Fish traceability: Guessing the origin of fish from a seafood market using fish scale shape

Fish traceability is an important tool in fish food safety and a recognition tool in the assessment of biodiversity and fisheries. Geometric morphometric methods were used to establish whether scale morphology may determine the origin of specimens from a fish market. In order to trace the origin of fish, the fish scale shape of two mugilids species Mugil cephalus and Mugil curema specimens from three different trade premises at the Mexico City central fish market was analyzed and compared with the scale shape of previously collected samples from known areas along the Gulf of Mexico and Pacific coasts. The origin of the fish market specimens was kept in a closed envelope and was revealed at the end of the study. Scale shape was described using seven landmarks, the coordinates of which were subjected to a generalised Procrustes analysis, followed by a principal components analysis and discriminant analysis. Discriminant classification was used as the main indicator to identify the source of the fish, where the percentage of discrimination traced the origin of the specimens, respectively. A leave-one-out procedure was applied to validate the results of discriminant functions on shape, and relative warp in size-shape space (shape plus size). Results showed that the discriminant analysis correctly classified 83.3% of the cases, with 100% for adjacent geographic areas. The relative warp in size-shape space (shape plus size) of fish scales could be used to reliably trace fish populations by applying geometric morphometric methods to one fish scale per specimen. In order to effectively use such an approach in fisheries management, it is necessary to have previous patterns of fish scale shapes for each locality. Since the scale shape was described using seven landmarks, it may be possible to improve the tracing rate by increasing the number of landmarks used. Fish scale shape thus offers a straightforward, accessible, quick and inexpensive method to trace fish stocks.