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.

Fish scales have a range of industrial uses, for creating lightweight, durable materials from cosmetics to traditional medicines.

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, including salmon, trout, and bass. Cycloid scales are small, round scales that overlap like shingles on a roof.

They are flexible and smooth, and are used to reduce drag and improve the fish’s ability to swim.

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.

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

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.

3. Placoid scales

Placoid scales, which are found on cartilaginous fish such as sharks and rays, are thought to have evolved from the dermal denticles (small, tooth-like structures) that covered the skin of early jawless fish.

These scales are small, flat, and covered in enamel, making them very hard and sharp. They are used for protection and for streamlining the body to reduce drag.

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.

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 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.

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

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.

Fishes Have Scales on their Body

There are many groups of fish that have scales on their body. Some examples include:

Bony fish: Most bony fish, which make up the majority of fish species, have scales on their body. These scales may be cycloid, ctenoid, or ganoid in structure, depending on the species.

Salmon: Salmon are a group of bony fish that have cycloid scales on their body.

Trout: Trout are a group of bony fish that have cycloid or ctenoid scales on their body, depending on the species.

Bass: Bass are a group of bony fish that have cycloid or ctenoid scales on their body, depending on the species.

Perch: Perch are a group of bony fish that have ctenoid scales on their body.

Gar: Gar are a group of primitive bony fish that have ganoid scales on their body.

Bichir: Bichir are a group of primitive bony fish that have ganoid scales on their body.

Scaleless Fish

There are several groups of fish that do not have scales:

Cartilaginous fish: This group of fish, which includes sharks, rays, and skates, has a skeleton made of cartilage instead of bone.

These fish do not have scales, but they do have placoid scales, which are small, hard scales that are covered in enamel and are arranged in rows along the body.

Lampreys: Lampreys are a type of jawless fish that do not have scales or bones. They have a primitive, eel-like body and a sucker-like mouth that they use to attach to other fish to feed on their blood.

Hagfish: Hagfish are another group of jawless fish that do not have scales or bones. They have a slimy, eel-like body and are found in the deep sea.

Lungfish: Lungfish are a group of air-breathing fish that have the ability to survive in low-oxygen environments by using their lungs to breathe air. They do not have scales, but they do have bony plates on their body for protection.

Eels: Eels are a group of elongated, snake-like fish that do not have scales, but they do have a slippery, slimy skin that helps to reduce drag as they swim.

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.


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.


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