American zoos and aquariums, closed to the public indefinitely by the novel coronavirus, have joined small businesses in seeking loans under the new federal Paycheck Protection Program.

As the going gets tough, zoos also are getting cute by deploying their best marketing tools—social-media appeals featuring animal videos—to encourage donations.

Closures have cut off revenue from admissions, gift shops and food services at what, for many of these nonprofit institutions, is the busiest part of the year. Meanwhile, zoos are stuck with heavy fixed costs to care for animals.

“They’re under incredible stress,” said Dan Ashe, chief executive of the Association of Zoos and Aquariums. Even when there is no money coming in, he said, “the facility has to function at 100% to support the animals.”

Zoos across the country said they have applied for the federally guaranteed paycheck loan program but don’t know when they might receive funding. “We’re in the pipeline,” said Bert Castro, chief executive of the Phoenix Zoo.