From The Wajas Wiki

Gills are a type of Potion Mutation. They can be permanently added to your waja by using a Slime Potion. This mutation cannot be colored and so always appears red in color.

Mutation Appearance

GillsAerial.png GillsAfrican.png {{{arctic}}} GillsBane.png {{{breedless}}} GillsCorsie.png GillsDivine.png GillsEarth.png GillsEgyptian.png GillsFire.png GillsForest.png GillsImp.png GillsNormal.png GillsPlushie.png GillsSpitz.png GillsTempest.png GillsWater.png