Use of hatchery-raised fish in validation of daily age estimates for juvenile Common Snook

Abstract Objective We investigated the validity of daily age estimates for juvenile Common Snook Centropomus undecimalis by using sectioned and sanded sagittal otoliths. Methods Common Snook have a protracted spawning season, which is problematic for validation of daily ages because a hatch date—needed to calculate age—cannot be reasonably assigned like it can for species with a short spawning period (<30 days). To help overcome this, two readers independently counted presumed daily increments in otoliths collected from hatchery-reared Common Snook of known age (100–240 days; n = 91). Result Differences between known ages and those estimated from otoliths were small (mean absolute difference = 3.4 days) for individuals aged 100 days, but these differences increased after 100 days, mainly due to the crowding of increments along the otolith margin. Underestimation of ages was 8% at 120 days, 29% at 180 days, and 36% at 240 days. Conclusion Ideally, analyses based on counts of daily increments in Common Snook otoliths should be limited to fish with an age of 100 days or younger.