The lower half is fish.... but the top half has boobs!
@Retired_Engineer: Don't forget about the old Bobby Bare "Mermaid" song:
Then one day she swam away and I sang to the clams and whalesI missed her fins and her seaweed hair and the silvery shine of her scalesThen her sister she swam by and set my heart awhirlCause her upper part was an ugly fish but the bottom part was a girl. 4951