The scales of a fish are slanted in the skin of the fish and consist of collagen, calcium phosphate and calcium carbonate. They overlap and form a firm layer that protects the fish against injuries, parasites and enemies. In many cases they also serve as reflectors or give colors.
Ctenoid scales are classified under the elasmoid scales. Most fish have elasmoid scales, which can be used for the age determination of the fish. This is done by counting the concentric lines on the scale that are formed as the fish grows. Ctenoid scales are like cycloid scales that are also classified under the elasmoid scales. Cycloid scales however, do not have the typical small teeth on the outer edges.
The concentric lines can be clearly seen in the photographs. The scales also exhibit auto fluorescence, for example on excitation with green light, and under the polarization microscope the chemical components present in the scale provide for beautiful color effects. The fluorescent properties of the skin (scales) of fish have an important function, such as communication.
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