Aykroyd, Fisher's friend and one-time boyfriend, also paid tribute.
The event, featuring humour, music and dance, was a chance for fans to remember the legendary Hollywood pair following a private service earlier in the year.
Fisher said he never saw his mother turn a fan away. "As the two-hour service began, Todd told the crowd that it would be more of a show than a memorial, because "[Debbie] liked shows and parties". Family, friends and fans attended the service, which was public.
A troupe from Reynolds' dance studio performed an homage to "Singin' in the Rain", the film that catapulted Reynolds to stardom at age 19. Across the stage, near a piano, sat an empty chair with Reynolds' name on it.
Describing the moment his mother Debbie died, Mr Fisher continued: "She literally asked permission and said she wanted to be with Carrie". Todd Fisher, son of Debbie and brother to Carrie, shared a very personal story from after his sister's passing on December 27, 2016. It was a very peaceful exit that only my mother could've orchestrated. There were plenty of Reynolds' and Fisher's friends and family in attendance.
Fisher's former beau Aykroyd took the podium to recall their friendship.
Lamenting on her fate, he said: "If I'd been with our beloved showboat, I might have been able to save her again". "As long as we live, they too shall live".
The ceremony was attended by several stars, including Rene Russo, Beverly D'Angelo, "Dallas" actress Morgan Brittany, actor-director Fisher Stevens, "Brady Bunch" actress Susan Olsen and actor Griffin Dunne.
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Carrie Fisher shot to fame as Princess Leia in Star Wars. Fisher's response? "It's bad".
After the first screening, they both knew she had been wrong.
For example, R2-D2 took the stage. "It wasn't with Carrie, but she did arrange it", he said drily, to howls from the audience. "But she literally looked at me and said, "I want to go be with Carrie" and closed her eyes and went to sleep".
Aykroyd, who was briefly engaged to Fisher decades ago, before she Wednesday singer-songwriter Paul Simon, brought a bit of humor to the service. He recounted how Fisher took him on worldwide trips and "gave me so many firsts".
"When Carrie left us, my mother and I were talking".
It was one of many tales about the actresses that drew boisterous laughter.
Hundreds gathered in L.A.at the Forest Lawn Memorial Park-Hollywood Hills' Hall of Liberty.
The afternoon was billed as a celebration of their careers, and it included a memorabilia display of a dress worn by Fisher in the original "Star Wars" and a life-size R2D2 unit that lights up and occasionally beeps.