This was sent in to the NYT Metro Diary and has been confirmed by the NYCT:
I had just given up my rat search when I saw some movement out of the corner of my eye. It wasn’t a rat, but a tiny fish swimming up and down the tracks.
I looked around excitedly for someone to share it with. Finally a subway worker came along, whom I quickly grabbed and announced, “There’s a fish!” I figured he would tell me I was imagining it, but he smiled and said: “I know. It’s been there for two weeks.”
I went back a few days later, hoping to see the fish again. Amazingly, there he was in the exact same spot — about the size of my pointer finger, swimming around, dining on subway trash and probably wondering where his subway fish friends were.
A fish tale on 14th Street.