Validating Otolith Annuli for Annual Age Determination of Common Carp

Abstract

Common carp Cyprinus carpio are an important pest species in Australia, yet little is known regarding their age and growth there. We examined otolith sections of common carp to validate their utility for age determination. For the 1999 year-class in Hut Lake near Barmah, we confirmed the absolute age at first annulus formation as age 1 by repeated sampling of a discrete young-of-year cohort. We confirmed the annual periodicity of annulus formation for common carp in a mark–recapture experiment when 19 recaptured adult common carp (from an original stocking of 141 fish marked by injection with oxytetracycline (OTC)) showed visible fluorescent marks on their otoliths. Time at liberty for these fish ranged from 6 to 25 months, and their ages on recapture ranged from 3 to 14 years. Increment counts outside the OTC mark agreed completely with time at liberty. We calculated precision estimates on age determinations as the average percent error (APE) and estimated the coefficient of variation (CV = −0.15 + 1.41APE) between readers and for each of two readers over time. Precision was assessed by rereading subsamples. The APE was less than 5% and CV was less than 8% in all cases. We conclude that examination of thin otolith sections is a suitable method for the determination of annual age estimates for common carp age 0–14.