Mulloway Stock Enhancement Project

To see if the mulloway we captured is one those released during this project, we need to extract the otolith or earstone from the fish. The otolith sits at the back of the brain in most fish, and its function is to give the fish balance and orientation in the water, much like the middle ear functions to give humans balance.

The otolith is found in the head of the mulloway, in the region marked by the arrow.

Once the otolith is extracted, it is embedded in resin, and is ready for sectioning. A thin layer of material is deposited around the otolith every day. These form rings inside the otolith, and by counting the rings we can tell how old the fish is, much like we can by counting the growth rings in a tree. To reveal the growth rings in the otolith, we take a thin slice or section of it using a special saw.

Otoliths embedded in resin. The small white oval shaped objects shown by the arrows are the otoliths.

This is the special saw we use to section mulloway otoliths. A motor turns the blades while a small pump sprays water on the otolith for lubrication.

The cutting system consists of two blades separated by a small spacer. These blades turn at high speed and produce a thin wafer of resin and otolith. The wafer is thin enough for light to pass through when viewing down the microscope.