Conversely, we say, als een vis in het water = "like a fish in (the) water", which means "in his natural habitat = in an environment where he/she functions very well".

Or acqua in bocca and muto come un pesce. There are too much expressions.

@Cerberus We say the same.

Good.

Come un pesce in acqua.

"Water in one's mouth"...what does that mean? "Mute like a fish" makes sense. Not sure we have that.

@Cerberus It means "don't speak."

When you are drinking, and you have water in your mouth, you cannot speak. :)

Ah OK haha.

It is usually said as Mi raccomando, acqua in bocca.

Ah, I like those fish expressions. "Like a fish out of water" is pretty common, and I think I've heard "like a fish in water" before. It makes me think of "like a fish [or duck] to water"

Ahh yes.

I think that is more about the process of starting with a certain activity?

Yeah, that sounds right.

Right.

How about like a snail in a rose bed?

I'm not getting into like a snail on a boat...

Hee.