Fish: what's useful with that ?

[Koub]

Eat them when injured, they'll heal you.
[Koub] Moved to gameplay help

[valneq]

In order to eat fish, take them in your hand and then left click. I'm not sure this is explained well in the item description.

[BlueTemplar]

Fish are OP.
Plz fix by making them less tasty !

[Serenity]

They are really useful in early and mid game combat and can often save your life.

Some people also use the fish signal in combinators :p

[Ranger_Aurelien]

They're also required for the secret Achievement "So long and thanks for all the fish". (I kid you not)

I won't spoil it for you but with the 0.17 changes that is my group's fav way to celebrate getting to that technology level...

[MicFac]

Fish are a great way to heal while in combat. You don't start naturally regenerating health until a few seconds after you stopped taking damage, but you can eat fish to instantly get back a big amount of health. To eat fish, you need to have it on your cursor (left click the item in your inventory or hotbar to pick it up) and then just left click.