SAN FRANCISCO – What’s black and white and warm all over? A penguin in a wetsuit, naturally.

Sounds like a joke, but it’s quite serious for biologists at the California Academy of Sciences, who had a wetsuit created for an African penguin to help him get back in the swim of things.

Pierre, a venerable 25 years old, was going bald, which left him with an embarrassingly exposed, pale pink behind.

Unlike marine mammals, which have a layer of blubber to keep them warm, penguins rely on their waterproof feathers. Without them, Pierre was unwilling to plunge into the academy’s penguin tank and ended up shivering on the sidelines while his 19 peers played in the water.

“He was cold; he would shake,” said Pam Schaller, a senior aquatic biologist at the academy.

Pierre’s species of penguin is accustomed to temperate climates, unlike many of their cousins. The birds are nicknamed Jackass penguins because they make sounds similar to braying donkeys, quite startling the first time you hear it in an aquarium.

Schaller first tried a heat lamp to keep Pierre warm. Then she got another idea: If wetsuits help humans frolic in the chilly Pacific, why not whip up one in a slightly smaller size?

Staff at Oceanic Worldwide, a supplier of dive gear based in San Leandro, were enthusiastic about making a real penguin suit.

“We were really excited to do it,” said Teo Tertel, company marketing specialist. “We heard most of these penguins only live to 20, and our little buddy there was already 25. Anything we could do to help them, we were all for it.”

Schaller conducted fittings to design the suit, which fastens with Velcro at the back, covers Pierre’s torso and has small openings for his flippers.

“I would walk behind him and look at where there were any gaps, and cut and refit and cut and refit until it looked like it was extremely streamlined,” she said.

One concern was that the other penguins would reject Pierre in his new duds, but they accepted his sleek new look.

Pierre was outfitted with the suit about six weeks ago.

Since then, he has gained weight, grown back feathers on his hind parts and is again acting like his feisty, alpha-male self. On a recent visit, Pierre waddled around the tank, taking brief dips and standing on a rock next to his mate. He blended in well, although he was the only penguin with a black tummy.

Schaller can’t say for sure whether the wetsuit allowed Pierre to recover his fine feathers, but “certainly we were able to keep him comfortable during a period of time that would have been very difficult for him to stay comfortable.”

With his plumage restored, Pierre is being weaned off the suit, taking more and more dips in the buff.

There are no plans to make him a matching surf board.