The conger eel, which is about 7ft (2.1m) long, was accidentally caught in the nets of the trawler Hope.
As it was dead when it was hauled in, the fishermen brought the creature back to Plymouth where it sold for £40.
Plymouth Fisheries said it was 131lb (59kg), just under the UK line-caught record of 133lb 4oz (60kg).
Manager Pete Bromley, manager of Plymouth fisheries, said: "It just happens to be a very unlucky big fish."
Fishermen said this photo was deceptive and the eel was actually about 7ft (2.1m) long
The eel was brought in to the fish market on Wednesday where it was caught on camera appearing to be about 20ft (6m) long and dwarfing the fishermen behind it.
But Mr Bromley said the photos were deceptive and the fish was actually about 7ft (2.1m) long.
"It was certainly very large and very unusual for our market," he said
"Conger normally live in deep water wrecks, so it is unusual to catch them on open ground."
"There's not a great deal of commercial value in them. Due to the economic downturn prices of conger have dropped."
"But it is a very impressive fish and would have made any anglers' day."
Fisherman Scott Govier was unable for comment.
Conger eels
Generally found hiding in the many wrecks which litter the South West or on reefs and rocky ground
Despite their size and power they are not very strong swimmers
Congers can reach nearly 10ft (3m) long
They will eat almost any seafood they find, from octopus to crabs to fish
They are most active at night as they leave their resting place to hunt
Source: Plymouth Fisheries/BBC Autumnwatch
Source:http://www.bbc.com/news/uk-england-devon-32748118