Blue Jellyfish are a rarely seen color variant of jellyfish and are thought to be a rare subspecies.
They could be blue bottles due to their similiarity to jellyfish and also similiar appearance.
The first appearance of a blue jellyfish is in "Tea at the Treedome".
The most prominent appearance of a blue jellyfish is in "Jellyfish Hunter." The blue jellyfish was known as "No Name". No Name helped SpongeBob stop Mr. Krabs from using jellyfish jelly for the Krabby Patties, in which they succeeded. In the end, No Name let itself be caught by SpongeBob and was renamed "Friend".
In the video game, Revenge of the Flying Dutchman, the player fights wild blue jellyfish. A boss is a big blue jellyfish with smaller ones protecting it. To defeat the boss, the player must catch the smaller blue ones with the fishing net, not touching them. While the player catches the jellyfish, they must hit the blue jellyfish with the bubbles to become the greatest jellyfisher ever. Blowing bubbles on the stingers is uneffective. Wild blue jellyfish also appear in the video game, Battle for Bikini Bottom. They only appear in certain areas of jellyfish fields, and they are faster than normal jellyfish and take two hits to defeat.