Fish scale shape variation by year and by geographic location, could scales be useful to trace fish? A case study on the Gulf of Mexico

•Time variations of scale shape have never been addressed in the literature.•No significant differences in scale shape were detected by year.•Still fish scale shapes differentiate among geographic variants.•Average scale shape by geographic variant followed a similar behavior through time.•This is a practical paper with potential for fish traceability.

Fish scale shape has been used to discriminate between stocks notwithstanding that variations in shape generated by different timings of sample collection have never been addressed in the literature. Considering that time could affect different locations in a similar way, scale shape differences may be useful to trace fish. The purpose of this study was to determine if fish scale shape vary by year and by geographic location for Mugil curema, through a wide and complete sampling. Geometric morphometric techniques were applied to the fish scale shapes with a MANOVA to compare the shape among groups (years and geographic locations). Also discriminant analysis was used to determinate the efficacy of scale shape in discriminating by location. No significant differences in scale shape were detected by year, whereas it was possible to distinguish shape differences among geographic locations. These results indicate that scale shape differences may be useful to trace fish when having a previously recorded pattern for each locality.