1. Zoology For us S uper class Pisces The Scales

2. Introduction of Scales Origin of Scales Types of Scales Structure of Scales Functions of Scales Topic Cover…

3. S uper class Pisces The Scales: Structure of Skin

5. S uper class Pisces The Scales: Origin

6. S uper class Pisces The Scales: Introduction ⦿ A fish scale is a small rigid plate that grows out of the skin of a fish.skin ⦿ The skin of most 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.scalescamouflagereflectioncolouration ⦿ The term scale derives from the Old French "escale", meaning a shell pod or husk.Old French ⦿ 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.shrimpfishesboxfisheseelsanglerfishes

7. S uper class Pisces The Scales: Types

8. ⦿ The morphology of a scale can be used to identify the species of fish it came from.morphology ⦿ 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. bony fishessalmoncarpperchsturgeonsgars ⦿ Cartilaginous fishes (sharks and rays) are covered with placoid scales. Cartilaginous fishessharksrays ⦿ Some species are covered instead by scutes, and others have no outer covering on part or all of the skin.scutes S uper class Pisces The Scales: Introduction

9. S uper class Pisces The Scales: Cartilaginous & Bony fishes

10. ⦿ Fish scales are part of the fish's integumentary system, and are produced from the mesoderm layer of the dermis, which distinguishes them from reptile scales. integumentary systemmesodermdermisreptile scales ⦿ The same genes involved in tooth and hair development in mammals are also involved in scale development.genesmammals ⦿ The placoid scales of cartilaginous fishes are also called dermal denticles and are structurally homologous with vertebrate teeth.homologous ⦿ It has been suggested that the scales of bony fishes are similar in structure to teeth, but they probably originate from different tissue. ⦿ Most fish are also covered in a layer of mucus or slime which can protect against pathogens such as bacteria, fungi, and viruses, and reduce surface resistance when the fish swims.mucus S uper class Pisces The Scales: Introduction

11. S uper class Pisces The Scales: Types

13. ⦿ Placoid (pointed, tooth-shaped) scales are found in the cartilaginous fishes: sharks, rays.cartilaginous fishessharksrays ⦿ They are also called dermal denticles. ⦿ Placoid scales are structurally homologous with vertebrate teeth ("denticle" translates to "small tooth"), having a central pulp cavity supplied with blood vessels, surrounded by a conical layer of dentine, all of which sits on top of a rectangular basal plate that rests on the dermis.homologousvertebrateteethpulp cavityblood vesselsdentinedermis ⦿ The outermost layer is composed of vitrodentine, a largely inorganic enamel-like substance.vitrodentineenamel ⦿ Placoid scales cannot grow in size, but rather more scales are added as the fish increases in size. ⦿ Similar scales can also be found under the head of the denticle herring. The amount of scale coverage is much less in rays.denticle herring Placoid scales

14. S uper class Pisces The Scales: Types ⦿ Ganoid scales are found in the sturgeons, paddlefishes, gars, bowfin, and bichirs.sturgeonspaddlefishesgarsbowfinbichirs ⦿ They are derived from cosmoid scales and often have serrated edges. ⦿ They are covered with a layer of hard enamel-like dentine in the place of cosmine, and a layer of inorganic bone salt called ganoine in place of vitrodentine.dentinecosmineganoinevitrodentine ⦿ Ganoine is a characteristic component of ganoid scales. ⦿ It is a glassy, often multi-layered mineralized tissue that covers the scales, as well as the cranial bones and fin rays in some non-teleost ray-finned fishes, such as gars, bichirs, and coelacanths.tissuecranialfin raysray-finned fishesgarsbichirscoelacanths Ganoid scales

15. S uper class Pisces The Scales: Types ⦿ It is composed of rod-like apatite crystallites.apatite ⦿ Ganoine is an ancient feature of ray-finned fishes, being found for example on the scales of stem group actinopteryigian Cheirolepis.stem groupCheirolepis ⦿ While often considered a synapomorphic character of ray-finned fishes, ganoine or ganoine- like tissues are also found on the extinct acanthodii. synapomorphic characteracanthodii ⦿ It has been suggested ganoine is homologous to tooth enamel in vertebrates or even considered a type of enamel.homologoustooth enamel Ganoid scales

16. S uper class Pisces The Scales: Types ⦿ Cycloid (circular) scales have a smooth texture and are uniform, with a smooth outer edge or margin. ⦿ They are most common on fish with soft fin rays, such as salmon and carpsalmoncarp Cycloid scales

17. S uper class Pisces The Scales: Types ⦿ Ctenoid (toothed) scales are like cycloid scales, except they have small teeth or spinules called ctenii along their outer or posterior edges.spinules ⦿ Because of these teeth, the scales have a rough texture. ⦿ They are usually found on fishes with spiny fin rays, such as the perch-like fishes.perch-like ⦿ These scales contain almost no bone, being composed of a surface layer containing hydroxyapatite and calcium carbonate and a deeper layer composed mostly of collagen.hydroxyapatitecalcium carbonatecollagen ⦿ The enamel of the other scale types is reduced to superficial ridges and ctenii Ctenoid scales

18. S uper class Pisces The Scales: Types

19. S uper class Pisces The Scales: Function

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