It’s hard enough for a young actor to win over a casting agent, producer or even director to score a role.

Child star Nathan Gamble landed his biggest part to date by charming a bottlenose dolphin.

Gamble’s audition for the lead in “Dolphin Tale” meant spending some quality time with Winter, the dolphin famous for her prosthetic tail.

“There so much like humans. They have to like you and be comfortable with you,” Gamble tells Big Hollywood. “You have to be very respectful, and calm, and do the hand signals [the trainers] tell you.”

“Dolphin Tale” casts Gamble as Sawyer, an introverted boy who strikes up a friendship with a wounded sea creature. The PG film, which co-stars Harry Connick, Jr., Morgan Freeman, Ashley Judd and Kris Kristofferson, proved a surprise hit earlier this year, hauling in $71 million.

Gamble, already a screen veteran with credits including “The Dark Knight,” “Marley & Me,” “The Mist” and “Babel,” says “Tale” represented his most challenging assignment.

And he often didn’t have a line of dialogue to guide him.

“The funny thing about my character is that he leads you through the whole movie, and he says nothing in the first half. He’s a shy, emotional kid,” he says.

Gamble didn’t necessarily fudge his resume to snare the Sawyer role, but he neglected to tell the producers he had asthma before signing on. That mattered since he had to hold his breath in order to finish some underwater sequences.

He also wasn’t a strong swimmer, but some pre-shoot training took care of that – even when he had to perform scenes wearing weights to make sure he sank effectively in the water.

Gamble got his start performing in his church’s plays, but he says the role he gets the most attention for took only four days to shoot.

The youngster plays Commissioner Gordon’s son in “The Dark Knight,” a part which Gamble calls “almost like a vacation” since he flew to England for the bulk of his performance. Gamble’s character mourned the loss of his father mid-film, all part of a ruse the Dark Knight orchestrated to help flush out the Joker (the late Heath Ledger).

The “Dark Knight” connection proved frustrating only when he went out to spread the word about a “Dolphin Tale” scholastic book earlier this year.

“I went to a friend’s school and one kid kept asking questions about ‘The Dark Knight,'” he recalls. “He had these wonderfully intricate questions about that film.”

The young actor’s fans can follow his career via his own web site, NathanGamble.net, a site which lets him blog his reaction to his acting career and famous co-stars.

“It’s hard to communicate with actors,” he says. “It’s good to see what people thing so I can get better.”

Some actors, like Woody Allen, famously refuse to watch themselves on screen. For Gamble, it’s crucial to helping him track his professional progress.

“Some people don’t like watching themselves in their movies. I watch everything [I do],” he says. “What can I do better? I want to keep on progressing. I definitely think acting is a long process to be one of the greats like Morgan Freeman or Jack Nicholson. I’m sure they started out just like this … I hope.”