Validation of age determination from otoliths of the King George whiting Sillaginodes punctata (Perciformes)

Abstract

The otoliths of the King George whiting Sillaginodes punctata were assessed for their usefulness in adult-ageing. Whole, transverse-sectioned and broken/burnt sagittae displayed alternating opaque and translucent zones. Some small whole otoliths contained accessory areas of pigment, whilst large otoliths were too thick to transmit light, resulting in ambiguous counts in each case. Both marginal-increment analysis and treatment of fish with tetracycline demonstrated that the first three opaque zones formed annually, the first during the spring/summer of the second year of life, and the second and third in each subsequent spring. Otolith thickness increased linearly with the completion of each new opaque/translucent zone. An ageing protocol based on whole otoliths, supplemented with the breaking/burning of ambiguous otoliths is recommended. An algorithm for calculating age in months from otolith counts based on a fixed birth-date of the mid-point of the spawning season is presented.