The 22-year-old midfielder slapped a 15-year-old Everton fan in the Bangkok Radisson in the early hours of last Friday and then rounded on team-mate Richard Dunne when he stepped in as a peacemaker, an act that left the Republic of Ireland defender nursing a bitten finger and badly bruised foot.
City launched an immediate investigation into the incident and though they stopped short of placing Barton on the transfer list, the former England Under-21 international has been left in no doubt the club will not tolerate another breach of discipline.
Barton, and his agent Struan Marshall, attended a meeting with the manager, Stuart Pearce, and the chairman, John Wardle, yesterday at which he explained how he had been provoked by the supporter but admitted his responsibility for what followed.
City spokesman Paul Tyrrell said: "Joey has expressed his deep and sincere remorse over the incident and is keen to make amends to this football club and our fans who expect the highest standard of behaviour from our players. He has apologised to those involved and has accepted his fine unquestioningly."
Barton added: "I understand the distress I have caused to everybody concerned and want to apologise for my actions. I am grateful for the support I have received from the club and my friends and family."
The fine will cost Barton over £120,000, and exceeds the six-week fine he was given by City for stubbing a lit cigar into the eye of former reserve player Jason Tandy at a Christmas party in December.
Darius Vassell, meanwhile, is determined to kick-start his career at City and help the club to push for a place in Europe. The 25-year-old, who has signed a four-year contract, completed his £2m move from Aston Villa yesterday after agreeing personal terms.
Vassell believes that under Pearce, City can make up for the club missing out on the Uefa Cup last season.
"If you look at where they could have finished, it was a fantastic achievement," Vassell said. "Hopefully, we can build on that."