Mass‐effect: Understanding the relationship between age and otolith weight in fishes

The estimation of age on a fish by using the otolith weight is a quick and low‐cost technique, yet controversial despite separate researchers worldwide have proved successfully its application. A systematic review was conducted including 47 publications containing 289 data points where the relationship between the age and otolith weight was assessed. Here, a meta‐analysis of the age and otolith weight relationship at a global level is provided. A random effect model was used to estimate the effect size (Pearson's correlation coefficient) of each study as well as the overall effect size. A strong effect in age–otolith weight relationship was detected with an overall effect size of r  = 0.93 (95% CI: 0.91 to 0.94) and a high observed heterogeneity ( Q T  = 8,107.63, df  = 288, p  < .001; I 2  = 96.62%). Four significant moderator variables were identified (families, habitats, models and regions) where heterogeneity was large (≥90%) while the families were the best moderator according to AIC criteria ( Q M  = 378.12, df  = 28, p  < .0001; I 2  = 89.97%). Overall results suggest that otolith weight has a positive effect correlation over the age estimation of fish.