This document discusses the different types of scales found in fish. It defines fish scales as small, rigid plates that grow out of the skin. Scales come in various types depending on the fish, including cosmoid, ganoid, placoid, cycloid, and ctenoid scales. Each scale type has a distinct structure and provides different functions like protection from predators or parasites and aiding movement. Some fish lack scales and instead have alternatives like tough skin, bony plates, or prickles for protection. In summary, the document outlines the definition, functions, and major types of scales present in different groups of fish.

1. SCALES OF FISHES
Kiran Kanhurkar
Diversity in vertebrates
BSc zoology(hons)

2. Definition of scales
• A fish scale is a small rigid plate that grows out of the skin of a fish.
• The term scale derives from the Old French "escale", meaning a shell pod or husk.
• The type of scale will affect the behavior of fish
• Large, heavier scales providing more protection but restricting movement
• Smaller lighter scales offering more freedom of moment but less protection

3. Functions
• Protect the skin from attacks by
predators , parasites
• Allows fish to move easily in
vertical and horizontal direction
• Helps the shark swim more
quickly because their
streamlined shapes helps
decrease the friction of water
flowing along the sharks body

4. Types
1. COSMOID SCALE
2. GANOID SCALE
3. PLACOID SCALE
4.CYCLOID SCALES
5.CTENOID SCALES

6. COSMOID SCALES
• Found in extinct Crossopterygian and Dipnoid .
• Thin and enamel like external layer –
vitrodentine
• Dentine like middle layer- Cosmine
• and contains no. of branching tubules and
chambers
• Vasculaized bony substance-Isopedine

8. GANOID SCALES
• Found in ganoid fishes,
primitive actinopterygians
• outer layer –hard inorganic ,
enamel-like material –Ganoin
• Middle layer-Cosmine
• Innermost layer-lamellar bone ,
isopedine
• Shape - Rhomboid

9. E.g. gars (Lepisosteidae), and sturgeons (Acipenseridae).

10. PLACOID SCALES
• Found in elasmo branch
fishes only
• Structure- tooth like
• basal pate -embedded in
dermis
• Spiny projection –throughout
epidermis
• Spine having external
covering –vitrodentine (hard,
transparent material)
• Don’t overlap and give sand
paper like structure

11. E.g. sharks and rays

12. CYCLOID SCALE
• Found in teleostean fishes
• Thin, flexible, translucent plates,
rather circular in outline
• Thicken in center
• Concentric line of growth (can
determine age)
• Project diagonally in an imbricating
pattern

13. E.g. Salmon

14. CTENOID SCALES
• Found in modern higher
teleosteans
• Structure circular (like cycloid
scales)
• More firmly attached and
exposed free
• Hind parts which are not
overlapped

15. E.g. yellow perch

16. Fishes without scales
Fish without scales usually
evolve alternatives to the
protection scales can provide,
such as tough leathery skin or
bony plates.
Type of layers in place of scales
v smooth skin
v Though leathery skin
v body armor in the form of dermal
plates
v fine forked dermal prickles or
tubercles
v Exoskeleton-plates of ossified skin
fused
Seahorses have thin
skin stretched over
bony plates arranged in
rings
Mandarin fish lack scales
and protect themselves
with a layer of smelly and
bitter slime.

17. THANKYOU