How to tame a nautilus and get nautilus armor in Minecraft
feed two tamed adults any fish or any bucket of fish (Cod, Salmon, Tropical Fish, Pufferfish, raw or cooked).

The Tropical Fish cannot be cooked and restores only 1 hunger point; it comes in thousands of pattern and color mixes. Fish come from fishing with a rod or from killing fish in the water. All fish work the same; the Cooked Cod page explains them.
This item has no crafting recipe.
feed two tamed adults any fish or any bucket of fish (Cod, Salmon, Tropical Fish, Pufferfish, raw or cooked).
It is dropped by Tropical Fish, Elder Guardian and Guardian. Bought by Villager: Fisherman (Expert). Fishing: Fishing Rod.
It is a fish to eat or to use with animals and potions. Animals that eat it: Nautilus and Wolf.
1 hunger points (0.5 drumsticks) and 0.2 saturation.
A Balanced Diet (Eat everything that is edible, even if it's not good for you); Fishy Business (Catch a fish).