You might think you know what's on your plate, but a three-year DNA survey of Bulgarian seafood reveals that over ten percent of products are mislabeled. This study exposes how economic fraud and labeling gaps threaten consumer trust in the supply chain.

Globalization and complex supply chains create opportunities for deceptive behaviors like mislabeling and economically motivated species substitutions. These fraudulent incidents can cause economic damage to consumers and even pose health risks if toxic species or allergens are present.

Building on a previous pilot study, this research conducted a three-year survey across four cities to assess the authenticity of five distinct taxonomic classes. Researchers used molecular identification via DNA barcoding and PCR-RFLP to verify if labeled species matched the actual product.

From March 2019 to July 2021, the team collected 199 seafood products from large retailers in Stara Zagora, Shumen, Varna, and Dobrich. White fish made up the largest portion of the sample at over fifty percent, reflecting their weight on the national market. Figure 1 breaks down the number of seafood products collected at retail outlets by taxonomical class, revealing a fairly limited variety of species available to consumers.

The chart highlights that fish and crustaceans represent the largest groups with one hundred and thirty-eight samples respectively, while gastropods are the least represented with only five. Green bars identify the most commonly encountered species within each group, such as Gadus chalcogrammus in fish, illustrating which specific varieties dominate the market.

For species identification, the researchers primarily targeted a fragment of the Cytochrome C oxidase subunit I gene, known as COI. When COI failed to identify a species, additional mitochondrial and nuclear genes were analyzed to enhance discriminatory ability. Table 1 outlines the specific molecular targets and amplification protocols used to identify various aquatic species, ranging from whitefish to crustaceans.

The authors detail distinct primer sequences and thermal cycling conditions for each taxonomic group, such as using an annealing temperature of 55 degrees Celsius for whitefish versus 47 degrees Celsius for bivalve mollusks. By standardizing these parameters across elective and additional genetic markers like COI and cytb, the study ensures precise DNA amplification necessary for accurate species allocation.

DNA extraction was successful for all 199 products, and sequencing allowed for species allocation in ninety-four point five percent of cases. Failures in identification were often due to low resolution of reference sequences or the absence of data for certain species.

Figure 3 displays the results of a PCR-RFLP analysis used to identify thirteen Mytilus sp. products that were initially ambiguous. The gel image shows DNA fragments separated by size after digestion with the Aci-I enzyme, where specific banding patterns allow for species-level differentiation.

For example, samples labeled as M. chilensis consistently show a single band at one hundred twenty-three base pairs, while those identified as M. galloprovincialis display two distinct bands at seventy-seven and forty-six base pairs.

This visual evidence confirms the utility of this method in resolving species identity when standard sequencing alone is insufficient. Comparing molecular results with labels revealed twenty-two substitutions out of 199 products, resulting in an overall mislabeling rate of eleven percent.

White fish showed the highest mislabeling rate at fourteen percent, followed by bivalve mollusks at twelve point five percent. Table 2 details the specific instances of mislabeling found within the whitefish category, where a substitution rate of fourteen percent was observed across one hundred samples.

The table contrasts the declared scientific names on product labels with the actual species identified through molecular barcoding, revealing that products labeled as Atlantic cod or Alaska pollock were frequently substituted with other species like Saithe or various hakes.

By listing the FAO distribution areas for both the claimed and real species, the authors highlight how these substitutions often involve fish from different geographical regions. The study suggests that some fraud occurs at the first sale level where species share geographic areas, while other substitutions happen later during processing.

Substitutions involving geographically distant species could also be attempts to conceal illegal fishing activities. This table compares the scientific names found on product labels against two official regulatory lists: Ordinance No. 4 from 2006 and the updated Ordinance No.

13 from 2021. The authors use this comparison to highlight a significant gap between the species actually present in the market and those officially recognized by law at the time of sampling. For instance, while *Gadus morhua* was accepted under the older ordinance, it is absent from the current list, whereas *Rapana venosa* appears only in the most recent update.

This discrepancy suggests that the existing regulations were ineffective at describing the actual basket of seafood available for sale. The authors conclude that implementing DNA-based monitoring systems is necessary to reduce involuntary substitutions and prevent deceptive practices.

Furthermore, the study confirms that the official list of commercial designations requires further updates to match the expanding variety of products sold. The study proves that DNA-based authentication is essential to catch species substitutions, while also highlighting an urgent need to update official trade name lists to match the reality of imported seafood.