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Mad Doctor Fish (マッドドクターフィッシュ, Maddo Dokutā Fisshu) are mysterious beings and part of the Monster Association. They live in a sort of symbiotic relationship with Evil Natural Water.[1]


The Mad Doctor Fish's appearances are based on red garras (also known as doctor fish), but they have larger jaws and sharper teeth that bear a resemblance to carnivorous piranhas. They also appear to possess an unusual six eyes.


Human Monster SagaEdit

Monster Association ArcEdit

The Mad Doctor Fish are seen swimming in the fish tank containing Evil Natural Water. A monster breaks the tank holding Evil Natural Water, releasing it as well as the fishes, to attack Atomic Samurai's Disciples. They devour the monster that released them, and Evil Natural Water then launches them at Iaian, but he easily slices them up.[2]

More Mad Doctor Fish appear when Evil Natural Water attacks Child Emperor, again launching them at its target. They chew up some of Child Emperor's backpack's arms and weapons, but he manages to dispose of most of them.[3]

After absorbing Sludge Jellyfish, the Mad Doctor Fish seem to have died from the oil in the water, and Evil Natural Water expels them.[4]

Abilities and PowersEdit

Mad Doctor Fish Chew

Mad Doctor Fish devour a monster in mere seconds.

Because their collective threat level is Tiger, it can be implied that the Mad Doctor Fish are not extremely powerful. However, they still act as an effective means for Evil Natural Water to conduct long-ranged attacks.

Physical AbilitiesEdit

Powerful Bite: Mad Doctor Fish have a strong bite that can easily pierce the flesh of other mysterious beings. They are able to completely devour weaker and wounded opponents in seconds, and could even chew through Child Emperor's metal weapons to break them.

Battles Edit

Participants Chapter(s) Episode(s) Result
Mad Doctor Fish vs. Iaian 114 None Loss
Mad Doctor Fish vs. Child Emperor 121 None Loss


  • They are the only monsters in the series so far to live in symbiosis with another.


  1. One-Punch Man Manga; Chapter 121, page 16
  2. One-Punch Man Manga; Chapter 114
  3. One-Punch Man Manga; Chapter 121
  4. One-Punch Man Manga; Chapter 122


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