Ageing Nile tilapia (Oreochromis niloticus): A comparative study between scales and otoliths

This study is the first to compare age estimates based on scales and otoliths of the Nile tilapia, Oreochromis niloticus, from Lake Nasser, Egypt. Ageing precision between readers was estimated by calculating the percent agreement between three independent readers, and the coefficient of variation (CV) ages estimated from otoliths and scales. The relation between the total length of fish and the radius of its scale and otolith was determined and appeared to be linear. The estimated age composition of the O. niloticus included six age groups estimated using scales and five age groups estimated by otoliths. The relative precision (CV and SD) of ages estimated from otolith was higher than that from scales. Higher percentages of agreement of overall annuli identification and age assignment between readers were noted in otoliths comparing to that in scales. Scale showed some inaccurate estimation in the age of fish older than 4. The precision and bias information in this study will be beneficial to fisheries professionals in assessing the age of Nile tilapia and other cichlids in the future.