So you thought it was safe to go back in the water?

This is partly down to the way Katzenberg has played the game. He screened just 20 minutes of Shark Tale at the Cannes film festival. Now he is planning the most spectacular world film premiere in history, at the Piazza San Marco, Venice, on September 10. The historic square will be closed while 5,000 invited guests watch the full movie on a giant screen. Between the initial appetiser and the main course, the clamour has grown. It is based mostly on the 20-minute teaser, but also on what has been heard on the grapevine and from the actors involved.

From what I have seen, it looks like a must-see. To watch a great white shark called Don Lino, voiced by and looking like Robert De Niro, engaged in deep-water conversation with Martin Scorsese, unmistakable as a puffed-up fish (in all senses) called Sykes, is probably worth the entrance fee.

Here is an example. De Niro’s gravelly voice tells Scorsese: “I look you in the eye and tell you what’s what.” Scorsese’s impatient tones: “And what?” De Niro: “What? What, what?” Scorsese: “What nothing — you said ‘what’ first.” De Niro: “I didn’t say ‘what’ first. I asked you what.” And so on, in mafia-fish style, with remarks such as: “It’s a fish-eat-fish world. You either take or you get taken.”

And there is much more action on the reef. Will Smith voices Oscar, a hustler kind of small fish who is able to talk his way out of trouble. If Smith sounds as if he is making up some of it as he goes along, it is because that’s exactly what happened. Jack Black is Don Lino’s son Lemmy, a closet vegetarian. Renée Zellweger pops up as Angie, an angelfish with a secret crush on Oscar. Angelina Jolie is there, playing Lola, a femme fatale dragon fish.

That is enough Oscar-winning wattage alone to light up the ocean.

There’s more: Peter Falk, late of Columbo, as an ageing shark, Don Brizzi; Michael Imperioli, Christopher in The Sopranos, as Don Lino’s older son, Frankie, who bites everything in sight; Vincent Pastore, also of The Sopranos, as an oily octopus called Luca. Then there are the street-sharp sounds of Ziggy Marley, son of Bob, and Doug E Doug, playing a pair of Rastafarian jellyfish, Ernie and Bernie. Sounds good? Well, it looks great.

The animation is now so sleek and refined — think of an even more sophisticated Shrek 2 — that the audience can be forgiven for imagining it is actually seeing the all-star cast in action, rather than the fish. “This is a cutting-edge animation movie,” observes Katzenberg, somewhat unnecessarily. But he denies that his underwater tale has been in any way influenced by the success of Disney’s Finding Nemo. “Shark Tale has been three years in the planning and the making,” he says. “Nothing has been left to chance, from the choice of stars to the music.”

Katzenberg himself leaves little to chance. But he could not stop his rise at Disney coming to an abrupt end when the company’s chief executive officer, Michael Eisner, refused to pick him as his second in command. He won a long legal battle, settled with a $275m payoff based on profit share, and keeps on hitting back through DreamWorks. “Revenge has nothing to do with any of this,” he insists, po-faced. “My only aim is to do well for DreamWorks and share my enthusiasm for making these kinds of movies.”

Katzenberg seems the sort of man only Hollywood could produce. He speaks in headlines and hyperbole, with phrases that could be straight from the corny script of a film mogul. “The movie gods granted my wish in getting Will Smith to play Oscar,” he says. “The character dreams big and schemes bigger. And then he gets into trouble, trying to chase after the things he dreams will bring him happiness.

“When we were developing the movie, I had a dream of my own — to get the No 1 actor in the whole wide world, who would be absolutely perfect for the part. He had to have charm and charisma, be someone the audience would instantly fall in love with. On top of that, he had to be the kind of character who could believably talk his way into and out of any kind of trouble. Who else but Will?” Well, probably the person he would have hired if Smith had turned it down.

But no matter. Katzenberg is in full flow now. “I got a little greedy and went back to those movie gods for a second time,” he says. “I thanked them profusely for Will and asked them if they could get me Jack Black to play Lemmy.” Granted, obviously. Then there was Lola: “I sold my soul to the devil, and we were blessed and lucky to get one of the most beautiful women in the world — Angelina Jolie,” he says.

After a build-up like that, what can the stars themselves say? “Jeffrey is a powerful man in Hollywood,” says Smith. “He comes to wherever you are and lays out the fact that you may never work again unless you do the project.” He is joking, of course, but he was clearly not going to put a refusal to the test. “It was a case of ‘Why not?’,” he adds. “I don’t have to dress up and go on show. I was also given the option to put in some of my own material.”

This is an added advantage with Smith. He is a bright man with a machine-gun turn of phrase. Like Eddie Murphy’s Donkey in Shrek, he can also talk at a faster rate than anyone else in the film. He followed the four stages of computer-generated animation — the pencil drawing, the rough animation and layout, the lighting and the colour — with hours of recording sessions. “The script was very loose in the early stages,” he says, “and the story was being worked while I was performing, so I got to try plenty of lines. There is a liberating space in there, with my headset on, and I was allowed to try new things all the time. The message was, ‘Try anything, be anything.’”

He also enjoyed one of the biggest advantages of voicing animation: “For the first time in my life, I didn’t have to go into hair and make-up, or think about the clothes I wore. I just turned up, put on the headphones and started speaking. I could also have as many takes as I liked.”

For Black, it was another huge step forward at the age of 35, after years of being an also-ran. Hit films in the past four years, such as Shallow Hal, High Fidelity and School of Rock, have suddenly propelled him into the first division. And, truth be told, when we spoke at Cannes, he looked a little shaken by the fuss. “The first and last time I came to the festival was 12 years ago,” he says. “I had a small role in the film Bob Roberts. I was not invited, but I came anyway. I couldn’t get to see any of the movies.”

He has a pleasant, self-deprecating touch when discussing the fact that he’s now staying in the best hotel in town and is invited to every screening and every party. “Whatever else might happen to me, thanks to Shark Tale, I can say I worked in a film with Robert De Niro and Martin Scorsese,” he says. “We’ve never met, because you do the voices in isolation. But it’s there on the credits, isn’t it?” He also makes light of his unusual appearance, which is not built for Hollywood stardom. He is 5ft 6in and 13st. “I am going on a strict diet,” he says. “It is the ‘Eat whatever you like so long as it’s not too much’ diet.” But looks did not matter on Shark Tale. “That suited me,” he says, with a smile. “I want to do more.”

Jolie (of whom Will Smith said: “When I first saw Angelina’s fish, I started eating sushi”) openly declares that this is going to be her biggest success. And that is despite her lead roles as Lara Croft in the two Tomb Raider films and a best-supporting-actress Oscar for Girl, Interrupted. “I am not so good at playing around with stuff as Will or Jack,” she says. “So I stuck to the script and said what I had to say. But the biggest shock was when I saw my fish on screen. She looked stunning — and I do not look as good as that. She also bats her eyes a lot, and I thought, ‘I never do that.’ All my friends have told me, ‘Yes, you do.’ So the animators pick up things that we are not even aware of.”

For Katzenberg, then, nothing has been left to chance: not the casting, the marathon animation sessions, the hype, nor the timing of the release. He even changed the original title, Shark Slayer, because it sounded too aggressive. “You have to hire great actors and the best animators, and give them a free environment,” he asserts. “Then they give you gold.”

The feeding frenzy is about to begin.

Shark Tale is released on October 15