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Jun 06, 2024 · Yin Yin Wong



Fig. 2: The cycloid scale of a carp has a smooth outer edge (top edge)

Fish Scale
A fish scale is a small rigid plate that grows out of the skin of a fish. The skin of most jawed fishes is covered with these protective scales, which can also provide effective camouflage through the use of reflection and colouration, as well as possible hydrodynamic advantages. The term scale derives from the Old French escale, meaning a shell pod or husk.

Scales vary enormously in size, shape, structure, and extent, ranging from strong and rigid armour plates in fishes such as shrimpfishes and boxfishes, to microscopic or absent in fishes such as eels and anglerfishes. The morphology of a scale can be used to identify the species of fish it came from. Scales originated within the jawless ostracoderms, ancestors to all jawed fishes today. Most bony fishes are covered with the cycloid scales of salmon and carp, or the ctenoid scales of perch, or the ganoid scales of sturgeons and gars. Cartilaginous fishes (sharks and rays) are covered with placoid scales. Some species are covered instead by scutes, and others have no outer covering on part or all of the skin.

Fig. 3. The cellular layers of the skin consists of an epidermis, dermis, and hypodermis. The epidermis (outermost cellular layer) is very thin, usually only 6 to 8 cells thick and contains unicellular mucous glands with a network of very small capillaries. The dermis (middle layer) contains the scales, the scale forming cells, pigment, blood vessels, and nerves. The hypodermis is a vascularized fatty layer between the epidermis and the muscle or bone beneath. It is the interface between the skin and the rest of the body.