Fish scale

Fish Scale

Fish scales

Fish scales are small rigid plates that grow out of the skin of a fish. They provide protection and play a role in locomotion. Fish scales are part of the fish's integumentary system, which includes the skin and its derivatives.

Types of Fish Scales

Fish scales come in several different types, each with unique characteristics and functions. The main types of fish scales are:

Placoid Scales

Placoid scales, also known as dermal denticles, are found in cartilaginous fish such as sharks and rays. These scales are similar in structure to teeth, with a central pulp cavity surrounded by dentine and an outer layer of enamel. Placoid scales reduce drag and turbulence, allowing the fish to swim more efficiently.

Cosmoid Scales

Cosmoid scales are found in some extinct fish and are believed to have evolved from placoid scales. They consist of a layer of cosmine (a form of dentine) and a layer of vitrodentine (similar to enamel). Modern fish do not have cosmoid scales, but they were present in ancient lobe-finned fishes.

Ganoid Scales

Ganoid scales

Ganoid scales are found in fish such as gars and bichirs. These scales are diamond-shaped and have a shiny, enamel-like surface called ganoine. Ganoid scales are thick and provide excellent protection.

Cycloid and Ctenoid Scales

Cycloid and ctenoid scales are found in most bony fish. Cycloid scales are smooth and rounded, while ctenoid scales have tiny teeth on their posterior edges. These scales are thin and flexible, allowing for greater mobility.

Structure and Composition

Fish scales are composed of a bony layer covered by a layer of skin. The bony layer is made of calcium phosphate and collagen fibers, providing strength and flexibility. The outer layer of the scale is covered by a thin layer of skin that secretes mucus, reducing friction and protecting against infection.

Function

Fish scales serve several functions:

• Protection: Scales protect fish from predators, parasites, and physical damage.
• Locomotion: The streamlined shape of scales reduces water resistance, aiding in efficient swimming.
• Camouflage: Scales can reflect light, helping fish blend into their environment.

Evolutionary Significance

Thelodont denticles

Fish scales have evolved over millions of years, adapting to different environments and ecological niches. The diversity of scale types reflects the evolutionary pressures faced by different fish species.

Related Pages

• Fish anatomy
• Integumentary system
• Evolution of fish

Gallery

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  Fish scale of a Barramundi

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  Coelacanth scales

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  Spotted Gar scales

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  Ganoine layers in Alligator Gar scales

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  Amblypterus macropterus scales