Reproducibility of age determination by scale and vertebra in pontic shad (Alosa pontica Eichwald, 1838), from the Danube

Specimens of Pontic shad (Alosa pontica Eichwald, 1838) were collected during April and May of 2006 in the Danube River (rkm 863) just downstream of the Iron Gate (Djerdap) II dam. Twenty-eight scales and 30 vertebrae were prepared and given to five interpreters with fish aging experience of from 3 to 30 years and with shad aging experience of from 0 to 12 years. Interpreters with experience in shad age determination showed lower values for the index of average percent error (IAPE) and an index of coefficient of variation (ICV). In regard to within-interpreter reproducibility, no significant differences were found between scale and vertebrae as structure for age determination. The most experienced reader showed the lowest value for IAPE, while the least experienced reader showed the highest value for IAPE. The results of this work indicate that experience in age determination by particular structure had more impact on age determination precision than specificity of structure, scale or vertebra. More work is needed on adopting standard protocols that must include some sort of common interaction between responsible age readers