Fish and shellfish are aquatic animals with diverse anatomy and biology. Fish have gills for breathing, fins for movement, and scales for protection, while shellfish include mollusks (like clams and oysters) and crustaceans (like crabs and shrimp) with hard exoskeletons. They exhibit varied reproductive strategies, from egg-laying to live birth. Their physiology is adapted to different aquatic environments, from freshwater to deep-sea habitats.