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Scale of fishes

Scales are an important part of the exoskeleton of most fish species. There are several different types of scales that evolved over time, including placoid, cycloid, ctenoid, cosmoid, and ganoid scales. Placoid scales are found in sharks and resemble teeth, while cycloid and ctenoid scales are thin and circular or spiny and found in bony fish. Scales provide protection and can be used to determine age and growth rates in fish, as well as provide information about extinct fish species and the diets of predatory animals.

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Scale of FishesScale of Fishes Presented byPresented by Balwant SinghBalwant Singh Shivangi ThipathiShivangi Thipathi Babasaheb Bhimrao Ambedkar UniversityBabasaheb Bhimrao Ambedkar University Lucknow-226025 INDIALucknow-226025 INDIA
SCALES IN FISHESSCALES IN FISHES
CONTENTCONTENT  INTRODUCTIONINTRODUCTION  TYPES OF SCALESTYPES OF SCALES  USES OF SCALESUSES OF SCALES
INTRODUCTIONINTRODUCTION  The scales and dentictes of various kinds areThe scales and dentictes of various kinds are the most complex derivatives of thethe most complex derivatives of the integument.integument.  Scales form an important exoskeleton of mostScales form an important exoskeleton of most species of fishes,except cat fishes andspecies of fishes,except cat fishes and Acipenser (only few regions of the body).Acipenser (only few regions of the body).  They are derived from the mesenchymal cellsThey are derived from the mesenchymal cells of dermis.Dermis lies under the epidermis.of dermis.Dermis lies under the epidermis.
Evolution of scalesEvolution of scales  In cyclostomes the dermal bones are not found,In cyclostomes the dermal bones are not found, but the collagen fibre increase in amount andbut the collagen fibre increase in amount and become densly packed.become densly packed.  In ostracodermis the dermal bones areIn ostracodermis the dermal bones are enormously developed and disposed in the formenormously developed and disposed in the form of broad plates covering the entire body.of broad plates covering the entire body.  The scales formed in the course of evolutionThe scales formed in the course of evolution from primitive to modern types are of variousfrom primitive to modern types are of various types and called thetypes and called the cosmoid,ganoid,placoid.cycloid,and the ctenoidcosmoid,ganoid,placoid.cycloid,and the ctenoid scales.scales.
Types of scalesTypes of scales On the basis of their origin scales are two types-On the basis of their origin scales are two types-  Placoid scales-which develop from epidermisPlacoid scales-which develop from epidermis as well as dermis,and are characteristicallyas well as dermis,and are characteristically found in the elasmobranchs.found in the elasmobranchs.  Non-placoid scales-which develops from theNon-placoid scales-which develops from the dermis only,as the scales of teleosteandermis only,as the scales of teleostean fishes.The non-placoid scales can be offishes.The non-placoid scales can be of cosmoid,ganoid,cycloid or ctenoid.cosmoid,ganoid,cycloid or ctenoid.
Placoid scalePlacoid scale  Placoid scales or dermal denticles are found in thePlacoid scales or dermal denticles are found in the elasmobranchs.elasmobranchs.  They have dentine laid down by osteocyte cells andThey have dentine laid down by osteocyte cells and pulp,cavity,ramified in a manner similar to thepulp,cavity,ramified in a manner similar to the teeth of vertebrates.teeth of vertebrates.  Each scale consists of a basal plate and a spineEach scale consists of a basal plate and a spine projecting out,giving a rough surface to the skin.projecting out,giving a rough surface to the skin.  The basal plate is formed of a substance resemblingThe basal plate is formed of a substance resembling the cement of teeth,secreted by the dermis.the cement of teeth,secreted by the dermis.  The spine develops from the malpighian layer ofThe spine develops from the malpighian layer of the epidermis.the epidermis.
 The placoid scales do not overlap each other andThe placoid scales do not overlap each other and are closely set in the skin.are closely set in the skin.  The size of placoid scalesvary on different parts ofThe size of placoid scalesvary on different parts of body.these are usually large large on the snout andbody.these are usually large large on the snout and on the mid-dorsal line of the body.on the mid-dorsal line of the body.  In saw fish(pristis) the large spines (teeth)on theIn saw fish(pristis) the large spines (teeth)on the saw are the modified placoid scales.saw are the modified placoid scales. Cont……..
Cycloid scalesCycloid scales  These scales are thin,transparent,roughly roundedThese scales are thin,transparent,roughly rounded in shape.in shape.  The scales shows alternating ridges and grooves.The scales shows alternating ridges and grooves.  The cycloid scales are mostly found in major carps(The cycloid scales are mostly found in major carps( eg. Labeo rohita,cirrhinus mrigala,Catla catla)areeg. Labeo rohita,cirrhinus mrigala,Catla catla)are project diagonally in an imbricatingproject diagonally in an imbricating pattern,forming a protective covering over thepattern,forming a protective covering over the body.body.
Ctenoid scalesCtenoid scales  These are derived from cycloid scalesThese are derived from cycloid scales and are confined to spiny rayedand are confined to spiny rayed teleosts.teleosts.  The ctenoid scales is also thin andThe ctenoid scales is also thin and circular like cycloid,but has a margincircular like cycloid,but has a margin and several distinct spines are presentand several distinct spines are present on the posterior part of the body.on the posterior part of the body.  These scales are found in the largeThese scales are found in the large number of perciform fishes andnumber of perciform fishes and develop from the dermis.develop from the dermis.
Cosmoid scaleCosmoid scale  The cosmoid scales were found in the extinctThe cosmoid scales were found in the extinct crossopterygii and dipnoicrossopterygii and dipnoi  They are not present in living fish.They are not present in living fish.  In the living crossopterygii (latimeria) and in livingIn the living crossopterygii (latimeria) and in living dipnoi they have become thin and modified to lookdipnoi they have become thin and modified to look like cycloid scales.like cycloid scales.
Ganoid scaleGanoid scale  These are heavy scales of various forms and shapesThese are heavy scales of various forms and shapes and are found in the primitive actinopterygianand are found in the primitive actinopterygian fishes as Acipenser, Lepidosteus and Amia whichfishes as Acipenser, Lepidosteus and Amia which are also called ganoid fishes.are also called ganoid fishes.  In lepidosteus these scales are hard rhombic plateIn lepidosteus these scales are hard rhombic plate like fitting edge to edge.like fitting edge to edge.  In amia ,the scales are soft and have thin ganoidIn amia ,the scales are soft and have thin ganoid layer.layer.
Uses of scalesUses of scales  The scales of fishes have become modified inThe scales of fishes have become modified in various way, mainly to provide protection.various way, mainly to provide protection.  In the Sharks, scales become modified to formIn the Sharks, scales become modified to form teeth in the jaws to help in catching prey.teeth in the jaws to help in catching prey.  Scales are used in circulating the age of fishesScales are used in circulating the age of fishes and rate of their growth.and rate of their growth.  Scales provide important information aboutScales provide important information about extinct fishes and are useful in identifying foodextinct fishes and are useful in identifying food habits of piscivorous animals.habits of piscivorous animals. ThankYouThankYou