Sometimes, the Supreme Court hears cases of monumental constitutional import. Other times, it hears fish tales.

On Wednesday, it was a case about a Florida fisherman who, in 2007, allegedly got caught at sea with some red grouper that measured smaller than commercial fishing regulations allow. A deputized federal agent claimed he told the fisherman to return to shore with some of the undersized fish to face authorities with the National Marine Fisheries Service. But, according to the government, Capt. John Yates, the skipper of the Miss Katie, had other ideas. He allegedly instructed his crew to throw the red grouper in question overboard and replace them with bigger fish.

Once ashore, federal officials weren't fooled.

But what happened next triggered the Supreme Court case. Yates was prosecuted under a 2002 law that was passed in the wake of the Enron crisis and the shredding of thousands of financial documents. The law was meant to stop the destruction of a "record, document or tangible object" with the intent to obstruct a federal investigation. But the issue before the court is whether the law was meant to cover an act of throwing fish overboard.

Justice Antonin Scalia had a hard time getting over the fact that prosecutors used the statute in the first place. The statute has a 20-year maximum, although Yates received much less time.

"Is there any other provision of federal law that has a lesser penalty than 20 years that could have applied to this captain throwing fish overboard?" Scalia fumed. "What kind of sensible prosecution is that?"

Roman Martinez, a lawyer for the government, said that the law encompasses all types of physical evidence.

"Mr. Yates was given an explicit instruction by a law enforcement officer to preserve evidence of his violation of federal law," Martinez said. "He enlisted other people, including his crew members, in executing that scheme and lying to the law enforcement officers about it."

But Chief Justice John Roberts interjected, "You make him sound like a mob boss or something."

Joking aside, however, the justices puzzled over what to do.

A lower court affirmed Yates' convictions and concluded that the term "tangible object" in the law "unambiguously applies to fish."

Justice Elena Kagan wondered if Congress, in passing the law, did mean to look more broadly than corporate fraud.

"Congress gives very strict penalties to lots of minor things," she said.

But Roberts was concerned about the leverage a broad interpretation might give the government.

"Every time you get somebody who is throwing fish overboard you can go to him and say, 'Look, if we prosecute you, you're facing 20 years, so why don't you plead to a year?"

Lawyers for the U.S. Chamber of Commerce filed a brief in the case in support of Yates. They voiced fear that if the law is read so broadly to punish small-scale fisherman, it could place "significant burdens on the business community." They argued that the law was passed in response to massive document destruction and that the government's position "threatens every corner of the American economy."

Justice Samuel Alito seemed sympathetic to that view.

"You are really asking the court to swallow something that is pretty hard to swallow," he told Martinez.

"Do you deny," Alito asked, "that this statute , as you read it, is capable of being applied to really trivial matters?"

John L. Badalamenti, an assistant federal defender representing Yates, said the law should be interpreted to cover data storage or record keeping devices, not the red grouper allegedly thrown off the Miss Katie.