BELFAST, Maine — At Ducktrap River of Maine, the smokers — and employees — are working six days a week to meet the ever-increasing demand for products such as smoked Atlantic salmon, trout and mackerel, but still can’t keep up.

That’s why the company, located within the Belfast Airport Business Park, is planning a $4.5 million expansion in the next few months that should successfully double its production capacity and eventually allow them to hire 40 to 50 new workers.

“Right now, we’re maxed out,” Don Cynewski, the general manager, said Wednesday afternoon. Ducktrap River of Maine currently employs 120 full-time workers in a 45,000 square foot facility.

“The expansion is a nice investment. It’s not only adding the jobs — it really secures the jobs we already have,” he said.

The expansion is welcome news to Belfast city officials including Mayor Walter Ash, who said this week that he was “tickled to death” when he learned about it. Earlier this week, the mayor said he went on a tour of athenahealth, another Belfast company which has continued to expand its employee base and which just marked its 5th anniversary in the mid-coast city.

“Ain’t it something around here,” he said. “It seems that every other day, there’s something else going on.”

Construction on the Ducktrap expansion should begin in earnest in May, Cynewski said, with the company expecting the 21,000 square-foot addition to be completed by Sept. 1. The boosted workforce and additional space will mean that Ducktrap will produce 2,500 metric tons of smoked seafood products that it sells all over the country. Sales have grown from $17 million in 2009 to an expected $30 million in 2013. Cynewski said company officials intend to add about 10 employees a year for four or five years.

“We have had very strong demand for our product, with sales doubling over the last four years, and we are currently operating at full capacity,” he said in a recent press release. “I have been to smokehouses all over the world and feel we have some of the most dedicated employees I have seen anywhere.”

He attributed some of the company’s recent growth to an increased demand nationwide for smoked fish, and some of it to Ducktrap’s taking business from other producers. The U.S. Food and Drug Administration considers cold-smoked fish to be a high risk product, as it is a protein that has never been cooked, Cynewski said.

“The sanitation needs to be pretty high-end, and with some companies they’ve inspected, there’s been some problems,” he said. “You have to be extremely vigilant to try to be perfect. Basically, you have to be perfect.”

Ducktrap River of Maine started in 1977 in Lincolnville by Des Fitzgerald, who got into the business because he wanted to farm trout. Fitzgerald, who was with the company until 2003, learned he was doing better with sales of the smoked trout than he was with the farming end of the operation.

“It just kind of grew from there,” Cynewski said.

After a period of rapid growth in the 1990s, the company was purchased in 2001 by Oslo-based Marine Harvest, a company which has large smoking operations in countries such as France.

“It’s the world’s largest smokehouse,” Cynewski said of the parent company. “Their willingness to commit this money is not only good for future job growth but also shows the commitment they have to Ducktrap River of Maine.”