I have never had an oscar before and he(or she) is only 5 monthes old. Maybe someone can help me out and tell me why my oscar is mean during to my pacu during the day. Then at night he swims real close to my pacu and shivers(vibrates)his tail in the pacus face? is this some mating ritual or an im gonna eat my tankmate dance? please help.

Your oscar is showing signs of aggression towards the pacu, that's why it's shimmering. I hope you've got a very large tank, pacu's have the potential to reach 3 feet in length.