expression, noun
hanger-on; tagalong; clingy follower
Idiomatic expression literally meaning 'goldfish feces', used to describe a person who mindlessly follows someone around without contributing anything. Often used in a derogatory or humorous way.
彼はいつも部長の後ろを金魚のフンみたいについて歩いている。
He always follows the department head around like a shadow.
あの子、先輩の金魚のフンだよね。
That kid is such a tagalong to the senior, isn't she?
From the image of goldfish feces trailing behind the fish; the phrase is a vivid metaphor for a person who follows another around without purpose.