Using molecular phylogenetic and stable isotopic analysis to identify species, geographical origin and production method of mullet roes

Abstract

The flathead grey mullet, Mugil cephalus (Mugilidae), is one of the most commercially important fish species in Taiwan since mullet roe is considered as a delicacy with a high economic value. Farmed, wild-caught, and imported mullet roes are often not properly labelled in retail stores and merchants can make unethical profits from selling mislabeled products. Therefore, there is an urgent need to identify the provenance and production method of the mullet roes. In this study, we conducted a molecular phylogenetic analysis so as to identify the species and geographical origin of the mullet roes and we used stable isotopic values as a tool to differentiate between the wild-caught and farmed mullet roes. DNA sequence variations of a mitochondrial COI gene from the sampled mullets and mullet roes of wild-caught and farmed individuals, as well as the roe products sold in retail stores in Taiwan, were analyzed within the phylogenetic framework. The results showed that the samples were from four M. cephalus lineages (or putative Mugil species B, C, I, and H) occurring in the Caribbean Sea, Northwestern Pacific, and Southeastern Australia, and the M. liza in the Western Atlantic, respectively. The M. liza samples were from the salted roe products purchased from two retail stores, in which one claimed that the roes were imported from Brazil, whereas the other claimed that the roes were from locally reared flathead grey mullets. The farmed mullet roes had significantly lower δ13C values and less variation in δ15N values when compared with the wild-caught and imported mullet roes. Quadratic discriminant analysis based on the δ13C and δ15N values successfully discriminated the farmed mullet roes from the wild-caught and imported roes with an approximate error rate of 2%. Our study demonstrated that the combined approach of genetic and stable isotopic analyses can effectively authenticate the mullet roe origin and production methods.