After studying rare and exotic marine life in Cuban waters, a group of U.S. scientists captured the island’s biggest fish.

Fidel Castro, Cuba’s Communist leader, boarded their boat in Havana on Friday night to learn about the monthlong expedition.

“We’ve had a lot of surprises scientifically and culturally,” environmental writer Bill Belleville said by telephone Saturday.

“Fidel is vital for his age and very engaging. He wasn’t just spouting rhetoric. He was genuinely interested in what we are doing.”

Belleville is among 41 researchers and crew members conducting the first deep-water exploration near Cuba.

The Discovery Channel is investing more than $1 million in the project, which employs biologists from the Harbor Branch Oceanographic Institution in Fort Pierce, Fla., and the California Academy of Sciences in San Francisco.

Getting permission to enter Cuban waters took more than a year, and the journey was delayed at least once.

The bureaucratic red tape was forgotten, however, when Castro, 71, and his armed bodyguards roared to the dock in two black Mercedes.

Clad in the familiar, olive-green Army fatigues, “El Lider Maximo” or “the ultimate leader” charmed the Americans with tales of his scuba-diving and fish-spearing exploits. Speaking Spanish through an interpreter, he asked questions about the ethics of conservation.

During his two-hour visit, Castro toured the 200-foot Seward Johnson and its four-passenger submarine. He watched videotapes of the vessel’s voyage off Cuba’s southern coast.

He examined jarred specimens of fish and aquatic life, some of which were previously unknown and have yet to be named.

“There has been so little development on Cuba’s coast, the environment is in beautiful shape,” said Belleville, who expects to return with the group Monday to Fort Pierce.

“We’re getting the first look at it and the last look, too. When investment comes to Cuba in a big way, the environment will deteriorate.”

During Castro’s visit, there was no discussion of the United States’ trade embargo against Cuba and no debate of communism vs. capitalism, Belleville said.

The only hint of politics occurred during a conversation about sharks. San Francisco scientist John McCosker remarked, “Politicians are often more dangerous than sharks.”

A laughing Castro responded, “That is very true.”