BOSTON — Those plump and tempting scallops behind the fish counter glass might be a lot smaller than they look — a sodium-based compound can bloat scallops well past their actual size. And that pollock fillet isn’t such a good deal if the price includes the layers of ice glazed onto it to keep it fresh.

This “overglazing” rips off consumers, as does so-called “soaking” of scallops, which can also alter the taste of the shellfish. At the International Boston Seafood Show last week, a top federal seafood quality officer announced his agency was increasing efforts to stop these and other types of seafood fraud.

“We’ve decided we’re going to take on the economic fraud concern,” said Steven Wilson, chief quality officer at the National Marine Fisheries Service’s seafood inspection program.

Perhaps the best known kind of seafood fraud is species substitution, when sellers secretly replace a prized species with a similar tasting, cheaper fish — say, whiting substituted for grouper, or mako shark for swordfish.

But fraud involving inaccurate food weights, caused by practices such as overglazing and soaking, is far more common, Wilson said. Inspectors at his agency find some kind of economic fraud in at least 40 percent of all products submitted to them voluntarily. And in at least eight out of 10 of those cases, inaccurate weights are the problem, he said.

“If we focus on the net weight issues we’ll drop that 40 ... percent to very, very minor percentages,” Wilson said.

The problem with detecting the soaking or overglazing is that both involve legitimate ways to keep seafood fresh, so it’s tough to tell when someone is cheating.

The law says a package labeled as 10 pounds of fish must contain 10 pounds of fish, with the ice glaze as extra, uncounted, weight. But the only way to know whether the ice is being counted is with labor-intensive inspections that match the fish weight with the weight advertised on the package.

That happened in 2010, when an investigation by 17 states showed customers were often charged for the ice in seafood packaging, sometimes as much as $23 per pound. In the four-week investigation, 21,000 packages of seafood were removed from shelves.

By The Associated Press