However, the canals of the inner ear, where otoliths reside, are quite similar to that of humans. An otolith is dissected out of the fish's brain, embedded in a block of resin and ground down on both sides to a very thin cross section. Each sample must be thin enough for light to penetrate while observed with a compound microscope. The image of the otolith is then sent through a video camera and projected to 300 times its size onto a video monitor. The result is a physical count of all increments from the central region out to the edge of the otolith and an analysis of the rate of growth spanning the radial distance of the otolith.
Increment width is an indirect measurement of growth.
Warmer water or nutrient-rich food sources increase fish growth. This increased growth can be reflected on an otolith. Therefore, it is likely that a habitat transition from fresh to salt water would be reflected on an otolith. This is most notable in species such as pink salmon, which migrate abruptly from fresh water to salt water. This abrupt change in habitat is seen as a transitional point on the otolith.