PORTLAND — Fishermen around the state are hoping a million-dollar investment in the Portland Fish Exchange can breathe new life into one of the nerve centers of the state’s fishing industry.

The 28-year-old fish exchange, located on Portland’s waterfront, is critical to the state’s groundfish industry because it is Maine’s only live seafood auction, hosting sales of cod, flounder and pollock five times per week. The city-owned facility frequently houses ten tons of fish in a day and attracts local buyers and those from New York and Boston.

But the volume has dipped in recent years as New England’s groundfish industry has struggled. The exchange moved close to 30 million pounds of fish per year in the early 1990s but now averages about five million pounds per year, Portland Fish Exchange General Manager Bert Jongerden said.

City officials and the facility’s manager hope to revitalize the facility with a round of improvements that are starting this month with its roof, which is about 25 years old. The money is part of a $100 million state bond approved by voters last year.

At a recent auction, buyer Michael Twiss of Portland-based JAM Seafood and Fish Processing said the health of the fish exchange ”“ which specializes in the groundfish that live around the bottom of the water ”“ is vital to Maine fishermen and processors.

“This is it, man, period. Without this, it’s over,” Twiss said, standing over crates of dab flounder just purchased to be fileted.

The fish exchange’s decline has coincided with that of Maine’s groundfish industry at large. The state’s cod catch plummeted from nearly 2.4 million pounds in 2004 to 286,299 pounds last year, and haddock fell from more than 2.2 million pounds to 132,030 pounds in that same timeframe.

Jongerden said the improvements can help the fish exchange weather a difficult period in the industry. Ninety-five percent of all groundfish caught in the state of Maine goes through the auction, which also provides a market for New Hampshire’s vessels, he said.

“Portland Fish Exchange is a critical piece of infrastructure for the groundfish industry in the state of Maine,” he said.

The improvement work will help extend the building’s life another 20 years, Jongerden said. This first round of work on the facility ”“ a $212,855 roof repair job ”“ began in early October and Jongerden said it will likely be finished this month.

More work ”“ potentially including pier improvements and upgrades to make the facility more energy efficient ”“ is expected next winter and spring, he said.