An enticing offer at Save-A-Lot turned out to be an even worse deal. Ice accounted for nearly three of the 19 ounces of squid tubes going for $3.79 at the discount grocery store.

Both watered-down packages came from the Henry Gonsalves Co., a Rhode Island food supplier that repeatedly sold underweight frozen fish to local supermarket chains, according to a Boston Globe investigation. About two-thirds of the Gonsalves fish tested weighed less than the package label indicated.

The underweight seafood from Gonsalves is part of a persistent problem in the industry, though the company says any mislabeling is unintentional. Typically, frozen seafood is coated with ice to keep it fresh and minimize freezer burn. Some businesses in the supply chain add extra ice and include it in the weight declared on the label. Retailers end up charging for the water, and shoppers pay more money for less fish.

While individual shoppers are shortchanged in small increments, cumulatively, excess water in seafood is a serious issue, said Lisa Weddig of the National Fisheries Institute, a Virginia-based trade organization.

“Rather than looking at this as 30 cents here and 30 cents there, we should be looking at this as a $69 billion seafood industry and these practices could be costing the industry and consumers tens, if not hundreds, of millions of dollars in the end,” Weddig said.

The National Oceanic and Atmospheric Administration, which runs a seafood inspection program, said it finds economic fraud in at least 40 percent of products voluntarily submitted to the agency for testing by processors and other businesses. At least eight out of 10 cases involve inaccurate weights, according to Steven Wilson, chief quality officer of NOAA’s seafood inspection program.

A Globe survey of 43 seafood samples from supermarkets across Massachusetts showed about 1 in 5 glazed with ice weighed less than the net weight stated on the label, which is supposed to exclude packaging and glaze. For example, scallops sold at a Walmart store weighed roughly 13 ounces, not the 16 ounces listed. Crab meat at Kyler’s Catch in New Bedford, labeled as 6 ounces, weighed 5 ounces. The newspaper hired an independent lab to weigh the fish after removing the glaze.

The Globe then conducted a months-long examination of three local seafood suppliers. Dozens of additional samples from five supermarkets that use those suppliers were collected and sent to the lab to be weighed.

Gonsalves had the most pervasive problems: About 66 percent of the 38 Gonsalves fish samples from Market Basket and Save-A-Lot supermarkets weighed less than was stated on labels, according to results from UL-STR, the Canton lab hired by the Globe.

The US Food and Drug ­Administration requires food labels to have the proper weight, but state and federal officials who conduct weight tests permit variances. The results of testing on Gonsalves fish were far outside those allowances.

Henry Gonsalves, president of Henry Gonsalves Co., said overglazing is endemic to the industry. He said his firm, which sells about $10 million worth of seafood annually, buys mackerel and frozen squid in bulk and workers at the company’s Smithfield headquarters hand-fill bags of the already-glazed fish. The business also sells fish to chains such as Shaw’s and Stop & Shop.

Gonsalves said he tries to make up for the ice glaze by putting more fish in packages, usually several ounces above the net weight listed. But he conceded that the Globe testing suggests he is falling short in some cases.

Eastern Fisheries in New Bedford, the world’s largest supplier of scallops, distributed the Walmart sea scallops that weighed about 13 ounces, not 16 ounces as labeled. Additional testing found bay scallops in three of 10 bags from a Worcester Walmart weighed less than the 16 ounces listed on the package, but were within half an ounce of the declared weight.

High Liner Foods USA, based in Danvers, was the only distributor whose weights tested accurately in all cases. Company president Keith A. Decker said fish is individually quick frozen and then moved through or dipped in a water tank. Workers bag and weigh the fish by hand, and regularly monitor weights on the production floor. “We try to achieve 100 percent of declared weight,” he said.