Serie A's disciplinary tribunal said in its report that the conduct of the players and officials, who helped calm the supporters, prevented the clubs from receiving more severe sanctions.
The tribunal added the fans were involved in "a mutual, intense and continuous throwing of fireworks and pieces of tiles ripped from the stadium toilets".
The report said that public authorities ordered the match to be stopped for eight minutes during the first half. Champions Juve eventually won the game 1-0 in Bergamo.
The tribunal also handed Napoli coach Walter Mazzarri a fine of 5,000 euros (£4,200) for persistent dissent during Wednesday's 3-0 win at Bologna.