Floyd Mayweather is squaring off against Manny Pacquiao ... and once again it's NOT in the ring -- this time they're fighting over gay marriage.

With the media still buzzing over Manny's controversial condemnation of gay marriage ... Pretty Boy Floyd released a counter-statement on Twitter ... saying, "I stand behind President Obama & support gay marriage."

He added, "I'm an American citizen & I believe people should live their life the way they want."

These two can't agree on anything ... so we gotta ask ...

Looking like he wandered off the set of "Goodfellas," Justin Bieber rocked a golden diamond-encrusted fish around his neck at the Mayweather fight on Saturday -- and TMZ has learned, the thing cost $20,000!!!

Sources tell us, the 14k gold "koi" fish -- designed by celeb jeweler Ben Baller -- boasts 14 carats of VVS diamonds all over (supposedly fancier than normal non-VVS diamonds). Even the chain is covered in 12 carats of diamonds.

it's unclear if the necklace was a gift or if Bieber paid for it himself.

FYI -- Koi fish represent good luck. Not like Mayweather needed it.

Last year, they engaged in the best boxer-on-octogenarian fight ever ... but now legendary sportscaster Larry Merchant says he and Floyd Mayweather are "the best friends ever."

You'll remember ... Merchant and Mayweather really got into it during their post-fight interview last September ... when Merchant famously screamed, "I wish I was 50 years younger and I'd kick your a**."

But Sunday afternoon in Los Angeles, Merchant said he and Floyd buried the hatchet over the weekend in Las Vegas and each apologized for what went down.

As for Justin Bieber's appearance at the Mayweather-Cotto fight ... Merchant said he was "trying to get some face time on television. I think he needs it badly."

We're not sure Merchant knows who the Biebs is.

Justin Bieber's appearance with Floyd Mayweather last night was months in the making -- and sources close to The Biebs tell TMZ ... Justin feels his new "mentor" is really just "misunderstood."

According to our sources, Mayweather asked Bieber four months ago to join him in Las Vegas for the Miguel Cotto fight ... and Bieber, a huge boxing fan, jumped at the opportunity.

We're told Floyd and Justin became friends after Floyd saw Justin's movie, "Never Say Never," and reached out to his camp. According to our sources, Floyd decided he wanted to mentor Justin and the two developed a relationship. 

Our sources say Mayweather tried to impart his work ethic on Justin, basically telling him he could develop the same level of "greatness" Floyd achieved ... if he worked as hard as Floyd did. 

We're told the two hit it off and Justin tells people he thinks Floyd is just misunderstood ... and that he is a really a "hard-working and clean-cut guy." 

Several judges would disagree, but whatever ...

Of course Floyd Mayweather took care of business last night against Miguel Cotto -- he had the dreaded masters of intimidation in his corner, like Lil Wayne, 50 Cent and ... Justin Bieber?

Bieber walked out with Mayweather before the fight and was in the ring with him after to celebrate the victory. 

It's unclear how the two hooked up, though Bieber did once compare himself to Mayweather in an interview. Earlier in the day, Bieber tweeted, "cinco de mayo.... #MayweatherCotto yeah @FloydMayweather today is a BIG day."

So we have to ask ...

Floyd Mayweather struck a pose with $2 million in CASH before tonight's Miguel Cotto bout -- cementing his title as best pound-for-pound boxer ... with a penchant for acting like a d-bag.

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Floyd Mayweather couldn't possibly be a racist ... because he employs sooooo many white people!

The boxing superstar has been in hot water ever since he tweeted that New York Knicks guard Jeremy Lin was only receiving attention because he was Asian. 

Mayweather has stood by his words and when he was asked about it yesterday, he proceeded to mention all the white people around him ... even pointing out that one of them "does a tremendous job."

Now that's progress.

Manny Pacquiao could decide today or tomorrow whether he will fight Floyd Mayweather Jr. on May 5th -- this according to Manny's trainer.

Freddie Roach just told TMZ Manny and promoter Bob Arum are in the Philippines, figuring out if they can put off several deals to fight other boxers ... to clear the decks for a Mayweather fight in May.

Roach is scoffing at Mayweather's tweet, in which he calls Pacquiao a "punk," saying, "He should look in the mirror. He's been ducking us for 2 years."

As for what weight class Pacquiao will fight Mayweather ... Roach said 147 lbs -- that's the upper limit of welterweight.

Of course, even if Pacquiao can rearrange his schedule, both sides have to agree on a financial deal. Roach says, "We'll do it on even terms."

Floyd Mayweather Jr. just issued the challenge the world has been waiting for -- demanding Manny Pacquiao fight him once and for all ... May 5th in Vegas.

As we reported, Floyd's jail sentence was postponed to June so he could fight at the MGM Grand on May 5th -- but so far, his opponent hasn't been determined.

Fight fans have been clamoring for Mayweather-Pacquiao for years -- and now Floyd himself is calling out Manny with the message, "Manny Pacquiao I'm calling you out let's fight May 5th and give the world what they want to see."

Floyd sounded off in the tough and hardcore forums of Twitter and Facebook -- and punctuated his challenge with, "Step up Punk."

Manny is in the Philippines ... and has yet to respond to the challenge.

Floyd Mayweather is NOT properly licensed to fight in Nevada on May 5 ... despite having the judge's blessing ... and TMZ has learned state officials are demanding to speak with Floyd in person before they will allow him to fight.

TMZ spoke with Keith Kizer -- Executive Director of the Nevada State Athletic Commission -- who tells us all fighters must apply for a license annually ... but fighters with a conviction are sometimes required to plead their case to the commission in person.

Floyd was convicted of beating his baby mama last month ... and Friday, he convinced the judge to delay his jail sentence so he could fight an unnamed opponent at the MGM Grand on May 5.

The next step is to apply for the license, but Kizer tells us it's not uncommon for a fighter to begin the process just a few weeks before their first bout of the year.  We're told Floyd has been flagged for a face-to-face ... if and when he applies.

"The commission looks at experience, integrity, character and skill to determine whether or not it's appropriate to issue a license," Kizer says.

And it ain't a slam dunk either -- the commission is known to REJECT applications  ... most famously denying Mike Tyson in 2002 after he was involved in a brawl at a NYC news conference.

Floyd Mayweather Jr. won't have to turn himself in to a Las Vegas jail until June 1, 2012 ... so he can fight in Las Vegas on May 5th ... the judge just ruled.

Floyd was supposed to turn himself in today to begin his 90-day sentence for beating up his baby mama -- but his attorney had asked the judge to postpone the boxer's turn-in date to June 1 ... to give Floyd time to train for a massive fight on May 5th against an undetermined opponent at the MGM Grand.

His attorney's justification ... Floyd's a pro who brings in hundreds of millions in profits for the city of Las Vegas -- and hey, thing's get rescheduled all the time ... no bigs.

Several of Floyd's famous friends came to court to support the boxer -- including Ray J and Lil Kim.


12:13 PM PT: Ray J and Lil Kim are real pals -- telling TMZ on their way out of court, they showed up for Floyd as an act of solidarity.



Sources close to Kim tell us, Kim and Floyd have become really close friends ... in fact, she's put her career on hold for the boxer while he awaits his sentence, canceling New Year's Eve appearances and pushing back her holiday album ... just to be there for him.