Types of ScalesTypes of Scales
in Fishesin Fishes
• A A scalescale is a small rigid plate thatis 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 anGenerally classified as part of an
organism's integumentary system.organism's integumentary system.
•The study of scales isThe study of scales is
called called SquamatologySquamatology ..
Development &Development &
• Produced in the mesoderm.Produced in the mesoderm.
• Located between the epidermis and theLocated between the epidermis and the
underlying tissues.underlying tissues.
• Genes responsible for the development ofGenes responsible for the development of
scales in fish are same that result in hairscales in fish are same that result in hair
and tooth development in mammals.and tooth development in mammals.
• They usually grow on a fish inThey usually grow on a fish in
overlapping plates, with the free endoverlapping plates, with the free end
of the scale pointed towards the tail.of the scale pointed towards the tail.
Functions ofFunctions of
• Provide external protection to its body as scalesProvide external protection to its body as scales
are tough & slippery.are tough & slippery.
• Help to protect a fish from scrapes, parasitesHelp to protect a fish from scrapes, parasites
and other external injuries.and other external injuries.
• Because they are all attached at only oneBecause they are all attached at only one
point, they provide flexibility so that thepoint, they provide flexibility so that the
scales can slide over each other as thescales 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 fishThere are four different types of fish
1.1. Cosmoid scalesCosmoid scales
2.2. Ganoid scalesGanoid scales
3.3. Placoid scalesPlacoid scales
4.4. Leptoid scalesLeptoid scales
• Cycloid scalesCycloid scales
• Ctenoid scalesCtenoid scales
• The structure and configuration of scalesThe structure and configuration of scales
can be used to determine the species fromcan be used to determine the species from
which they came.which they came.
• The type of scale will affect the behavior ofThe type of scale will affect the behavior of
a fish:a fish:
• Larger, heavier scales providing moreLarger, heavier scales providing more
protection but restricting movement .protection but restricting movement .
• Smaller, lighter scales offering moreSmaller, lighter scales offering more
freedom of movement but less protection.freedom of movement but less protection.
• Also called denticles, are similar in structureAlso 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 isFormed 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 receivesThe interior of the scale is a pulp that receives
blood from the fish's vascular system, while theblood from the fish's vascular system, while the
outside is made of an enamel-like substanceoutside is made of an enamel-like substance
called vitrodentine.called vitrodentine.
• Placoids have a sharp ridge down thePlacoids have a sharp ridge down the
center of the scale made ofcenter of the scale made of vitrodentinevitrodentine..
• The enamel ridge is calledThe enamel ridge is called
an an ectodermal capectodermal cap , and this is important, and this is important
because without this enamel cap thebecause without this enamel cap the
sharks could not feed.sharks could not feed.
• Placoids do not grow with the fish. As aPlacoids do not grow with the fish. As a
shark gets larger it grows new scales to fillshark gets larger it grows new scales to fill
in the gaps between the scales. in the gaps between the scales.
• Very rare scale type, but no doubt common inVery rare scale type, but no doubt common in
extinct speciesextinct species CrossopterygiansCrossopterygians , is the, is the
cosmoid scale. cosmoid scale.
• Limited today to the primitive lobefinsLimited today to the primitive lobefins
and lungfish.and lungfish.
• Cosmoid scales evolved from placoid scalesCosmoid scales evolved from placoid scales
fusing together.fusing together.
• This is because cosmoid scales have two baseThis is because cosmoid scales have two base
plates and similar external spines composed ofplates and similar external spines composed of
• Inner layer of theInner layer of the
scale is madescale is made
of lamellar bone.of lamellar bone.
• On top of this lies aOn top of this lies a
layer of spongylayer of spongy
or vascular bone andor vascular bone and
then a layerthen a layer
of dentine-likeof dentine-like
called cosmine.called cosmine.
• These scales growThese scales grow
along with the fish.along with the fish.
• These can be foundThese can be found
on gars, bichirs andon gars, bichirs and
reed fishes.reed fishes.
• Rare among modernRare among modern
• They are flat, basal-They are flat, basal-
looking scales.looking scales.
• What’s unusual aboutWhat’s unusual about
these scales is thatthese scales is that
they do not overlapthey do not overlap
but instead fit togetherbut instead fit together
like pieces of a jigsawlike pieces of a jigsaw
• They have a bony base layer similar to that ofThey have a bony base layer similar to that of
cosmoid scales. Indeed, ganoid scales arecosmoid scales. Indeed, ganoid scales are
modified cosmoid scales.modified cosmoid scales.
• However, they differ in that their outer layer isHowever, they differ in that their outer layer is
made of an inorganic bone salt called ganoinemade of an inorganic bone salt called ganoine
and that they are diamond-shaped andand that they are diamond-shaped and
• Between ganoid scales are peg-and-socketBetween ganoid scales are peg-and-socket
joints that articulate.joints that articulate.
• They act like armor to form a nearlyThey act like armor to form a nearly
impenetrable barrier to predators.impenetrable barrier to predators.
• They also grow with the fish, not onlyThey also grow with the fish, not only
in length, but in width and thicknessin 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 groupedThe two types are often grouped
together simply astogether simply as "bony-ridged""bony-ridged"
• They come in two forms:They come in two forms:
1.1. Cycloid ScalesCycloid Scales
2.2. Ctenoid ScalesCtenoid Scales
• Cycloid and ctenoidCycloid and ctenoid
scales have differentscales have different
shapes but the sameshapes but the same
composition andcomposition and
• The vast majority ofThe vast majority of
bony fish have cycloid,bony fish have cycloid,
or round scales.or round scales.
• These have a smoothThese have a smooth
outer edge and are mostouter edge and are most
common on fish with softcommon on fish with soft
fin rays suchfin 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 madeThe inner solid structure made
out of bone.out of bone.
2.2.An outer collagen layer.An outer collagen layer.
• Scales are notScales are not
shed as the fishshed as the fish
ages, but growages, but grow
with the animal.with the animal.
• The result of this,The result of this,
is that a fish canis that a fish can
be aged bybe aged by
counting thecounting the
growth rings.growth rings.
• Herring and other groups of bony fishHerring and other groups of bony fish
have large cycloid scales that fall offhave large cycloid scales that fall off
very easily. Skin structures that arevery easily. Skin structures that are
shed easily are known as shed easily are known as deciduousdeciduous
• They have a toothedThey have a toothed
outer edge (exposedouter edge (exposed
part), spiny or havepart), spiny or have
comb-like ridges.comb-like ridges.
• Usually found on fishUsually found on fish
with spiny fin rays,with spiny fin rays,
as as bassbass and and crappiecrappie..
• These have tiny teeth-These have tiny teeth-
like protrusions calledlike protrusions called
ctenii, giving them actenii, giving them a
rougher texture.rougher texture.
Scute ScaleScute Scale
• Another less common, type of scale isAnother 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 oftenA modified, thickened scale that often
is keeled or spiny.is keeled or spiny.
• Some fish, such as pinecone fish, areSome fish, such as pinecone fish, are
completely or partially covered incompletely or partially covered in
Scaleless FishScaleless Fish
• Some groups of fish lack scalesSome groups of fish lack scales
completely, including gobies and toadfish.completely, including gobies and toadfish.
• Instead, these fish are covered in aInstead, these fish are covered in a
coating of slime which will protect the fishcoating of slime which will protect the fish
from injury and ectoparasites.from injury and ectoparasites.
• The slime layer may serve the addedThe slime layer may serve the added
function of making them especially hardfunction of making them especially hard
for a predator to grab hold of.for a predator to grab hold of.