The Jellyfish texture pack allows you to rename pufferfish, so that they become jellyfish instead. There are many colour variants available like pink, red, purple, blue, etc. To convert a pufferfish into a jellyfish, you have to rename it with a name tag or in a bucket of pufferfish. Here's some of the names that you can rename your pufferfish into :

Red Jellyfish
Orange Jellyfish
Yellow Jellyfish
Green Jellyfish
Mint Jellyfish
Blue Jellyfish
Dark Blue Jellyfish
Purple Jellyfish
Hot Pink Jellyfish
Pink Jellyfish

Take a look at the screenshots to see what you can expect from this pack. Optifine is needed for this pack to work properly. Download links are given below. Read the installation instructions carefully.

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Jellyfish Texture Pack