As part of the Labelfish Project’s work to broaden interest in, and deepen the knowledge of, stakeholders in seafood labelling, traceability and molecular techniques, please find below the first edition of a series of brief reviews of papers in the area. These papers are salient works in terms of their recency or their importance to the area of conservation genetics.
Lago, Fatima C.; Vieites, Juan M. & Espineira, Montserrat (2013). Authentication of gadoids from highly processed products susceptible to include species mixtures by means of DNA sequencing methods. Eur. Food Res. Technol., 236:171-180.
This paper is on the development of a DNA-based method to identify 15 gadoid species in food products, even in highly processed products, and moreover, even in mixture. The developed tool is based on the amplification of a 464 bp fragment of the cyt b gene and an internal fragment of 263 bp for identification the highly processed products, and subsequent phylogenetic analysis (FINS: Forensically Informative Nucleotide Sequencing methodology). The authors have designed a specific method for the detection of the mixture of 3 Gadus species (G. morhua, G. macrocephalus and G. ogac – these 3 gadoids are the most similar species both morphologically and genetically) based on 14 SNP (single nucleotide polymorphism). If the mixture is with other species, the genetic difference would be detected by the appearance of numerous double peaks in the chromatograms of sequencing. The method was validated both on processed products made in a pilot plant and on 25 commercial products.
This paper proposes an interesting methodology to identify the main gadoid species which are one of the most important commercial species throughout the world. Nevertheless, the detection of the mixtures is based on a thorough knowledge of the users of the targeted cyt b fragment sequences and it requires to have access in the laboratory to validated reference sequences.
Griffiths, A. M., Miller, D. D., Egan, A., Fox, J., Greenfield, A., & Mariani, S. (2013). DNA barcoding unveils skate (Chondrichthyes: Rajidae) species diversity in ‘ray’products sold across Ireland and the UK. PeerJ, 1, e129 that is available from the open access journal PeerJ at the following URL: https://peerj.com/articles/129/.
This work uses DNA barcoding to identify species of skates sold under the commercial term of ray wings and demonstrates some of the potential uses for DNA identification of fish species in a conservation context. Within Europe a number of skate species have declined so severely that it is now prohibited to land them, but species identification by DNA testing remains the only method to investigate exactly what is being sold to consumers. In what is great news for conservation of these declining species, none of those which are prohibited were identified in the 99 samples we analysed. However, several potentially vulnerable species were identified, including those that marine conservation organisations suggest should not be purchased by consumers, over concerns regarding their ability to recover from fisheries pressures.
This paper is one of an important group that demonstrate how powerful DNA based methods can be for the conservation of vulnerable elasmobranchs, as other publications have demonstrated endangered species in illegal catches seized by authorities, investigated the damaging trade in shark-fins and shown mislabelling of shark products.
Di Pinto, A., Pietro Di Pinto, Terio, V., Bozzo, G., Bonerba, E., Ceci, E., & Tantillo, G. (2013). DNA barcoding for detecting market substitution in salted cod fillets and battered cod chunks. Food Chemistry, 141(3), 1757–1762.
This paper describes the application of COI as DNA marker for practical identification of species in comercial samples of cod products marketed in Italy.
COI sequences permited the identification of 65 samples from a total of 70 (93% of samples), 85% of the samples belonged to Gadidae family whereas the other 15% were species of the Lotidae family. 76% of salted cod products were correctly labeled as cod (they contained G. morhua or G. macrocephalus). In the case of battered cod products the level of mislabelling was 70%. Taking together the results for salted cod and battered products, the level of mislabelling was of 56%. Authors show in the study that the main species involved in fraudulent substitutions were Pollachius virens and Brosme brosme, much cheaper species than the two Gadus species. Also, there is a difference in mislabelling in the two types of products, mislabelling is lower in salted cod, whereas battered cod presented a higher mislabelling level. Authors relate this fact with greater difficulty of visually identifying morphological characteristics in chunks, they also state that there are very little differences in taste or texture among species in this type of product, so the substitution is more easy to hide.
Boukouvala, E., Cariani, A., Maes, G. E., Sevilla, R. G., Verrez-Bagnis, V., Jérôme, M., Guarniero I Monios G, Tinti F, Volckaert F, Bautista J.M. & Krey, G. (2012). Restriction fragment length analysis of the cytochrome b gene and muscle fatty acid composition differentiate the cryptic flatfish species Soleasolea and Soleaaegyptiaca. Journal of agricultural and food chemistry, 60(32), 7941-7948.
This paper deals with the development of a simple, rapid and cost-efficient restriction fragment length-based diagnostic test that differentiates common sole (Soleasolea) from Egyptian sole (Soleaaegyptiaca) and other Soleidae-species. This is interesting as the common sole is a fish of high commercial value and is often substituted – fraudulently or unintentionally – with species of lower value. The paper shows that the common solelives in sympatry with S. aegyptiaca in areas of the Mediterranean Sea and both species have overlapping external morphometric characters, which can lead to misidentifications and unintentional substitutions of S. solea with S. aegyptiaca. The paper also demonstrates that the common sole has a higher level of total polyunsaturated fatty acidsand lower level of total saturated fatty acids in white muscle compared to S. aegyptiacaand thus may be of better nutrition value. Furthermore, the paper indicates that the differences in fatty acid composition can also be used to differentiate the two species but more samples must be analyzed to verify this model.
Miller, D., Jessel, A. & Mariani, S. (2012) Seafood mislabelling: comparisons of two western European case studies assist in defining influencing factors, mechanisms and motives. Fish and Fisheries 13, 345-358.
The study discussed in this paper looks at the level of cod mislabelling in the UK and Ireland. Samples of cod, the most popular whitefish in both Ireland and the UK, included fresh, frozen, smoked, breaded and battered specimens. The results showed that there was a significantly higher level of cod mislabelling in Ireland compared to the UK (28.2% vs 7.4%). In Ireland a high proportion of the mislabelled cod was smoked (70.3%), whereas none of the mislabelled cod products in the UK were smoked. There also appears to be an issue with breaded and battered products sold in Ireland with 28.4% of these mislabelled, compared with 9.4% in the UK. The authors suggest that the reason why there is a higher level of cod mislabelling in Ireland is related to consumer awareness, with a higher number of environmental non-government organisations and campaigns in the UK used to raise public awareness. It is also suggested that the higher level of awareness in the UK may explain the greater amount of detail available on UK cod product labels.
The substitution of cheaper white fish for cod shows obvious financial motivation for those involved. However, consumers do not know what they are buying or if it is sustainably sourced. The study found that in several cases the sample was labelled as being Pacific cod but was actually identified as Atlantic cod. Although the reason for this substitution is not as clear, it is suggested that illegal, unreported and unregulated fishing may be to blame. Consumers who are aware of the depleting Atlantic cod stocks may refrain from consuming it and may be more inclined to purchase Pacific cod as an alternative. As the authors note, mislabelling could lead to health risks, economic losses and changes in consumer purchasing habits, possibly leading to depletion of a species. Although this study was unable to determine where in the food-chain supply the mislabelling occurred, it highlights the need for enforcement of legislation and the introductions of systems to check labelling authenticity.