There are four main types of fish scales each with their own characteristics.

Each type of scale has its own functions and appearance and has specific fish type that they belong to.

Ganoid Scales

Ganoid scales are a rhombus shaped scale which are found of bony fish like the sturgeon. These scales can be called scutes and are designed in a way to protect as opposed to allowing extra movement for the fish.

The molecular make-up of the scute is that they are a modified cosmoid scale, (type of scales most associated with fossilised fish) they consist of a bony innermost layer. This layer regenerates often and allows for the fishes’ scales to continue to grow as the fish grows and reaches maturity. As with the placoid scales the inner layer of these scales is made up of dentine, (the main part of the tissue found in teeth beneath the enamel). The outer most layer is a shiny layer which does resemble enamel and is made up of inorganic bone tissue called ganoine. This helps to allow the scales to be compressed with a great deal of force before they do in fact get damaged and this function helps to protect the fish from predators.

The design of the scale is to function as a preventative structure against being punctured and to dispense the amount of pressure caused by compression to lessen the amount of damage caused to the fish. Alongside of this protection the fish have been known to have a thin coat of mucus that covers the scales, this protects them from scrapes and other types of injuries caused by rubbing, such as grazes.

These scales tend to be described as armour like due to how protective they are for the fish. In addition to the protection that these scales provide they also help the fish to be more protected from temperature changes and aids them in self-regulating their own temperature.

Fish that have ganoid scales have been known to survive in oxygen deprived areas like bogs where oxygen levels are in fact lower than in most areas where most of the other fish breeds would ordinarily not survive in oxygen deprived areas.

Ctenoid and cycloid Scales

As these scales as remarkably similar in both their functions and appearance with a few minor exceptions and they both occur on the same classification of fish (Osteichthyes). The following information applies to both types of scales.

The scales are large thin and round they are flexible and continually overlap from head to tail. As with the other types of scales this creates a streamlined effect and allows the fish to move through the water without too much resistance. These scales continue to grow with the fish, and this is where they create a ring pattern on each scale. This can be used to guess the age of the fish with a degree of accuracy.

The outer layer of these scales is made of calcium and has an inner layer of connective tissues. The fish have a level of protection with both these scales as they protect the skin of the fish underneath the scales, and they are also protected from environmental factors too such as abrasions from surfaces and other fish in the vicinity.

In addition to the protective qualities the scales also help with thermoregulation by allowing the water that is stuck between the scales and skin to function as a temperature to help maintain and regulate the temperature of the fish.

Whilst the main function and the molecular build-up of these scales is identical there is one difference between the two, the scales are large oval shaped and have a free edge which overlaps. On the cycloid scales this free is edge is smooth and rounded.

However, on the ctenoid the free edge lives up to its name which is taken from the Greek word “cteno” this means comb. The free edge of the ctenoid is round but not smooth it is shaped like a comb with teeth that protrude the free edge. this difference although it is small helps to identify the breed of the fish and species.

Placoid Scales

The appearance of these scales varies, dependent on what breed of fish they belong to. These scales have the same build up as teeth. They are supplied with blood on the inside at the core of the scale, this is protected by a layer of dentine the main proportion of tissue that makes up the structure of the tooth with enamel as the outer most part. These are called denticles, these scales are shaped like curved teeth and are extremely tough. They function as a protective layer, but they also have a rough exterior texture similar to sandpaper which can be used as an additional way to injure the desired prey or potential predators.

The scales main design each scale is embedded into the skin of the shark with an oblong base and is a V shape which allows the amount of drag against the fish whilst swimming to be decreased and enables to the fish to glide through the water faster and quieter despite the size of the host. The scales are all streamlined leaning back and pointing from the head to the tail, this allows the fish to swim faster and move more efficiently through the water., in turn it allows the fish to use less energy as they hunt swim and survive. As mentioned previously, these scales whilst they have the same molecular build up and structure, some of these scales can be structured slightly different on the surface. This can be that the scales have spines or ridges which stick out slightly towards the rear of the fish and help to provide a more protective surface.

Unlike the other types of scales these placoid scales do not continue to grow with the fish, instead as the fish grows the scales separate and when a gap appears the fish grows a new scale in its place to create a protective layer for the exposed skin and this pattern continues until the fish is fully grown.