why is the poet compared to a fish
The poet is compared to a fish because the mirror is taken to be a lake and the woman seems to be a creature which has risen from the lake in her old age because her older visage is unrecognizable even for herself. She seems to belong to some magical land within the mirror as she cannot accept the fact of the truth that she has grown old.
The woman is compared to a fish because on looking from above the surface, a fish inside water appears ugly and shapeless. However, if one goes inside the water and looks at it, it looks beautiful. Similarly, the woman looks at her outward appearance in the mirror which is unattractive and hard-featured. But on delving deeper, there is another facet to her personality, that is her inner beauty, beauty that is not skin deep. The poetess wants to emphasise that one should look out for innate qualities rather than outwardly appearances.