Tuna or Foul? Investigating the Authenticity of “Maguro” Sushi with DNA Sequencing

Image credit: Dave Conklin: What is Sashimi? Essential Dining Guide to Japan’s Famous ‘Raw Seafood’

Introduction

Sushi’s global rise in popularity has brought attention to a pressing concern: seafood mislabeling. Studies reveal that cheaper fish are often substituted for premium species, raising questions about food fraud, health risks, and environmental sustainability. Mislabeling may mask overharvested species or introduce hazardous fish, such as escolar, which can cause digestive issues. Authenticity in labeling ensures consumer safety and environmental responsibility, especially when species like bluefin tuna, prized but endangered, are involved. In this study, we tested the authenticity of “Maguro” (tuna) sashimi served at a sushi bar using DNA sequencing. By comparing the DNA sequences of the sample to known reference sequences, we aimed to uncover whether the sashimi matched the advertised species.

Materials and Methods

Sample Collection and DNA Extraction: A tissue sample from the “Maguro” sashimi plate was preserved for analysis. DNA extraction was followed by PCR amplification. Primer Design: Primers were designed using NCBI Primer-BLAST with strict parameters for product size, melting temperature, and organism specificity. Primer 10 was selected for its optimal properties and likelihood to amplify the DNA efficiently. Sequence Matching: The amplified DNA underwent BLASTn analysis using the NCBI GenBank database to identify species matches based on sequence similarity.

Results

The BLASTn analysis revealed that the “Maguro” sashimi was not tuna but tilapia species: Oreochromis niloticus (Nile tilapia) with 100% identity and Oreochromis aureus (blue tilapia) with 98.59% identity. No other species matched the sample DNA, as shown in the picture and Table 1.0 below. This mislabeling raises significant concerns, as tilapia and tuna differ vastly in price, taste, and culinary applications.

Result of Sequence Blastn analysis from www.blast.ncbi.nlm.nih.gov

Table 1.0: Species Match Results

Species	Percent_Identity
Oreochromis niloticus	100.00
Oreochromis aureus	98.59

Discussion

The findings demonstrate clear mislabeling of the “Maguro” sashimi. Tilapia, a less expensive and readily available fish, was substituted for tuna—a premium seafood. This substitution misleads consumers, compromises trust, and violates food labeling regulations. From a public health perspective, mislabeling can mask risks, including exposure to allergens or toxins. Additionally, it undermines conservation efforts for overfished species like tuna. These results emphasize the importance of regulatory oversight and consumer education to combat seafood fraud.

Conclusion

This study highlights the efficacy of DNA sequencing and BLAST analysis in uncovering seafood mislabeling. The identification of tilapia as a substitute for tuna underscores the need for transparency and stricter regulations in the seafood industry. Future research with larger sample sizes and diverse genetic markers can further illuminate the prevalence of this issue and aid in its mitigation. Note:This article is intended for educational purposes.It`s based on my knowledge gained from Bioinformatics and not from actual laboratory findings.

References

Hebert, P. D. N., et al. (2003). Biological identifications through DNA barcodes. Proceedings of the Royal Society B.
Ryburn, S. J., et al. (2022). Public awareness of seafood mislabeling. PeerJ.
Wong, E. H., & Hanner, R. H. (2008). DNA barcoding detects market substitution. Food Research International.

Author: Philip Yamoah Appiah, MSc. Health Data Science
School: The George Washington University, Milken Institute of Public Health

LinkIn: www.linkedin.com/in/philip-appiah-855b91188 Email : pyappiah561@gmail.com