Nonito Donaire remained at 115 pounds even though his body is changing for one reason — to face Vic Darchinyan in a much-anticpated rematch in August.

That fight didn’t happen, though, so THE RING’s No. 4 fighter pound for pound will fight one more time at the junior bantamweight limit and then move up — and away from Darchinyan — to 118 pounds and then quickly up to 122.

Donaire, as frustrated as anyone in the sport, hopes to find the big fights in the heavier weight classes that eluded him at 115 and below even though he is promoted by Top Rank Inc.

“This is definitely my last fight at 115,” Donaire said on cell phone from San Juan, P.R., where he’ll face once-beaten Mexican Hernan Marquez on the Juan Manuel Lopez-Bernabe Concepcion undercard Saturday night on Showtime. “This is taking too much of a toll on my body. It’s not good for me. My physician has said it’s taking too much out of me. It’s time to move on, to go up to a higher weight class.

“I was supposed to fight Darchinyan on Aug. 21. They backed out. That was the only reason I stayed at 115.”

The move up in weight makes sense. Donaire, a relatively tall 5-foot-6, has fought at flyweight and junior bantamweight almost his entire career. He’s 27 now, his muscles maturing, his body demanding to expand to some degree.

Donaire said he walks around at around at a fit 140 pounds when he’s not in training, which means he probably could fight at 126 or 130 if he wanted to.

“I think my metabolism is still pretty fast,” he said. “It’s gotten to the point, though, that strength training is building muscles in my legs, back, arms, shoulders, everywhere. I’m just a lot bigger now. I’m going to have to lose water weight. I’m going to have nothing left going down to 115. I feel better at a higher weight, especially 122.

“ÔǪ I’m not worried about this fight. I won’t be 100 percent but I’ll have more than enough to beat this guy [Marquez].”

Donaire’s decision to move up in weight also is strategic in terms of building his name.

The Filipino-born Californian stunned the boxing world when he knocked out then-unbeaten Vic Darchinyan in the summer of 2007. A rematch was a natural — but never happened. And Donaire hasn’t faced a big-name opponent since.

He had hoped to face Jorge Arce recently but that also never happened. He was supposed to have fought Fernando Montiel in April of last year but Montiel moved up in weight instead. Meanwhile, Donaire has fought only decent opponents in relative anonymity.

Donaire and his manager, Cameron Dunkin, don’t want to be too harsh in their assessment of Top Rank’s handling of the fighter because they don’t plan to change promoters. Still, it’s obvious that they’re not happy with Bob Arum’s inability to get him big fights on major networks.

They also don’t understand why Donaire hasn’t fought on the undercards of Manny Pacquiao fights to build a Filipino fanbase.

“I could be real paranoid and say that there’s a lot of politics going on,” Dunkin said. “I really don’t know. I do know that he should’ve fought on Manny Pacquiao cards. I’ve had this argument with (Top Rank President) Todd duBoef. He argues that that wouldn’t do anything (for Donaire). To me, that’s insanity.

“Fight him and let all the Filipino people see him that watch Manny fight. He would get tremendous exposure in the Philippines.”

No one is more frustrated than Donaire, who says he has suffered more from mental fatigue — as a result of the stress — than physical fatigue.

Bottom line: He feels as if he’s wasting his talent and earning power in his prime.

“I feel I could’ve really taken off,” he said. “When (Top Rank fighter) Arce was on top, they should’ve put me in with Arce. They should’ve put me in with (Fernando) Montiel. They haven’t had me fight any of their elite fighters at all.

“They’ve fulfilled their (contractual) obligation they had with me but they could’ve done a better job — getting me exposure, getting me big fights, getting on Showtime, on HBO.”

Donaire remains optimistic. With Darchinyan out of the picture, he is targeting Montiel, THE RING's No. 1-rated bantamweight who is bigger than ever after stopping Hozumi Hasegawa in April and scheduled to defend his alphabet titles on July 17 in Mexico. Montiel also is a Top Rank fighter.

Donaire wants to remain at 118 long enough to win a belt even if he doesn’t lure Montiel into the ring and then move up to 122, where he hopes fight Rafael Marquez or another prominent fighter.

That’s the only way, he figures, he can respond to his many critics who don’t believe he has accomplished enough to be on any pound-for-pound list.

“I’ve learned a lot the last few years,” Donaire said. “If you want to make a fight happen, then you have to say, ‘Let’s make it happen.’ You have to take the initiative, you have to push hard to be treated fairly. That’s what I plan to do from now on.

“ÔǪ Am I dying for a big fight? Definitely. I try not to be preoccupied with the lack of bigger names. One way or another I have faith it’ll happen. And when it does, I’ll be ready.”

Michael Rosenthal can be reached at [email protected]