Age determination in coldwater schizothoracine fishes of the Kashmir Himalaya : Comparative evaluation of otoliths, fin rays and scales

Accurate age determination is fundamental to fisheries science, yet the precision of different calcified structures varies significantly across species and environments. This study provides the first comparative assessment of age estimation using whole otoliths, dorsal-fin rays and scales for endemic fish species in the Kashmir Himalaya. We collected 500 specimens of seven species (Schizothorax plagiostomus, Schizothorax niger, Schizothorax labiatus, Schizothorax curvifrons, Schizothorax esocinus, Crossocheilus diplocheilus and Triplophysa spp.) from various lakes and rivers. Age estimates from three independent readers were analysed using intraclass correlation coefficient (ICC), coefficient of variation (CV), paired t-tests and Bland-Altman plots. Whole otoliths consistently provided the most reliable age estimates across all species, with the highest precision and lowest inter-reader variability. Dorsal-fin rays offered a viable non-lethal alternative with moderate precision (e.g. ICC = 0.601-0.701 for S. niger and S. labiatus), whereas scales exhibited the highest variability and poorest reliability, particularly in older fish (CV up to 145% in S. esocinus). Species-specific performance varied, with S. plagiostomus showing the most consistent results across all structures, and S. curvifrons and S. esocinus exhibiting high intra-reader variability. These findings underscore the necessity for structure-specific and species-specific calibration in ageing studies. We recommend otoliths for high-precision demographic studies and fin rays for non-lethal monitoring, providing a critical foundation for developing standardized ageing protocols and sustainable fisheries management in the region.