Dictionary / Vocabulary / 水を得た魚
みずをえたうお
someone who is in their element; fish that has found water
畑仕事をしているとき彼はまるで水を得た魚のようだ。
He's in his element when working on the farm.
テニスのことになると彼女は水を得た魚のようだ。
She is in her element when it comes to tennis.