Gonzalo Machado-Schiaffino

High Level of Mislabeling in Spanish and Greek Hake Markets Suggests the Fraudulent Introduction of African Species

DNA analysis of hake products commercialized in southern European (Spanish and Greek) market chains have demonstrated more than 30% mislabeling, on the basis of species substitution. Tails and fillets were more mislabeled than other products, such as slices and whole pieces. African species were substitute species for products labeled as American and European species, and we suggest it is a case of deliberate economically profitable mislabeling because real market prices of European and American hake products are higher than those of African in Spanish market chains. The presented results suggest fraud detection that disadvantages African producers. Government-mandated genetic surveys of commercial hakes and the use of subsequent statements of fair trade on labels of seafood products could help to reduce fraud levels in a global market of increasingly conscious consumers sensitive to ethical issues.

Molecular Organization and Evolution of 5S rDNA in the Genus Merluccius and Their Phylogenetic Implications

The molecular organization of the 5S rRNA gene family has been studied in a wide variety of animal taxa, including many bony fish species. It is arranged in tandemly repeated units consisting of a highly conserved 120 base pair–long region, which encodes for the 5S rRNA, and a nontranscribed spacer (NTS) of variable length, which contains regulatory elements for the transcription of the coding sequence. In this work, a comparative analysis of 5S ribosomal DNA (rDNA) organization and evolution in the 12 species of the genus Merluccius, which are distributed in the Atlantic and Pacific oceans, was carried out. Two main types of 5S rDNA (types A and M) were identified, as differentiated by the absence or presence of a simple sequence repeat within the NTS. Four species exhibited the 2 types of 5S rDNA, whereas the rest showed only 1 type. In addition, the species M. albidus and M. bilinearis showed 2 variants (S and L) of type-M 5S rDNA, which differentiated by length. The results obtained here support the hypothesis of a 5S rRNA dual system as an ancient condition of the Piscine genome. In contrast, some inconsistencies were found between the phylogeny of the genus Merluccius based on mitochondrial genes and that obtained from nuclear markers (5S rDNA, microsatellite loci, and allozyme data). Hybrid origin of the American species M. australis is suggested based on these results.

Detection of Mislabeling in Hake Seafood Employing mtSNPs-Based Methodology with Identification of Eleven Hake Species of the Genus Merluccius

Species-specific DNA-based tags are valuable tools for the management of both fisheries and commercial fish products. Eleven hake species of the genus Merluccius have been identified employing mtSNPs-based methodology. The method is highly reproducible, fast, and technically easy. It is a reliable tool, allowing for routine analysis of commercial seafood. It can be applied by nonexperts in genetics because both laboratory handling and interpretation of results are easy and direct. The convenience of routine surveys in fish markets has been clearly established with a survey of commercial hake batches imported in south Europe. A total of 40 commercial processed hake were analyzed in this study. More than 20% of mislabeling has been detected.

Introgressive hybridization in North American hakes after secondary contact.

High levels of bidirectional introgressive hybridization were found between the two Atlantic North American hakes Merluccius albidus and M. bilinearis in their overlapping distribution area between the 34 and the 42 degrees N parallels, employing mitochondrial and nuclear DNA markers. Absence of F(1) hybrids, and varied levels of bidirectional introgression, indicate long-time hybridization and backcrossing. Based on the evolutionary history of the genus Merluccius, originated in this area from the ancestor of the present M. bilinearis by the rise of the Panama Isthmus, secondary contact between the two species has probably been promoted by northwards displacement of M. albidus. Higher introgression rates in southern areas of M. albidus could be explained by restricted gene flow in that area which may allow long-term accumulation of introgressed genes.

Strong genetic differentiation of the Austral hake (Merluccius australis) across the species range.

Population structuring of marine organisms is not always easily understood. In open marine areas without apparent barriers to migration, species with high dispersal capacity are expected to be organized in large populations that, ideally, could represent the best example of panmictic units more or less genetically homogeneous. However, there are a number of examples contradicting this panmixia theory. In some cases, physical barriers like straits (e.g. the Gibraltar Strait separating Mediterranean and Atlantic populations, see a review in Patarnello et al. (2007)) or currents (e.g. the East Australian Current for sea urchin (Banks et al., 2007)) can be identified as obstacles for population homogenization across a species range. As there is much variation in DNA markers which is easily detected, there has been a growing interest in their application to better understand population structuring. Microsatellite loci, for example, can detect weak differentiation in species with high gene flow (Waples, 1998). On the other hand, large-scale geographical differences are better detected employing mitochondrial DNA polymorphisms because, due to maternal inheritance, effective population size for mtDNA is a quarter of that of nuclear genes, and consequently genetic drift may produce higher population differentiation (Birky et al., 1989). Therefore combining nuclear and mitochondrial loci is a good strategy for detecting even weak regional differences in population structure.

Mislabeling of Two Commercial North American Hake Species Suggests Underreported Exploitation of Offshore Hake

Abstract Mislabeling of North American merlucciid hakes in stock surveys and commercial market samples was detected by employing nuclear 5S ribosomal DNA (rDNA) and mitochondrial cytochrome b variation as molecular markers. Results showed that offshore hake Merluccius albidus is sold in European markets but is labeled as the morphologically similar silver hake M. bilinearis, which is the target species of the fishery. This suggests that offshore hake may be inadvertently included within silver hake landings, as the two species overlap in the southern area of silver hake distribution (approximately 41°-35°N latitude near North American coasts). An inexpensive and technically easy technique based on polymerase chain reaction (PCR) amplification of a fragment of 5S rDNA and visualization of PCR products in agarose gels is recommended for routine species assignation in landings for purposes of exploitation estimates and for authentication of commercial hake species.

Atlantic Salmon at Risk: Apparent Rapid Declines in Effective Population Size in Southern European Populations

Abstract Populations of southern European Atlantic salmon Salmo salar are subjected to exploitation by sportfishing and exhibit evidence of dramatic catch reduction for the same fishing effort over recent history. We employed nine microsatellite loci as markers to estimate effective population sizes of Atlantic salmon in five rivers of northern Spain for comparison with 1990s data describing the same populations; marked declines in effective population sizes over the last decade were detected, and a reduced census size is proposed to be one of the probable causes. These estimates highlight the endangered status of the Atlantic salmon populations in northern Spain. A reduction in fishing effort and an increase in protective measures are recommended for the conservation of these fragile populations at the southernmost edge of the species’ natural distribution.

Use of multiple markers demonstrates a cryptic western refugium and postglacial colonisation routes of Atlantic salmon ( Salmo salar L.) in northwest Europe

Glacial and postglacial processes are known to be important determinants of contemporary population structuring for many species. In Europe, refugia in the Italian, Balkan and Iberian peninsulas are believed to be the main sources of species colonising northern Europe after the glacial retreat; however, there is increasing evidence of small, cryptic refugia existing north of these for many cold-tolerant species. This study examined the glacial history of Atlantic salmon in western Europe using two independent classes of molecular markers, microsatellites (nuclear) and mitochondrial DNA variation. Alongside the well-documented refuge in the Iberian Peninsula, evidence for a cryptic refuge in northwest France is also presented. Critically, methods utilised to estimate divergence times between the refugia indicated that salmon in these two regions had diverged a long time before the last glacial maximum; coalescence analysis (as implemented in the program IMa2) estimated divergence times at around 60 000 years before present. Through the examination of haplotype frequencies, previously glaciated areas of northwest Europe, that is, Britain and Ireland, appear to have been colonised from salmon expanding out of both refugia, with the southwest of England being the primary contact zone and exhibiting the highest genetic diversity.

A microsatellite baseline for genetic stock identification of European Atlantic salmon (Salmo salar L.)

This work forms part of the SALSEA-Merge research project (Project No. 212529) and was funded by the European Union under theme six of the Seventh Framework programme. It was also co-sponsored by the Atlantic Salmon Trust and the Total Foundation, who we thank for financial support. PMcG and JC were partly supported by the Beaufort Marine Research Award in Fish Population Genetics funded by the Irish Government under the Sea Change Programme. The work was also supported under financial support of the program of fundamental research of Presidium of RAS “Searching fundamental scientific investigations in the interests of development of the Arctic zone of Russian Federation.”

Long-term effects of stock transfers: synergistic introgression of allochthonous genomes in salmonids

The genus Salmo was employed as a model to study introgression of genes between species due to secondary contacts. Seven microsatellite loci, the LDH-C1* locus and the 5S ribosomal DNA were studied. Results showed the mutually enhanced introgression of allochthonous genomes into southern European salmonids. This phenomenon appears to go beyond a simple consequence of the altered behaviour of domestic individuals. Invasions of autochthonous genomes by allochthonous genes would be enhanced by human activities such as stock transfers, which would simultaneously promote allochthonous and allospecific (from other species) introgressions in a synergistic process in Atlantic salmon Salmo salar and brown trout Salmo trutta. As a minor result, the data do not support the value of the microsatellite locus SsaD486 as a species-specific marker.