How are sharks different from bony fish?

Sharks differ from bony fish in several fundamental anatomical and physiological ways:

• Skeleton: Sharks belong to the class Chondrichthyes and possess a skeleton composed of cartilage rather than true bone.12
• Buoyancy: Unlike most bony fish, sharks lack a swim bladder. Consequently, many species must swim perpetually to maintain their position in the water column and avoid sinking.23
• Gills: Sharks have five to seven external gill clefts on each side of the head. In contrast, bony fish have a single, movable bony covering over the gill chamber called an operculum.124
• Scales: Shark skin is covered in toothlike scales known as dermal denticles, which do not grow throughout the animal's life; instead, new scales form as the body expands.1
• Reproduction: While both groups exhibit diverse reproductive strategies, sharks and rays utilize a cloaca for waste and reproductive discharge, whereas bony fish typically have a separate urogenital opening. Many male sharks also possess specialized organs called claspers to facilitate internal fertilization.51