Dr. Bibhuti Dutta SinghP. G. Department of Zoology

Dayanand Anglo Vedic Post Graduate

(D.A.V.P.G.) College, Siwan ,

Jai Prakash University, Chapra (Saran)

Bihar – 841301

Email: bibhuti.zoology@gmail.com

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STUDY MATERIAL

B.Sc. PART 2nd

PAPER -3rd

SUBJECT- ZOOLOGY

CLASS - FISHES

TOPIC

SCALES IN FISHES

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INTRODUCTION

(1) The study of fish is known as ICHTHYLOGY.

(2) The study of scales is called SQUAMATOLOGY.

(3) A scale is small rigid plate that grows out of an animals skin

to provide protection. Generally classified as part of an

organisms integumentary system.

(4) In many vertebrates, the exoskeletal covering of body is

made of two types of scales:

(A) Epidermal Scales

(B) Dermal Scales

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(A)Epidermal Scales- Epidermal scales are cornified

derivatives of the Malpighian layer of epidermis. They are

well developed in terrestrial vertebrates such as Reptiles,

Birds and Mammals.

(B) Dermal scales- Dermal Scales are mesenchymal in origin

and especially developed in the fishes. They are small, thin,

cornified, calcareous or bony plates which fit closey together

or overlap. Scales are usually found covering entire body

surface, but in some fishes like- Chimaerans, Polydon and

Acipenser ,the scales are present in some localized areas.

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TYPES OF SCALES

The following types of scales are found in living and

extinct fishes:

(1) Cosmoid Scales

(2) Placoid Scales

(3) Ganoid Scales

(4) Cycloid Scales

(5) Ctenoid Scales

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(1). COSMOID SCALES

These do not occur in living fishes. These were characteristic of

certain ostracoderms, placoderms, and extinct sarcopterygians (lobe

finned fishes and lung fishes).

These consisted of 4 distinct layers :

(A)Outermost thin enamel-like ganoine,

(B)Thick dentine-like cosmine,

(c) Spongy bone and

(D) Innermost compact bone.

Example: Extinct Crossopterygii and Dipnoi.

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FIG: Cosmoid Scale

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(2). PLACOID SCALES

(1) Also called denticles. These are characteristic of

elasmobranch fishes only. Each placoid scale consists of

a backwardly directed spine arising from a rounded or

rhomboidal basal plate embedded in dermis.

(2) Spine is made of enamel-like and basal plate of

dentine-like bony material. A pulp cavity inside spine

opens through basal plate.

(3) Placoid scales are closely set together in skin giving

it a sandpaper like quality.

Example. Scoliodon, Shark, Skates and Rays.

(Cartilaginous fishes)

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Fig: Dogfish (Scoliodon sorrakowah)

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Fig: Shark fish

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FIG: Placoid Scale Wih Dorsal and Ventral view

(3 ). GANOID SCALES

(1) Ganoid or rhomboid scales are thick, usually rhomboid or diamond-

shaped plates closely fitted side by side, like tiles, providing a bony

armour to the fish.

(2) In some cases they may overlap. Ganoid scales are characteristic of

chondrosteans (Polypterus, Acipencer) and holosteans (Leipidosteus) so

that these are often called ganoid fishes.

Polypterus has palaeoniscoid ganoid scales composed of 3 layers :

(A)outer enamel-like ganoine,

(B) Middle dentine-like cosmine and

(C)Inner bony isopedine.

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Lepidosteus has lepidosteoid ganoid scales with only two layers :

(A)Outer ganoine and

(B) Inner isopedine.

Example: Chondrosteans (Polypterus, Acipencer)

Holosteans (Lepidosteus), Bowfin(Amia calva)

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FIG: Ganoid Scale

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FIG: Polypterus (Polypterus bichir)

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FIG:Bowfin (Amia calva)

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(4). CYCLOID SCALES

(1)Cycloid scales are thin flexible translucent plates, rather

circular in outline, thicker in the centre and marked with

several concentric lines of growth which can be used for

determining the age of the fish.

(2) They are composed of a thin upper layer of bone and a

lower layer of fibrous connective tissue. They overlap each

other, each scale embedded in a small pocket of dermis.

Example: Lung fishes, Surviving Dipnoans some Holosteans

(Amia) and the Lower Teleosteans such as Carps, Cods etc.

!

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FIG :Cycloid Scale

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(5). CTENOID SCALES

(1) These are characteristic of modern higher teleosteans such

as perch, sunfish, etc. In form, structure and arrangement they

are similar to cycloid scales.

(2) They are more firmly attached and their exposed free hind

parts which are not overlapped, bear numerous small comblike

teeth or spines. Intermediate types between cycloid and ctenoid

scales also occur.

(3) Certain fishes, such as flounders, may bear both types,

ctenoid scales dorsally and cycloid ventrally.

Example: Higher bony fishes, Perches and bony Sunfishes.

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FIG: Perch fish (Perca fluviatilis)

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FIG: Green Sunfish (Lepomis cyanellus)

fish

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FIG:Ctenoid scale

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MODIFICATIONS OF SCALES(1) Some fishes are totally scaleless or naked, such as Torpedo (Electric ray) and Catfishes. In

Eels, they are minute and deeply embedded in dermis. In some fishes (Chimaeras) they

become localized.

(2) In Globe fish (Tetrodon) and Porcupine fish (Diodon), they develop into' large protective

spines making it difficult to be swallowed.

In trunk fish (Ostracion) they form a complete bony box. In sturgeon (Acipenser) stout bony

plates or scutes form a bony armour.

Shark teeth are modifie large placoid scales.

(3) Sting (Barb) of a sting ray is a modified placoid scale. The lateral, teeth on the elongated

rostrum of sawfish (Pristis) are formed by placoid scales. In Basking Shark (Cetorhinus)

myriads of placoid scales become gill rakers.

(4) In Hippocampus (Sea horse) and Syngnathus (Pipe fish) the scales become fused to form a

protective bony ring around the body.

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Fig: Electric fish (Torpido torpido)

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FIG: Cat Fish

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USES OF OF SCALES

(1)Scales form a protective covering of exoskeleton on

the body. Scales grow throughout life in size with the

fish.

(2)Growth results in concentric lines which make age

determination possible in Salmon, Trout, Bass and

several other species. For every species, its scale

pattern is rather constant.

(3)Thus arrangement, number, form and structure of

scales play important role in identification and

classification of fish species.

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CONCLUSIONAfter going through the above discussion, the fish

scale is a small rigid plate that grows out of the

skin of a fish. 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

hdrodynamic advantages. So fish scales are part

of fish’s integumentary system ,and are produced

from the mesoderm layer of the dermis.

d

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Reference Books

A HAND BOOK OF FISH BIOLOGY AND FISHERIES BY PAUL J.

B. HART AND JOHN D. REYNOLDS

A TEXT BOOK OF FISH BIOLOGY AND FISHERIES BY S.S.

KHANA, H.R.SINGH

MODERN TEXT BOOK OF VERTEBRATES (ANIMAL DIVERSITY)

BY R.L. KOTPAL

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THANK YOU

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