Ok my mate Tyson whipped the ear bones (called otoliths) out of the Moses and hussar today. Otoliths are like our ear bones - they help fish stay upright in the water and hear sounds. You might have heard or seen the “jewels” from mulloway - these are their otoliths. They come in all shapes, sizes and thicknesses depending upon the type of fish’s habitat and behaviours.
They sit in a cavity under the brain (slightly behind and above the top of the eye) so depending on the species of fish you can access them from the top (by scalping the fish) or from underneath. For the hussar and Moses Tyson cut away the gills and went from underneath.
We use bone cutters to prise open the cavity, and the otoliths can be plucked with some fine tweezers.
Some species’ otoliths (ie mackerel, tailor, bream) can be viewed whole under a microscope, but fish like snapper, pearl perch, mulloway, red emperor, Moses and hussar need to be set in a block of polyester resin and a thin slice cut using a low speed saw. The slice is then mounted on a slide and viewed under a microscope.
The otolith displays growth rings (like in the trunk of a tree) and show periods of fast growth (wide, clear material) and slow growth (narrow, opaque rings) that corresponds with annual cycles. There’s a bit of science to determine whether a fish species lays down annual rings, but generally this applies for most fish.
So now we have the otoliths of these two fish out, we have a bit more work putting them in blocks and slicing them before we can estimate their age.
I’ll post the next steps as I get round to them.