New York, 4 June 2012 (MIA) - Sponge Bob, nine, weighs the same as a four-year-old child, and is on a strict diet and fitness regime at the animal shelter where he now resides.
Dedicated staff at Animal Haven in New York came up with exercises to encourage Sponge Bob to move, helping him shed 3lbs in just two months.
Sponge Bob may well now be the world's heaviest cat after the previous fattest cat Meow, from Sante Fe, New Mexico, died of pulmonary failure at 39lbs, earlier this month.
Kendra Mara, Animal Haven's associate director, said: "Sponge Bob came to us when his owner went into a nursing home.
"We opened up the carrier and about ten to 15 people stood around staring at him for quite a long time, because he's the largest cat we've ever seen.
"We don't know how he became so big. We can only guess that his owner, because he was ill, was feeding him dry food on a regular basis, maybe just leaving it out, so he was able to eat whenever he wanted."
She added: "It is pretty abnormal for a cat to be able to get this big. But he has had blood work and doesn't have hyperthyroidism or anything so it appears to be just from eating."
Sponge Bob lives in a special large pen, usually given to a whole litter of puppies, and staff encourage him to jump out of the cage for daily exercise.
Staff use cat nip to keep Sponge Bob moving, along with occasional tiny cat treats, to make him to run across the room.
"To get him to run across the room, it's worth it," said Kendra.
Sponge Bob is fed a special protein diet food of lean chicken, fish and vegetables such as pumpkin, containing no carbohydrates.
Staff at Animal Haven hope Sponge Bob will continue losing one to two pounds per month, to reach a more healthy weight in around eight months' time.
He is expected to be adopted soon by a loving family, who can dedicate their time to playing with him, as well as continuing his healthy diet.
"I hope someone sees how wonderful he is and welcomes him in their home," said Kendra.