Age and growth of a large tropical anchovy, Thryssa hamiltoni (Gray): A comparison of ageing techniques

Abstract

Three principal ageing methods were used to describe the growth history of Thryssa hamiltoni, a large tropical anchovy from the waters off Townsville, north-eastern Queensland. The study was undertaken to compare ageing methods based on length-frequency analysis that are commonly applied in age and growth studies of tropical clupeoids, with less commonly used methods based on daily and seasonal growth rings in otoliths. A preliminary study suggested that seasonal growth rings in the sagittae of T. hamiltoni were formed annually and were therefore useful for age estimations for this species. Age and growth estimates derived from the three methods were consistent, with the results of each method supporting the results of the others. Direct validation of daily growth increments in T. hamiltoni by means of tetracycline marking experiments was unsuccessful due to the sensitivity of this species to handling stress. The distribution of modes in length-frequency histograms, and age estimates based on annual growth rings, both showed that male and female T. hamiltoni exhibit different growth patterns, with females growing faster and attaining greater maximum lengths than do males. Although counts of annual growth rings suggest a maximum longevity of 4 years for both males and females, lengthfrequency data indicate that the population is largely comprised of fish up to 2 years of age.