The Egyptian player, who has scored in all five games he has played joining Mainz from champions Borussia Dortmund in January, must pay 6,000 euros for "unsporting behaviour," the German federation said on its website.
The DFB's disciplinary tribunal said Zidan climbed the fence in front of the fans and began singing along with them. It said the 30-year-old had accepted the decision.
Zidan, who made only two appearances for Borussia Dortmund this season before the move, had already apologised for the incident.
"I regret getting carried away in the euphoria following our home win," he said.
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