Recent studies have reported growth marks in the gastric ossicles and eyestalks of decapod crustaceans (Leland et al., 2011¹ ; Kilada et al., 2012² ).  The relative utility of ageing structures and validation methods (i.e. calcein staining and LA-ICPMS) for subtropical marine and freshwater species was assessed using giant mud crab (Scylla serrata) and redclaw crayfish (Cherax quadricarinatus) models.  Internal and external hard parts from C. quadricarinatus contained both primary and secondary growth marks that could be used for age estimation.  Scylla serrata counts were based on the primary series in zygocardiac ossicles.  The maximum estimated age for S. serrata and C. quadricarinatus (4 and 3 years) are consistent with previous longevity information, but correlated weakly with size.  Preliminary validation results demonstrate long-term (215 d) calcein retention through consecutive moults (for S. serrata) and the potential usefulness of temperature-sensitive elemental ratio mapping (e.g. of Boron, Barium and Magnesium) for crustacean age validation.  On the weight of evidence, it appears that primary growth marks are probably deposited annually, but further research with a longer post-staining grow-out is needed to provide a definitive validation.  Further assessment of alternative calcein concentrations, exposure durations and/or chemical markers could improve the existing techniques and facilitate their application to other commercially important long-lived decapods.