Types of Scales Types of Scales in Fishesin Fishes

ScaleScale

• A A scalescale is a small rigid plate that is a small rigid plate that grows out of an grows out of an animal's skin to 's skin to provide protection.provide protection.

• Generally classified as part of an Generally classified as part of an organism's integumentary system. organism's integumentary system.

•The study of scales is The study of scales is called called SquamatologySquamatology . .

Development & Development & LocationLocation

• Produced in the mesoderm.Produced in the mesoderm.• Located between the epidermis and the Located between the epidermis and the

underlying tissues. underlying tissues. • Genes responsible for the development of Genes responsible for the development of

scales in fish are same that result in hair scales in fish are same that result in hair and tooth development in mammals.and tooth development in mammals.

• They usually grow on a fish in They usually grow on a fish in overlapping plates, with the free end overlapping plates, with the free end of the scale pointed towards the tail.of the scale pointed towards the tail.

Functions of Functions of ScalesScales

• Provide external protection to its body as scales Provide external protection to its body as scales are tough & slippery.are tough & slippery.

• Help to protect a fish from scrapes, parasites Help to protect a fish from scrapes, parasites and other external injuries. and other external injuries.

• Because they are all attached at only one Because they are all attached at only one point, they provide flexibility so that the point, they provide flexibility so that the scales can slide over each other as the scales can slide over each other as the fish’s body bends while swimming. fish’s body bends while swimming.

Types of ScalesTypes of Scales• There are four different types of fish There are four different types of fish

scales.scales.1.1. Cosmoid scalesCosmoid scales2.2. Ganoid scalesGanoid scales3.3. Placoid scalesPlacoid scales4.4. Leptoid scalesLeptoid scales• Cycloid scales Cycloid scales • Ctenoid scalesCtenoid scales

• The structure and configuration of scales The structure and configuration of scales can be used to determine the species from can be used to determine the species from which they came.which they came.

• The type of scale will affect the behavior of The type of scale will affect the behavior of a fish:a fish:

• Larger, heavier scales providing more Larger, heavier scales providing more protection but restricting movement .protection but restricting movement .

• Smaller, lighter scales offering more Smaller, lighter scales offering more freedom of movement but less protection.freedom of movement but less protection.

1.Placoid Scales1.Placoid Scales

• Also called denticles, are similar in structure Also called denticles, are similar in structure to teeth. to teeth.

• Found on sharks, skates and rays.Found on sharks, skates and rays. • Formed of a rectangular base plate that is Formed of a rectangular base plate that is

embedded within the skin of the fish.embedded within the skin of the fish.

• The interior of the scale is a pulp that receives The interior of the scale is a pulp that receives blood from the fish's vascular system, while the blood from the fish's vascular system, while the outside is made of an enamel-like substance outside is made of an enamel-like substance called vitrodentine.called vitrodentine.

• Placoids have a sharp ridge down the Placoids have a sharp ridge down the center of the scale made of center of the scale made of vitrodentinevitrodentine ..

• The enamel ridge is called The enamel ridge is called an an ectodermal capectodermal cap , and this is important , and this is important because without this enamel cap the because without this enamel cap the sharks could not feed. sharks could not feed.

• Placoids do not grow with the fish. As a Placoids do not grow with the fish. As a shark gets larger it grows new scales to fill shark gets larger it grows new scales to fill in the gaps between the scales.  in the gaps between the scales. 

2. Cosmoid Scales2. Cosmoid Scales

• Very rare scale type, but no doubt common in Very rare scale type, but no doubt common in extinct species extinct species CrossopterygiansCrossopterygians , is the , is the cosmoid scale.  cosmoid scale. 

• Limited today to the primitive lobefins Limited today to the primitive lobefins and lungfish. and lungfish.

• Cosmoid scales evolved from placoid scales Cosmoid scales evolved from placoid scales fusing together. fusing together.

• This is because cosmoid scales have two base This is because cosmoid scales have two base plates and similar external spines composed of plates and similar external spines composed of vitrodentine.vitrodentine.

• Inner layer of the Inner layer of the scale is made scale is made of lamellar bone. of lamellar bone.

• On top of this lies a On top of this lies a layer of spongy layer of spongy or vascular bone and or vascular bone and then a layer then a layer of dentine-like of dentine-like material material called cosmine.called cosmine.

• These scales grow These scales grow along with the fish.along with the fish.

3. Ganoid Scales3. Ganoid Scales

• These can be found These can be found on gars, bichirs and on gars, bichirs and reed fishes. reed fishes.

• Rare among modern Rare among modern fish.fish.

• They are flat, basal-They are flat, basal-looking scales.looking scales.

• What’s unusual about What’s unusual about these scales is that these scales is that they do not overlap they do not overlap but instead fit together but instead fit together like pieces of a jigsaw like pieces of a jigsaw puzzle. puzzle.

• They have a bony base layer similar to that of They have a bony base layer similar to that of cosmoid scales. Indeed, ganoid scales are cosmoid scales. Indeed, ganoid scales are modified cosmoid scales.modified cosmoid scales.

• However, they differ in that their outer layer is However, they differ in that their outer layer is made of an inorganic bone salt called ganoine made of an inorganic bone salt called ganoine and that they are diamond-shaped and and that they are diamond-shaped and interconnected.interconnected.

• Between ganoid scales are peg-and-socket Between ganoid scales are peg-and-socket joints that articulate.joints that articulate.

• They act like armor to form a nearly They act like armor to form a nearly impenetrable barrier to predators.impenetrable barrier to predators.

• They also grow with the fish, not only They also grow with the fish, not only in length, but in width and thickness in length, but in width and thickness as well.as well.

4. Leptoid scales4. Leptoid scales• Found on higher-order bony fish. Found on higher-order bony fish. • As they grow they add concentric layers. As they grow they add concentric layers. • The two types are often grouped The two types are often grouped

together simply as together simply as "bony-ridged""bony-ridged" scales.scales.

• They come in two forms:They come in two forms:

1.1. Cycloid ScalesCycloid Scales 2.2. Ctenoid ScalesCtenoid Scales

Cycloid ScalesCycloid Scales

• Cycloid and ctenoid Cycloid and ctenoid scales have different scales have different shapes but the same shapes but the same composition and composition and positioning.positioning.

• The vast majority of The vast majority of bony fish have cycloid, bony fish have cycloid, or round scales.or round scales.

• These have a smooth These have a smooth outer edge and are most outer edge and are most common on fish with soft common on fish with soft fin rays such fin rays such as salmon and carp. as salmon and carp.

• These have two basic parts; These have two basic parts;

1.1.The inner solid structure made The inner solid structure made out of bone. out of bone.

2.2.An outer collagen layer. An outer collagen layer.

• Scales are not Scales are not shed as the fish shed as the fish ages, but grow ages, but grow with the animal.with the animal.

• The result of this, The result of this, is that a fish can is that a fish can be aged by be aged by counting the counting the growth rings.growth rings.

• Herring and other groups of bony fish Herring and other groups of bony fish have large cycloid scales that fall off have large cycloid scales that fall off very easily. Skin structures that are very easily. Skin structures that are shed easily are known as shed easily are known as deciduous deciduous scalesscales ..

Ctenoid scalesCtenoid scales

• They have a toothed They have a toothed outer edge (exposed outer edge (exposed part), spiny or have part), spiny or have comb-like ridges.comb-like ridges.

• Usually found on fish Usually found on fish with spiny fin rays, with spiny fin rays, such such as as bassbass  and  and crappiecrappie ..

• These have tiny teeth-These have tiny teeth-like protrusions called like protrusions called ctenii, giving them a ctenii, giving them a rougher texture.rougher texture.

  Scute ScaleScute Scale• Another less common, type of scale is Another less common, type of scale is

the the scutescute , which is:, which is:• An external shield-like bony plate, orAn external shield-like bony plate, or• A modified, thickened scale that often A modified, thickened scale that often

is keeled or spiny.is keeled or spiny.

• Some fish, such as pinecone fish, are Some fish, such as pinecone fish, are completely or partially covered in completely or partially covered in scutes.scutes.

Scaleless FishScaleless Fish • Some groups of fish lack scales Some groups of fish lack scales

completely, including gobies and toadfish. completely, including gobies and toadfish. • Instead, these fish are covered in a Instead, these fish are covered in a

coating of slime which will protect the fish coating of slime which will protect the fish from injury and ectoparasites. from injury and ectoparasites.

• The slime layer may serve the added The slime layer may serve the added function of making them especially hard function of making them especially hard for a predator to grab hold of.for a predator to grab hold of.

ReferencesReferences• www.wikipedia.orgwww.wikipedia.org

• www.australianmuseum.netwww.australianmuseum.net

• www.newton.depwww.newton.dep

• www.ehow.comwww.ehow.com

• www.earthlife.netwww.earthlife.net

• web.mac.comweb.mac.com