Fish Scales: Types, Functions and Uses

Fish scales are basically four types, including cycloid, ctenoid, placoid, and ganoid scales each with unique characteristics and purposes.

Fish scales are an essential feature of almost all fish species, serving a variety of functions such as protection, aiding in movement, and providing materials for human use.

Fish scales have also been used for various human applications throughout history, such as creating jewelry, artwork, and even traditional medicines.

In this article, we explore the different types of fish scales, their functions, and their industrial applications.

What is Fish Scale?

Fish scales are the small, flattened, and overlapping structures that cover the skin of fish. The size and arrangement of scales can be distinct features used in identifying different fish species.

Fish can have scales of various sizes and shapes depending on their species. Scales can range from tiny and almost invisible to large and prominent.

During the transition from late larvae to early fry stage, small scales begin to appear on the body of young fish.

Although the number of scales remains the same, their size increases as the fish grows older.

The growth rate and lifespan of the fish can be determined by studying the pattern of scale formation, as well as the transition to spawning.

Fish Scales Types

There are four main types of fish scales,

  1. Cycloid scales
  2. Ctenoid scales
  3. Ganoid scales
  4. Placoid scales

1. Cycloid Scales

Cycloid scales of fish

These scales are found on most modern bony fish. They are a type of fish scale that has a smooth, rounded edge. Cycloid scales are small, round scales that overlap like shingles on a roof.

They are characterized by their circular or oval shape and lack of spines or ridges along the edge.

Cycloid scales are typically thin and flexible, allowing for some degree of overlap between adjacent scales.

These scales provide fish with protection against predators, reduce water resistance during swimming, and assist with buoyancy control.

Several fish species have cycloid scales. Some examples of fish with cycloid scales include:

  1. Common Carp (Cyprinus carpio): Carp are known for their large cycloid scales, which can range in color from gold to bronze. These scales are often used in traditional Japanese koi breeding to achieve various color patterns.
  2. Trout (Various Species): Many species of trout, including rainbow trout and brown trout, have cycloid scales. These scales can vary in color and size depending on the specific trout species and habitat.
  3. Perch (Various Species): Perch, such as the European perch and yellow perch, are known for their small, overlapping cycloid scales. These scales can be quite colorful and contribute to the fish’s appearance.
  4. Bream (Various Species): Bream, like bluegill and pumpkinseed, also have cycloid scales. These scales are often iridescent and can display striking patterns.
  5. Crucian Carp (Carassius carassius): Crucian carp, a close relative of the common carp, have cycloid scales and are known for their golden coloration.
  6. Roach (Rutilus rutilus): Roach, a freshwater fish, have small, silvery cycloid scales that provide protection and reflect light.

2. Ctenoid Scale

Ctenoid scales of fish

Ctenoid scales, which are found on many bony fish species, are thought to have evolved from the cycloid scales of early bony fish.

Ctenoid scales are a type of fish scale characterized by tiny comb-like or toothed projections along their posterior (rear) edge.

These scales have small, tooth-like spines called ctenii on their edges, which give them a rough, spiky texture.

These projections, called ctenii, give ctenoid scales a rough texture compared to the smoother cycloid scales.

Ctenoid scales can overlap, and their rough texture provides additional protection to the fish against predators.

Ctenoid scales are used to reduce drag and improve the fish’s ability to swim, and are also used for protection and for signaling to other fish.

Several fish species have ctenoid scales, and they are often found in both freshwater and marine environments.

Here are some examples of fish with ctenoid scales:

  1. Perch Family (Family Percidae): Many species within the perch family, including the common perch, have ctenoid scales. These scales are typically colorful and are an identifying feature of this group.
  2. Sunfish Family (Family Centrarchidae): Sunfish species, such as bluegill and largemouth bass, have ctenoid scales. These scales can be quite large, especially in larger individuals.
  3. Surgeonfish (Family Acanthuridae): Surgeonfish, commonly found in coral reef environments, have ctenoid scales with a distinctive spiny projection at the base of their tail fin.
  4. Snapper Family (Family Lutjanidae): Many snapper species have ctenoid scales. These fish are important in both recreational and commercial fishing due to their flesh quality.
  5. Wrasse Family (Family Labridae): Wrasses, known for their vibrant colors, often have ctenoid scales. They are common inhabitants of coral reefs.
  6. Parrotfish (Family Scaridae): Parrotfish have ctenoid scales and are known for their beak-like mouths. They play a crucial role in reef ecology by helping to control algae growth.
  7. Porgies and Sea Breams (Family Sparidae): Many species in this family, such as the red porgy, have ctenoid scales.
  8. Basslets (Family Serranidae): Some species within the basslet family, like the royal gramma, have ctenoid scales.
  9. Angelfish (Family Pomacanthidae): Angelfish, often seen in marine aquariums, have ctenoid scales and striking color patterns.

3. Placoid Scales

This structure is made up of rhombic plates located in the corium, along with an odontoid outgrowth that extends to the back end of the fish’s body. It has three layers: vitrodentin, dentin, and pulp.

These scales are small, flat, and covered in enamel, making them very hard and sharp.

Placoid scales, also known as dermal denticles or “skin teeth,” are a type of scale found in cartilaginous fish, specifically in the subclass Elasmobranchii, which includes sharks, rays, and skates.

They are thought to have evolved from the dermal denticles (small, tooth-like structures) that covered the skin of early jawless fish.

Placoid scales are quite different from the scales found in bony fish (osteichthyes) like cycloid and ctenoid scales.

Here are the key characteristics of placoid scales and the fish that have them:

  1. Tooth-Like Structure: Placoid scales are small, hard, and flat structures that resemble tiny teeth. They have a central spine with backward-pointing ridges, which gives them a rough texture.
  2. Embedded in Skin: Unlike the scales of bony fish, placoid scales are not external structures but are embedded directly in the fish’s skin. They are anchored in a series within the dermal layer.
  3. Protective Function: Placoid scales serve as a form of armor, providing protection to the fish. Their tough structure helps reduce drag in water and prevents damage to the skin.
  4. Unique to Cartilaginous Fish: Placoid scales are exclusive to cartilaginous fish, which includes sharks, rays, and skates. These fish are characterized by their cartilaginous skeletons (as opposed to bony skeletons) and their unique scales.

Fish that have placoid scales include:

  • Sharks: Virtually all shark species have placoid scales. These scales are particularly well-developed in larger species like the great white shark and the tiger shark.
  • Rays: Many species of rays, including manta rays, stingrays, and electric rays, have placoid scales. These scales contribute to the tough and durable skin of rays.
  • Skates: Skates, which are closely related to rays, also possess placoid scales. They are found in various marine environments.

4. Ganoid Scales

Ganoid scales look like rhombic shapes with a tooth-shaped edge that interconnects with other scales to form armor. They have three layers: ganoine, cosmine, and isopedin.

Ganoid scales are a type of scale found in some ancient and primitive fish species, primarily in the subclass Chondrostei, which includes sturgeon and paddlefish, as well as in a few other fish groups.

Ganoid scales are found at the base of the upper lobe of the caudal fin in sturgeon fish, gar pike, and polypterus.

Ganoid scales are thought to have evolved from the cosmoid scales that covered the skin of early bony fish.

Ganoid scales are quite distinct from the scales found in most modern fish and are considered primitive in their structure and composition.

Here are the key characteristics of ganoid scales and some fish that have them:

  1. Hard and Bony Structure: Ganoid scales are composed of a hard, bony material called ganoin. This material makes these scales extremely tough and rigid compared to the softer scales of most modern fish.
  2. Overlapping Plates: Ganoid scales are typically large and thick, and they overlap like armor plating on the fish’s body. This overlapping arrangement provides excellent protection against predators and environmental abrasions.
  3. Diamond-Shaped or Rhomboid: Ganoid scales are often diamond-shaped or rhomboid in appearance, with a distinctive pattern of ridges and grooves on their surface. This pattern is used for species identification.
  4. Lung-Like Swimmer’s Bladder: Some fish with ganoid scales, like sturgeon, possess a unique lung-like structure called a “swimmer’s bladder” that allows them to gulp air from the surface. This adaptation helps them survive in oxygen-depleted waters.

Fish that have ganoid scales include:

  • Sturgeon: Sturgeons are perhaps the most well-known fish with ganoid scales. They are large, ancient fish that are highly valued for their roe, which is processed into caviar.
  • Paddlefish: Paddlefish, also known as spoonbill catfish, have ganoid scales. They are notable for their long, paddle-shaped rostrum and are found in freshwater rivers in North America.
  • Bowfin: The bowfin is a primitive fish found in North America. It possesses ganoid scales and is known for its aggressive nature.
  • Garfish: Garfish are elongated, predatory fish with ganoid scales. They are found in freshwater and brackish water environments.

Another Type Cosmoid Scales

Cosmoid scales are a type of scale found in certain ancient fish, such as coelacanths and lungfish.

These scales are made up of a layer of bone-like material, covered by a layer of cosmine, and a shiny outer layer of vitrodentine.

They are typically diamond-shaped and overlap each other, providing a protective armor for the fish.

Cosmoid scales are considered to be an intermediate stage in the evolution of modern bony fish scales.

Functions of Fish Scales | Why Do Fish Have Scales?

  • Protection: Scales provide a layer of protection for the fish’s body, helping to defend against predators and other external threats.
  • Streamlining: Scales help to streamline the fish’s body, reducing drag and allowing the fish to swim more efficiently.
  • Insulation: Scales help to insulate the fish’s body, helping to regulate its body temperature.
  • Communication: In some fish species, scales may be used for signaling to other fish, such as for courtship or aggression.
  • Sensory function: In some fish species, scales may contain sensory receptors that help the fish to detect changes in its environment, such as changes in temperature or pressure.

Uses of Fish Scales

Fish scales have a variety of uses, both practical and decorative:

  • Food: In some cultures, fish scales are considered a delicacy and are eaten as a snack or used as an ingredient in dishes.
  • Medicine: Fish scales have been used in traditional medicine for their alleged health benefits, including as an anti-inflammatory and for treating skin conditions.
  • Industrial uses: Fish scales are used in the production of various industrial products, including glue, paint, and cosmetics.
  • Art and crafts: Fish scales are sometimes used in art and craft projects, such as for making jewelry or decorations.
  • Fashion: Fish scales are sometimes used in fashion, such as for making bags or clothing.
  • Research: Fish scales are used in scientific research, such as for studying the evolution of fish and for tracking the movements of fish in the wild.

Scale Fish | Fishes Have Scales on their Body

Here are some types of scaled fish categorized into different groups:

  1. Bony Fish (Class Osteichthyes):
    • Bony fish are the most diverse group of fish, and they typically have scales covering their bodies.
    • Examples include salmon, trout, bass, and perch.
  2. Carp Family (Family Cyprinidae):
    • Many members of the carp family, including goldfish, koi, and common carp, have cycloid scales covering their bodies.
  3. Tuna and Mackerel (Family Scombridae):
    • These pelagic, fast-swimming fish have small, smooth, and overlapping scales that contribute to their streamlined shapes.
    • Examples include tuna (such as yellowfin and bluefin tuna) and mackerel.
  4. Salmonids (Family Salmonidae):
    • Salmonids, which include salmon and trout, have small, cycloid scales and are known for their anadromous life cycles.
  5. Perch-Like Fish (Order Perciformes):
    • Many fish in the order Perciformes, such as groupers, snappers, and angelfish, have ctenoid scales that are often colorful and vivid.
  6. Herring Family (Family Clupeidae):
    • Herring and related species have small, overlapping scales and are known for their importance in the fishing industry.
    • Examples include herring, sardines, and anchovies.
  7. Flatfish (Order Pleuronectiformes):
    • Flatfish, like flounders and sole, have small scales on one side of their flattened bodies.
  8. Tetras and Characins (Family Characidae):
    • Many tetras and characins have small scales and are popular in the aquarium trade.
    • Examples include the neon tetra and the silver dollar fish.
  9. Percidae Family (Family Percidae):
    • Members of the Percidae family, such as walleye and perch, have cycloid scales and are often freshwater species.
  10. Snook Family (Family Centropomidae):
    • Snook, prized by anglers, have ctenoid scales and are found in warm coastal waters.
  11. Parrotfish (Family Scaridae):
    • Parrotfish have scales that vary in size, and they are known for their distinctive beak-like mouths and roles in coral reef ecosystems.
  12. Piranhas (Family Serrasalmidae):
    • Piranhas are known for their sharp teeth but do have scales covering their bodies.
  13. Anguilliformes (Order Anguilliformes):
    • This order includes eels, which typically have small, cycloid scales or may be entirely scaleless. They are found in both freshwater and saltwater environments.
  14. Herrings and Anchovies (Family Clupeidae):
    • Herrings and anchovies have small, delicate scales that are important in the commercial fishing industry. They are often used for their flesh and oil.
  15. Haddock and Cod (Family Gadidae):
    • Fish in this family, including haddock and cod, have small, smooth, and overlapping scales. They are important in the seafood market.
  16. Salmon Sharks and Mackerel Sharks (Order Lamniformes):
    • These large, predatory sharks have dermal denticles, which are small, tooth-like scales that provide hydrodynamic advantages.
  17. Tilapia and Cichlids (Family Cichlidae):
    • Many cichlids, such as tilapia and angelfish, have ctenoid scales and are popular in the aquarium hobby.
  18. Flounder and Sole (Family Pleuronectidae):
    • Flatfish like flounder and sole have small scales on the eyed side of their flattened bodies, while the blind side lacks scales.
  19. Barracudas (Family Sphyraenidae):
    • Barracudas have small, sharp-edged scales and are known for their elongated, predatory bodies.
  20. Surgeonfish (Family Acanthuridae):
    • Surgeonfish, often seen in coral reef environments, have small, spiny scales and distinctive scalpel-like spines near their tails.
  21. Croakers (Family Sciaenidae):
    • Croakers have small, ctenoid scales and are known for the distinctive croaking sounds they produce.
  22. Sunfish (Family Centrarchidae):
    • Sunfish, including bluegill and largemouth bass, have ctenoid scales and are popular sportfish in North America.

Scaleless Fish | Fishes Don’t Have Scales on their Body

Scaleless fish belong to various taxonomic groups, and they can be found in both freshwater and saltwater environments.

Here are some common types of scaleless fish and their respective groups:

  1. Catfish (Order Siluriformes):
    • Catfish are among the most well-known scaleless fish. They have smooth skin without scales and often possess distinctive barbels around their mouths.
    • Examples include channel catfish, flathead catfish, and Corydoras catfish.
  2. Eels (Order Anguilliformes):
    • Eels are elongated, snake-like fish with smooth, scaleless skin. They are found in both freshwater and saltwater habitats.
    • Examples include the European eel and the moray eel.
  3. Loaches (Family Cobitidae and related families):
    • Loaches are small, bottom-dwelling fish known for their lack of scales and their unique behaviors. They often have barbels around their mouths.
    • Examples include the clown loach and the hillstream loach.
  4. Lampreys (Order Petromyzontiformes):
    • Lampreys are jawless, primitive fish with a sucker-like mouth. They have smooth, scaleless skin and are often parasitic, attaching themselves to other fish.
    • Examples include the sea lamprey and the brook lamprey.
  5. Pufferfish (Family Tetraodontidae):
    • While some pufferfish species have small, barely visible scales, many have a skin covered in tiny spines, giving them a scaleless appearance.
    • Examples include the freshwater figure-eight pufferfish and the saltwater porcupinefish.
  6. Sturgeon (Order Acipenseriformes):
    • Sturgeon are large, primitive fish with bony plates instead of traditional scales. These plates give them a unique appearance.
    • Examples include the beluga sturgeon and the lake sturgeon.
  7. Grunts (Family Haemulidae):
    • Some species of grunt fish have very small scales or scales that are difficult to see, making them appear nearly scaleless.
    • Examples include the French grunt and the blue-striped grunt.
  8. Sleeper Gobies (Family Eleotridae):
    • Sleeper gobies are small, bottom-dwelling fish often found in freshwater or brackish environments. They have smooth skin without scales.
    • Examples include the freshwater sleeper goby and the bumblebee goby.
  9. Knifefish (Family Apteronotidae):
    • Knifefish are freshwater fish known for their elongated, knife-like bodies and lack of scales. They use electrical fields for navigation and communication.
    • Examples include the black ghost knifefish and the glass knifefish.
  10. Gars (Family Lepisosteidae):
    • Gars are prehistoric-looking fish with long, slender bodies and hard bony plates rather than traditional scales.
    • Examples include the longnose gar and the spotted gar.
  11. Sticklebacks (Family Gasterosteidae):
    • Sticklebacks are small, spiny-finned fish with minimal or absent scales. They are known for their distinctive dorsal spines.
    • Examples include the three-spined stickleback and the nine-spined stickleback.
  12. Stonefish (Family Synanceiidae):
    • Stonefish are venomous, marine fish known for their remarkable camouflage and lack of traditional scales.
    • Examples include the reef stonefish and the devil scorpionfish.
  13. Blennies (Family Blenniidae):
    • Many blenny species have small or absent scales, and they are typically found in coastal marine and rocky reef environments.
    • Examples include the bicolor blenny and the lawnmower blenny.
  14. Sleeperheads (Family Parapercidae):
    • Sleeperheads are a family of marine fish known for their scaleless bodies and habitat in sandy or rocky areas.
    • Examples include the barred sandperch and the false morwong.
  15. Toadfish (Family Batrachoididae):
    • Toadfish are often scaleless and found in shallow coastal waters. They produce grunting sounds and have a distinctive appearance.
    • Examples include the oyster toadfish and the gulf toadfish.

Scale Fish Vs Scaleless Fish: Differences

CharacteristicScale FishScaleless Fish
Presence of ScalesPossess scales covering their bodies.Lack scales on their bodies.
Skin TextureSkin feels rough due to scalesOften have a smoother, slimy or mucus-coated skin.
AppearanceOften exhibit a shiny or metallic appearance due to scalesMay have a more matte or plain skin appearance
Common ExamplesMost common fish species, including trout, bass, and carp, have scalesExamples include catfish, eels, and some types of loaches
FunctionScales provide protection against predators and environmental abrasionsRely more on their skin’s mucous layer and other defense mechanisms.
MaintenanceRequire care to maintain scale health and prevent scale diseases.Generally have fewer scale-related health concerns.
Fish HabitatScale fish found in various aquatic environments, including both freshwater and saltwater.Scaleless fish can inhabit a wide range of aquatic environments, often in bottom-dwelling or specialized niches.
Texture of FilletFillets tend to have a firmer texture due to the scalesFillets are often softer and smoother in texture

Scale Development

The scales have rings called scleritis, which are visible under optical devices. The size of the rings increases with distance from the center of the scale and corresponds to the edge outlines of the scale.

The thickness of scales increases as new, larger scales grow beneath the old ones. The rings are located less and thicker, creating wider and narrower areas. The amount of scleritis zones formed each year corresponds to the age of the fish.

The scales consist of accrete flakes, with the smallest and oldest flakes at the top and the largest and youngest at the bottom.

The scales grow thicker every year due to the emergence of young scales with bigger size growing under the old scales. Fish grow unevenly throughout the year, which affects the growth of their scales.

Fish scales are thought to have evolved as a means of providing protection for the fish’s body.

Living beings have natural protection that has evolved over millions of years, which helps them survive in their surroundings.

Fishes, armadillos, and turtles have unique armor designs that provide outstanding mechanical properties such as high penetration resistance and toughness.

Over time, as different species of fish adapted to different environments and ecological niches, their scales also evolved to better serve their specific needs.

Frequently Asked Questions (FAQs)

Is fish scale good to eat?

In general, fish scales are not considered to be edible and are typically removed before cooking and eating fish.

While fish scales are not toxic or harmful to ingest, they are not typically consumed due to their tough, chewy texture and lack of flavor.

However, some cultures do have traditional dishes that include fish scales, and there are some health benefits associated with consuming fish scales, as they are a good source of collagen and may help improve skin health.

Do fish scales have protein?

Yes, fish scales do contain protein, as well as other nutrients such as calcium and phosphorus. However, the amount of protein in fish scales is relatively low compared to other parts of the fish such as the muscle tissue or fillet.

Additionally, the tough, fibrous nature of fish scales can make it difficult for the body to digest and absorb the protein.

Therefore, while fish scales do contain some protein, they are not typically considered to be a significant source of this nutrient.

Is there any relationship between fish length and scale size?

There is a relationship between the size of a fish and the size of its scales. As a fish grows longer, its scales also tend to increase in size.

This relationship can be used to estimate the size or age of a fish based on the size of its scales.

However, it’s important to note that this relationship can vary among different species of fish, so it may not always be an accurate predictor of size or age.

Are all fish scales the same size?

No, not all fish scales are the same size. The size and shape of fish scales can vary widely among different species of fish.

Some fish have small, circular scales, while others have larger, more complex scales with unique shapes and patterns.

Additionally, the size of a fish’s scales can change as it grows larger. Therefore, the size and shape of fish scales can be an important characteristic used to identify and classify different species of fish.

How old is a fish scale?

Fish scales can provide valuable information about a fish’s age. Each year, a fish typically adds a growth ring or band to its scales.

These rings, also known as annuli, can be counted to estimate the fish’s age. This method is commonly used in fisheries management and research to determine the age structure of fish populations.

Can a fish have more than one type of scale?

In most cases, fish have scales of a single type that is characteristic of their species. However, there are exceptions.

Some species of fish, particularly those in the family Cyprinidae (carp and minnows), can have two types of scales. These two types are called cycloid and ctenoid scales.

Cycloid scales are typically found on the body, while ctenoid scales are often present on the fins. Most fish, though, have scales that are consistent throughout their bodies.

Can scale type vary with sex?

Yes, in some fish species, the type or presence of scales can vary between sexes. This is more common in species where males and females have different physical characteristics, such as size, coloration, or body shape.

Some male fish may have specialized scales or other external features, such as tubercles or spines, during the breeding season to attract females or compete with other males for mating opportunities.

These variations in scale type or appearance can be sexually dimorphic and are often related to reproductive behaviors.