic natural compounds that salmon would eat in the wild.

Dave Rideout, Executive Director of the Canadian Aquaculture Industry Alliance, say the additives are nutrients, not colourants, and that astaxanthin is an antioxidant which is good for the fish and those who eat them.

"We are just feeding our fish what will make them healthy," Rideout told Newsnet.

Critics of the practice say the colour is a marketing tool, since literature for salmon producers suggests people will pay more for deeper coloured salmon.

"It's got nothing to do with vitamins," said Hunter. "It's because they want to boost sales."

There's no evidence these additives are harmful to people. But European legislators are taking a cautious approach, which should be a red flag to Canadian legislators, said Volpe.

"They have cut the legal allowable use of these compounds by two-thirds" in the past couple of years, he noted.

The European Union said it reduced the level of colourants that can be fed to salmon due to concerns high levels of the additive can affect people's eyesight. A very high intake of canthaxanthin can cause crystallization on or around the retina, which can block nerve signals and cause problems such as white flashes.

Rideout insisted the additives are safe. The use of astaxanthin and canthaxanthin in feed supplements fed to farmed salmon has been approved in Canada by the Canadian Food Inspection Agency for the last 15 years.

"Not only I say it's safe," he said, "Health Canada says it's safe, the Canadian Food Inspection Agency says its safe -- the U.S. FDA says it's safe."

Representatives of the Pure Salmon Campaign, sponsored by the Washington, D.C.-based National Environmental Trust, insist that consumers have a right to know what they are buying so they can  decide for themselves.

Consumers may think they're paying for wild salmon, the group says, when they're actually getting farmed salmon. That matters because wild salmon is considered healthier, since farmed salmon contains more dioxins and other pollutants than wild salmon.

"I think most consumers would like to know colours are added," said Hunter.

With a report from CTV's Avis Favaro