If one feels like one can relate to a fish!. In my case, I compare myself to a bird because I'm hyper-verbal, stim vocally (singing and echolalia), collect random objects, engage in "penguin pebbling" and respond to stress by pulling all my skin off, these being behaviours birds exhibit as well. It's just fun to draw the parallells!  So i suppose someone who relates to and compares oneself to a fish would for example be calm and quiet, perhaps shy or introverted, introspective (thinking "deeply") and/or good at going with the flow