“I’m skeptical,” one NodakAngler commenter said. “The video is sure making me think,” another wrote.

Mr. Volk insists that he hooked his walleye legally on a jig, but concedes he cannot prove it. He said that the fish fought him for several minutes in a manner that indicated the hook was in its mouth, though he said never looked at the hook’s location after it was reeled in; he said he was too focused on celebrating and getting his trophy to an official weighing station.

As online blowback spread, Mr. Volk tried to make his case on NodakAngler and in Facebook posts. “I’m the lucky angler who caught the new state record walleye!” he posted on the message board. “It was caught legally in the mouth and verified by witnesses.”

Bickering over fishing records is not new. A world-record smallmouth bass caught in the 1950s was the subject of dueling affidavits about whether lead weights were added before it was placed on a scale. In 1984, a near world-record bass in Georgia could not be verified because the fisherman ate it. And in North Dakota, a walleye record that stood for 59 years carried a taint of controversy, with no photos to corroborate it. At least one person claimed that the fish had been found dead, not caught alive.

But new technology and online scrutiny have transformed the disputes. In 2009, a fisherman was required to take a polygraph exam to have his world-record claim certified. (He passed.) Just this month, South Dakota officials voided their record for a channel catfish, which had stood since 1949, after studying photos and determining that the record-holder was in fact a blue catfish.

In Mr. Volk’s case, the skepticism started almost immediately.

There were rumors about it “within a half-hour, 45 minutes of it being caught,” said Kent Yancey, a fishing guide based in Bismarck who said the debate about the walleye had been the most talked-about issue in angling circles this year. “Ten years ago, you might not have heard about it for a week.”

His fellow guide, Mr. Peluso, suggested that the walleye would have stood as a state record if not for the witness video and online pushback. “Let’s call a spade a spade,” he said. “If this fish was caught in 1985, nobody would know whether or not it was snagged or caught legitly.”