If you want to easily identify your catch during your next fishing trip, you want to learn about different types of scales in fish. Fish scales are a thin, firm plate that grows on top of the fish skin. Scales on fish have the primary goal of providing them with camouflage.
They do so through their colorations and reflection. This mechanism proves to be effective against evading predators. In addition to camouflage, fish scales offer hydrodynamic benefits. They allow fish to easily survive and move through their habitat.
However, for anglers, fish scales also help in identifying the different types of fish. In the guide below, we’ve shared an in-depth breakdown of the different types of fish scales. The guide can help you identify the different fish species the next time you are out on the water.
Uses of Fish Scales
As mentioned above, fish scales come in handy when identifying fish. But, as part of the most outer layers of a fish, scales do more than just assisting in identification. Other key features of fish scales include:
- Acting as camouflage against predators by using their reflection and coloration to match the surroundings.
- Improving mobility in water and reducing drag.
- Protecting fish against microbial infestation – the scale surface makes it difficult for organisms to attach to fish.
- Preventing dehydration as they maintain water balance inside the fish.
What Are the Different Types of Scales In Fish?
As you continue to come across diverse species of fish, you will notice their differences in scales. Fish scales vary in shape, structure, size, and even texture. Typically, there are four main types of fish scales. These include placoids, cosmoids, ganoids, and cycloid/ctenoid.
However, these four types of scales also have their variations, divided into subtypes. Additionally, some fish scales types are considered to be ancient – some of which have already gone extinct. In this guide, we will focus on the four main modern and existent fish scales.
Cosmoid Fish Scales
Typically found in lungfish and some fossil fish, cosmoids originate from a fusion of fossil fish. Most fish with cosmoid scales, however, have gone extinct. Cosmoids scales feature a dense isopedine inner layer.
Between the inner layer and outer layer is a vascular bone maintained by blood vessels. Atop the vascular layer is complex dentine-like cosmine top layers. This top layer also features a superficial outer coating.
Ganoid Fish Scales
Ganoid fish scales originate from cosmoid scales. But, their difference is that ganoid fish scales feature serrated edges. Unlike cosmoid scales, these scales only have two layers. These include a layer of hard enamel and a layer of inorganic bone salt.
The inorganic layer is also known as ganoine. In fact, due to its uniqueness, anglers use the ganoine layer to identify ganoid fish scales. A ganoine layer normally has a glassy surface with sub-layers of mineral tissues. Additionally, ganoine layers mimic the strength of tooth enamel.
In some fish species such as bichirs and gars, you will notice that the scales come with cranial bones, too—fish such as sturgeon, paddlefish, bowfin, gar, and bichir feature ganoid scales. On the surface of a fish, ganoid scales appear to be diamond-shaped and connected like joints. Whilst they feature a glassy layer, they are actually thick (nearly impenetrable).
The diamond patterns fit tightly between each other, almost overlapping. But, in some fish, the patterns may differ. For example, on sturgeons, the scales feature a larger design on the sides and front to mimic armor plates. However, at the back of the fish, the scales are slightly thinner.
Cycloid/Ctenoid Fish Scales
Found in bony fish, cycloid and ctenoids scales fall under a larger group known as the leptoids. The leptoid fish scale group refers to fish with bony ridged scales. Leptoids tend to be thinner, less dense, and translucent compared to other fish scales.
Furthermore, the scales tend to be softer and increase in layers as the size of the fish increases. Outer parts of leptoid scales tend to have fanned out bony ridges. Their inner parts have a more fibrous connective tissue design in a criss-cross pattern.
Thus, in physical form, the scales mimic roofing tiles arranged on the roof of a house. Due to this pattern, leptoid scales play a significant role in aerodynamics. The pattern and structure promote smooth gliding through the water while reducing drag.
Cycloid Fish Scales
Cycloid scales get their name from their circular patterns. These types of scales tend to be smooth and even with an outer margin. You will find cycloid scales in fish such as salmon, trout, and carp.
Ctenoid Fish Scales
Ctenoid fish scales are quite like cycloids. But, the two fish scale types also bear differences. The most distinctive difference is that ctenoid scales are almost toothed. These scales have small teeth known as ctenii on their outer edges. Due to the teeth, their edges tend to be rougher. You will find these types of scales on fish such as perch, sunfish, drum fish, and ray-finned fish.
Placoid Fish Scales
Larger fish such as sharks and rays feature placoid scales. These scales feature a pointed and tooth-shaped finish. Also known as dermal denticles, these scales have an even structure with small teeth.
In the interior, the scales have a central pulp cavity with vessels and a conical layer covering them. Their outer layer, on the other hand, looks like that of cosmoid scales. Unlike other scales, placoid fish scales don’t enlarge as the fish size increases. Instead, they increase in numbers.
Other Fish Scales
Other types of fish scales include thelodonts and elasmoids. Thelodont fish scales are amongst the most abundant fossil fish scales. These fish scales originate from species related to modern fish such as elephant sharks, chimeras, and rabbitfish.
Thelodonts are designed with a keratin top layer. Similar to cosmoids, thelodont scale size increases as the fish size increases. Elasmoid fish scales, on the other hand, are typically found in some extinct lungfish and zebrafish.
In some cases, you will come across fish with scutes. While some people may consider them scales, scutes aren’t classified as scales. They resemble scales and serve the same purpose. Scutes are formed from the epidermis of the fish in the lower vascular layer.
Like scales, they also feature a bony and thick like exterior. Typically, fish such as river herring and pinecone fish have scutes instead of scales.
Modern Fish Scales
In addition to the four main modern fish scales, you can find unconventional scale designs. A good example of these designs includes scales on pufferfish and porcupine. Unlike regular fish, these fish species feature spines instead of scales.
But, their biology is slightly different. Due to their breeding, pufferfish have developed thin and inconspicuous spines. These spines only become visible when they puff up as a defense mechanism against predators.
Porcupinefish, on the other hand, have more visible spines modified from scales. Other fish species with distinctive scales include anchovies and herrings. These types of fish easily shed off their scales to escape predators and grow new ones.
What Are Fish Scales Made From?
Like teeth and bones, Fish scales are made from enamel and hard, dense, bony tissues. Some scales even feature protein materials such as keratin and collagen.
Do All Fish Have Scales?
You can find fish with and without scales. Fish without scales include species such as jawless fish, eels, catfish, mandarin fish, and anglerfish. Scales protrude from the skin layer underneath the fish and don’t only exist on the surface.
Do All Fish Have One Type of Scale?
Not all fish have a single type of scale pattern; you can find some fish with two or more scale designs. For example, some flounders feature ctenoid scales on the side of the body. However, in other areas of their bodies, they are marked with cycloid scales. In other cases, scale designs differ based on gender. For example, in some species, you will find male fish with ctenoid scales and female fish with cycloid scales.
Can I Eat Fish Without Scales?
Some people do have scaleless fish such as catfish as part of their delicacy. But, other people, such as some Christians, don’t consume scaleless fish due to their religious beliefs. But, scaleless fish also pose a higher risk of toxicity and carrying microbial organisms.
As proven by the guide above, learning about different types of scales allows you to know more about fish. As scales exist under different groups with certain characteristics, they make it easier to know more about the fish.
For example, faster fish have overlapping scales to complement their reduced drag and high-speed performance. Slower and smaller fish, on the other hand, less overlapping scales. But, this is not all scales do. After all, scales don’t only bring benefits to the fish.
They also widely benefit humans. Their most significant advantage is that they play a role in preserving the freshness of your catch after nabbing them from the water.