Reptile scales are made in the epidermis, and are more like fur or feathers. The scales have a core of vascular bone, which means they have blood flow. This is covered by a layer of dentine or enamel, much like teeth. Some scales also have an outer layer of keratin.
This is the protein that makes up nails and hair. Placoid scales, the kind sharks and rays have, are covered in enamel and resemble teeth under a microscope.
Cosmoid scales are also covered in enamel, over a surface of dentine and the inner core of bone. The ganoid scales of gar, have an enamel shell like placoid scales. They also have a peg and socket joint in between them.
Ctenoid scales, possessed by trout, and other bony fish do not have a hard enamel coating. They are covered in keratin, which makes them more flexible. If you look closely at scales, you will see that they overlap forming a dense surface. Some scales even have serrated edges. Scales act almost like armor protecting the fish from predators, and scrapes on rocks and branches.
All fish have a slime coat secreted from under the scales. This slime coat keeps the fish moist. It also protects against infection and parasites. Some fish have a toxic slime layer, another defense against predators. Most fish do not shed their scales, unlike reptiles who shed their skin as they grow.
This outermost layer of protection contains tiny glands that produce that slippery mucus we feel when we touch a fish. That mucus is more important than simply helping the fish slip out of a predator's grasp: It shields the fish against bacteria , pollutants and harmful substances in its environment.
Scales also allow fish to be more streamlined and flexible in the water. The way they overlap enables the fish to bend and curl despite being covered in these solid plates. It is not always the case, but faster swimming sharks usually have overlapping denticles. Slower swimming sharks often have courser non-overlapping scales.
Scale sizes vary greatly between species. Some fishes, such as the freshwater eels have tiny embedded scales. Fishes such as the tunas have tiny scales often found in discrete areas of the body. Many fishes such as the Coral Snappers have medium sized scales whereas the scales of others such as the Tarpon, Megalops cyprinoides , are large enough to be used in jewellery.
The scales of the Indian Mahseer, Tor tor , are known to reach over 10 cm in length. As cycloid and ctenoid scales increase in size, growth rings called circuli become visible.
These rings look a little like the growth rings in the trunk of a tree. During the cooler months of the year the scale and otoliths grows more slowly and the circuli are closer together leaving a band called an annulus.
By counting the annuli it is possible estimate the age of the fish. This technique is extensively used by fisheries biologists. These are the scales - the skin - of a blue Siamese fighting fish, and they almost look like a piece of art.
They also look like they form a smooth, streamlined skin. Why is this important to a fish? Fish are aquatic vertebrates. They make up more than half of all vertebrate species. They are especially important in the study of vertebrate evolution because several important vertebrate traits evolved in fish.
Fish show great diversity in body size. They range in length from about 8 millimeters 0. Most are ectothermic and covered with scales. Scales protect fish from predators and parasites and reduce friction with the water. Multiple, overlapping scales provide a flexible covering that allows fish to move easily while swimming. Many structures in fish are adaptations for their aquatic lifestyle.
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