The Situation ARRESTED -- Mike Sorrentino Busted in Tanning Salon Brawl

The Situation got 2 things today ... arrested and what's gonna be a nasty black eye -- both after brawling with his brother in the tanning salon they co-own ... TMZ has learned.

Mike "Situation" Sorrentino was busted at Boca Tanning Salon in Middletown, NJ ... according to law enforcement sources.

We're told cops got a 911 call reporting a "fist fight" inside the salon ... and when officers arrived -- Sitch was arrested, and eventually booked for simple assault. He posted $500 bail ... and on the way out he explained he and his bro, Frank were scrapping over how to run the business.

We broke the story ... just last week salon employees called cops when their paychecks bounced. Sounds like that mess led to today's fight.

Situation makes it sound like he got the best of Frank in the fight ... despite his shiner, but on a related note -- check out the guns on Sitch.

He's doing a lot more G than TL lately ... or something like that.