It's one thing to get a goldfish because your daughter begs for one. It's quite another to end up with a hundred-pound rodent who has more than 2,700 Twitter followers.

Caplin Rous is a capybara. Related to the guinea pig, the capybara is the largest species of rodent. Though they're native to South America, Caplin was born in Texas and lives in the town of Buda with Melanie Typaldos, who never expected this animal to take over her life quite the way he has.

Typaldos says it all started on a trip to Venezuela, when her daughter Coral got to hold a young capybara and “fell in love.”

“After we got back, she pretty relentlessly pestered me about getting one for a pet,” Typaldos says. “Since Coral lived in an apartment and was planning on spending a year in Asia, she couldn't have a pet capybara herself so, she felt, it was up to me to fulfill her capybara vision.”

Even capybaras that are bred in captivity like Caplin are not domesticated animals, so early handling and contact is critical for them to be comfortable living with people. Typaldos got Caplin when he was only 11 days old, and took him to work every day for the first three months. Then, “someone complained there was a furry, pig-like animal in the building,” and she took a month of vacation and stayed home with him.

Caplin Rous is now 2 and a half. The second part of his name, which Typaldos pronounces like “rose,” stands for “Rodent of Unusual Size” (a reference to the movie “The Princess Bride”). He's also a rodent of unusual abilities. He can walk on a leash and even do some tricks, but Typaldos says it's important not to exaggerate any similarity to a dog doing tricks.

“Dogs have thousands of years of being trained to be subservient to people,” she says. “A capybara will not do a trick just to make me happy. The quality of the trick is very dependent on the quality of the treat.”

Most people who keep capybaras keep them as farm animals, like a sheep or goat, but Caplin basically lives indoors with Typaldos (he eliminates in a pan of water in her bathroom). Outdoor space is necessary as well for grazing and swimming in his pool; in the wild, capybaras are semi-aquatic, diving into rivers to escape predators. Somewhat ponderous on land, capybaras are surprisingly graceful in the water.

“On land he's not very active,” she says. “When he's in the water he's like another animal. That's where he's really the happiest.”

There's no way of knowing how many private individuals own capybaras, but Justin Damesta, a breeder in Alvin, says that he sells five to 10 of them a year as pets.

Damesta recommends that a pet capybara be raised indoors for the first few months and then kept outdoors with sturdy fencing, a heated shelter and a pool. Potential buyers who contact him are usually fairly well informed, but, he says, “I have and will turn down people I don't consider qualified or capable.”

Some other pet capybaras also can be followed on the Internet, such as Dobby in Seattle. But Typaldos is probably unique in the way she has made the capybara her mission: She spends a couple of hours a day updating Caplin's Internet presence on a blog and social networking sites.

When asked how much time it takes to care for a capybara, she says, “I spend all my time with him, but that's a matter of choice.”

Caplin's Web activities are partly fun — such as interactive games of “Rodent Jeopardy” — with a serious educational purpose, too. “When I was thinking of getting him, there was nothing on the Web about getting a pet capybara,” says Typaldos. “That was a large impetus for the blog. They're not the right pet for most people.”

Typaldos has a background in biology, and also keeps horses and reptiles. Her property is big enough that Caplin can graze and swim, and she lives in a climate appropriate for a tropical animal.

On her blog, she's honest about the problems in caring for a capybara. When people ask her about getting one, she tells them first to read her whole blog, including the entries about when he has bitten her.

But Typaldos also sees Caplin as an ambassador of sorts.

“People don't like rodents,” she says, but many rodents make good pets. Her kids had pet rats when they were young. “If someone says something bad about rats, on the blog or Facebook, he'll always step in and say something.”