Juliana Perez

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.

Genetic identification of nine hake species for detection of commercial fraud.

This study describes the 5S rRNA gene as a simple and reliable one-step PCR-based genetic marker that allows unambiguous identification of Merluccius paradoxus, Merluccius senegalensis, Merluccius australis, Merluccius gayi, Merluccius bilinearis, Merluccius hubbsi, and Macruronus magellanicus. The marker is based on differences in length at the nontranscribed spacer within the 5S rRNA genes and is robust enough for identification of processed products, such as fish fingers and other precooked commercial hake. Further restriction fragment length polymorphism analysis at the mitochondrial cytochrome b gene can distinguish Merluccius merluccius and Merluccius capensis. The application of these markers for routine works such as surveys of quality and labeling of commercial hakes is suggested due to their accuracy, low price, and possible automation for large-scale surveys.

Cloning and physical mapping of Atlantic salmon (Salmo salar L.) telomeric sequences

We cloned and sequenced DNA containing telomeric sequences from Atlantic salmon (Salmo salar L.). At both low and high stringency conditions, a cloned probe containing (TTAGGG)n sequences binds only at the extreme termini of the chromosomes, not at interstitial sites. Blocks of interstitial telomere-like sequences were expected from the chromosome polymorphism because of Robertsonian translocations that exist in Atlantic salmon. Our results support the hypothesis that telomeric sequences were almost entirely lost during chromosome fusion events.

The malic enzyme MEP-2* locus in Spanish populations of Atlantic salmon: Sea age and foreign stocking

Abstract: Wild Spanish populations of Salmo salar were analyzed for their variability at the MEP-2* locus that determines the malic enzyme expressed in muscle mitochondria. The allele frequencies of these populations have been found to be associated with sea-age of returning adults and freshwater temperature; in a minor extent with foreign stocking of Irish and Scottish alevins; and finally, no association was found with precocious parr maturation.

Interspecific hybridization, a matter of pioneering? Insights from Atlantic salmon and brown trout.

Interspecific hybridization may occur in situations of recent contact between a colonizer and a resident species, being more intense in the colonization front. Atlantic salmon Salmo salar and brown trout S. trutta have been sympatric species since their origin and they share spatial and temporal spawning niches, exhibiting low levels of bidirectional interspecific hybridization and introgression throughout their distribution range. Different causes have been identified for increased hybridization, from escapes or deliberate releases of domesticated fish to sneaking male behavior. We have examined hybridization rates and direction in different situations of advance of one of these species into a territory formerly inhabited by the other (247 samples were analyzed in northern Spain and 487 in Kerguelen Islands). In all cases, hybrids found in the colonization front were offspring of colonizer females and resident males. We hypothesize that these findings are the result of adaptive relaxed mate choice of colonizing females, regardless of the relative abundance of each species.

Physical localization and characterization of the BglI element in the genomes of Atlantic salmon (Salmo salar L.) and brown trout (S. Trutta L.)

This work describes chromosomal localization, fine physical mapping, and population variation of the BglI element in the genome of Atlantic salmon (Salmo salar L.) and a similar sequence in the genome of brown trout (S. trutta L.). Results from a variety of complementary approaches, clearly demonstrate that the BglI element does not occur as a satellite-like repetitive DNA in these species but is part of the rDNA cistron as suggested by Goodier and Davidson (1993). Coincident hybridization of BglI clones with rDNA loci in both single and double-probe fluorescence in situ hybridization (FISH) experiments demonstrated physical linkage between the BglI element and rDNA loci. Fine physical mapping by Southern analysis and PCR amplification showed the BglI element to be located approximately 1.6 kb upstream of the 18S gene. The BglI element was used to screen for population-specific markers by Southern analysis. Population-specific banding patterns were only observed in brown trout, allowing identification of individual populations of this species. Sequence comparisons revealed sequences similar to the BglI element present in the rDNA cistron of other salmonids. This result suggests the presence of this sequence in the genome of the salmonid tetraploid ancestor.

Interspecific introgression and changes in population structure in a flatfish species complex after the Prestige accident

Oil spills cause aggressive impacts on marine ecosystems affecting immense areas and the species inhabiting them. If wastes are not cleaned up properly, the remnants may affect local populations for a long time. This work focuses on the long-term impacts of the Prestige spillage that occurred off Galician coast (Spain) in November 2002. Model species were two sympatric flatfish, the megrims Lepidorhombus whiffiagonis and Lepidorhombus boscii. Samples obtained before and nine years after the Prestige accident from affected and unaffected areas were genotyped for six hypervariable nuclear markers and for the mitochondrial D-loop sequence. The results revealed a high proportion of post-F1 interspecific hybrids in the area affected, and also increased intraspecific population differentiation likely due to such localized introgression of foreign genes. These changes suggest the appearance of a hybrid zone following the accident and emphasize the need of paying special attention to potential evolutionary impacts of oil spills.