Ageing Belanger's croaker, Johnius belangerii (Cuvier, 1830), based on otolith shape analysis

The use of morphological characters and otolith weight as predictors of fish age has proven to be an efficient, objective and precise method, but studies were heretofore focused primarily on fast-growing fish species. In the present study, Belanger's croaker, Johnius belangerii (Cuvier, 1830), is presented as a model species for slow-growing fish where it is hypothesized that age has a significant effect on the otolith shape, and that the otolith weight has the potential to predict individual fish age as an alternative and objective method. Discriminant function analysis (DFA) of shape variables and cross-validation were applied to a total of 359 sagittal otoliths in the age groups 0, 1 and 2. The shape variables demonstrated 64.1% correct age classification, and a 93.5% correct age classification with the inclusion of otolith weight in the discriminant function. Results show that a combination of shape variables and otolith weight work well in age determination of Belanger's croaker, and demonstrate its application potential for sciaenids that are distributed throughout the coastal waters of China.