Balinese Slapping Fish was a Nickelodeon short series aired in 1998. It was made by Fudge Puppy, who also made Very Aggressive Vegetables. In every short, orange and green fish would slap each other in a given place. None of the shorts have surfaced, but there is a Nick.com video for the short "Olympics" that displays an error when you attempt to play it.

Shorts in this series

Game Arcade

Fear Of Flying

Haunted House

Olympics

Gala Premiere

Blast Off Top 5

Fight Night

Images of the shorts

Update: 11/26/15: Fear of Flying, Olympics, Gala Premiere, and Fight Night have been uploaded by Caramell95 (A.K.A CatscratchFan4004)

https://www.youtube.com/watch?v=CYZ3LzC89HQ - Fight Night

https://www.youtube.com/watch?v=ea_bGmgYTLo - Olympics

https://www.youtube.com/watch?v=ea_bGmgYTLo - Fear Of Flying

https://www.youtube.com/watch?v=7on-x1pU12I - Gala Premiere

Update 12/19/15 Game arcade has been found by Caramell95! (A.K.A Catscratchfan4004)

https://www.youtube.com/watch?v=gP5t03M65S4 - Game arcade

Update 12/25/15 Haunted house has been uploaded by "Joey!" (TheJoeythegamer100) and Blast off Top 5 has been uploaded by "NodogonToontown" (Final Atomic Buster)

https://www.youtube.com/watch?v=IjSVZyvbwYQ - Blast off top 5

https://www.youtube.com/watch?v=YvjZ8Guv3qY - Haunted House

Kudos to A lost media fan and Nodogontoontown for proving that the videos work!