Bottom
鱼 — the indexing fish radical, the simplified form of
鳥-counterpart
魚. It puts
鳖 in the broad aquatic-creature family that includes proper fish (
鲤,
鲫,
鲨), shellfish, and reptiles classed with them. The softshell turtle isn't strictly a fish, but classical taxonomy grouped water-dwelling creatures together — the radical signals 'lives in fresh water.'