Scale of fishes

1. 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

2. SCALES IN FISHESSCALES IN FISHES

3. CONTENTCONTENT
 INTRODUCTIONINTRODUCTION
 TYPES OF SCALESTYPES OF SCALES
 USES OF SCALESUSES OF SCALES

4. 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.

5. 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.

6. 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.

8. 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.

9.  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……..

10. 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.

11. 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.

12. 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.

13. 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.

14. 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.
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