POWER AND SYRED / SCIENCE PHOTO LIBRARY POWER AND SYRED / SCIENCE PHOTO LIBRARY
Rainbow trout scale. Coloured scanning electron micrograph (SEM) of a rainbow trout (Oncorhynchus mykiss) scale. Fish scales are are classified by shape. Trout scales are known as cycloid (curve edged). As the fish grows, the scale increase in size and growth rings called circuli become visible. During cooler months of the year the scale grows more slowly and the circuli are closer together leaving a band called an annulus. By counting the annuli it is possible to estimate the age of the fish. Magnification: x36 when printed 10 centimetres wide.
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