Daily incuremtns in Otoliths of juvenile Snapper, Pagrus auratus (Sparidae)

Abstract

Sagitta microstructure was investigated in juvenile New Zealand snapper, Pagrus auratus, to provide a basis for daily ageing in population dynamics studies. Transverse sections produced the clearest daily increments and were the easiest to prepare. Daily increment formation was validated up to an age of 100 days by using increment counts from reared juveniles and up to about 160 days by using changes in mean increment counts from juveniles sampled from a wild population at different times. A prominent metamorphic mark was visible in transverse and frontal sections, providing a means for determining the duration of the larval period, and juvenile postmetamorphic ages. Postmetamorphic increment width varied with the age of the snapper and with season. Increment width dropped below 0.5 μm in winter and increments could not be resolved with a light microscope.