In Minecraft, nautiluses are attracted to and tamed with pufferfish. They also eat other kinds of fish for healing and breeding.
Main food
Nautiluses use pufferfish as their key food. Feeding a nautilus pufferfish lets you tame it, and pufferfish are also used to put two nautiluses into “love mode” so they can breed.
Other fish
For general feeding and breeding, nautiluses can eat any regular fish item or any fish-in-a-bucket item. This includes options like cod, salmon, tropical fish, and their bucket variants.
