Detection of hybridization and introgression in wild populations that have been supplemented by hatchery fish is necessary during development of conservation and management strategies. Initially, allozyme data and more recently highly polymorphic microsatellite markers have been used to obtain this information. We used both markers to assess the effectiveness of four assignment methods (STRUCTURE, NEWHYBRIDS, BAPS and GeneClass) to detect hatchery introgression in wild stocked populations. Simulations of hybrid genotypes from real parental data revealed that the number and type of markers used with STRUCTURE, NEWHYBRIDS and BAPS can identify as admixed most first and second generation hybrids as well as first generation backcrosses. In wild populations, introgression rates estimated from different markers and methods were correlated. However, slight disagreements were observed at both population and individual levels. Overall, the fully Bayesian (STRUCTURE, NEWHYBRIDS and BAPS) performed better than partially Bayesian (GeneClass) assignment tests. In wild collections, BAPS analyses were limited because of the lack of a native baseline. In all cases, the efficiency of methods was reduced as introgression increased.

Five qualitative and seven quantitative colouration and spotting pattern features were measured in 23 brown trout Salmo trutta populations and two hatchery stocks. Simultaneously, the LDH-C1*, a diagnostic locus fixed for *90 and *100 alleles in stocking and native populations from southern Europe, respectively, was analysed to classify the brown trout studied according to their origin: native, hatchery stock and hybrids. The three genotypes showed significant differences in the colouration and spotting features and a discriminant function analysis could correctly identify 79% of the individuals. The most discriminating variables were dorsal fin margin colour, number of opercular spots, presence of the preopercular mark and diameter of black spots. Given the low cost, ease and possibility of field identification of native fish, the results indicate great opportunities for the application of morphological-based classification models on the conservation and management of native brown trout stocks. # 2005 The Fisheries Society of the British Isles

Genetic changes in the population structure of brown trout Salmo trutta in the eastern Pyrenees were monitored during the 1990s. Stocking with cultivated exogenous fish has resulted in introgressed populations where those with higher introgression coefficients also have the highest values of heterozygosity. Nevertheless, this increase of local diversity reflects a decrease of genetic differentiation between populations and loss of native alleles. These changes obscure native gene pools and modify evolutionary distinctions among native brown trout populations. # 2004 The Fisheries Society of the British Isles

The Atlantic bluefin tuna (Thunnus thynnus) is an extraordinary fish that has amazed humanity since ancient times. However, the continuous overexploitation of this fishery, particularly in the Mediterranean Sea, could result in a total collapse of this resource. Currently, this species is managed as two stocks: Western Atlantic and Mediterranean-Eastern Atlantic, with a recognized genetic differentiation between them. On the other hand, the population structure within the Mediterranean Sea is still unclear. The biological data supports the idea of two separate populations in the eastern and western Mediterranean basins. However, nuclear microsatellite and mitochondrial DNA (mtDNA) analyses of two samples representative of these two basins result in a lack of heterogeneity. A comparison of these results with previously published studies reveals some discrepancies. We have compared 59 genetic differentiation tests that include samples within the Mediterranean. Of these, about 60% gave significant differentiation while the remaining 40% were non-significant. But, when only nuclear-based loci were considered, genetic differentiation was detected in up to 73% of the cases with an average significant F ST of only 0.018, whereas the average significant F ST of the mtDNA-based studies was significantly higher (0.029). However, in some cases, it is difficult to reconcile the biology of the species with the results suggesting genetic differentiation. In conclusion, although it is not yet possible to reach a definitive conclusion about the population structure, but considering all biological and genetic data, we suggest an independent management approach for each basin to avoid the impact of a type II error that could lead to the possible loss of the regional subpopulations.

The Asian clam (Corbicula sp.) is an invasive freshwater bivalve native to Asia, the Middle East, Australia, and Africa. It is now widely distributed around the world producing large ecological and economic impacts. Three well-described invasive lineages form a cryptic species complex with asexual reproduction based on androgenesis. In this study, we collected 175 individuals from different Iberian, European, and North American locations to genetically study Corbicula invasion in the Iberian Peninsula using COI and 28S genes. The use of mitochondrial and nuclear markers allows us to characterize both maternal and paternal inheritance from androgenetic Corbicula locations and to deal with the incongruences caused by egg parasitism. We identified 7 COI and 10 28S haplotypes that grouped individuals within the three invasive Corbicula lineages. Haplotype distribution of mitochondrial and nuclear markers detected genetic divergence between the Ebro Delta location and the rest of Iberian sites, suggesting that at least two invasion episodes occurred in the Iberian Peninsula. Haplotype distribution also suggested secondary contacts between Iberian and other European invaded regions. Additionally, results revealed that nuclear hybridization, a feature more widespread than previously reported, contributes to retain gene diversity in the Corbicula invasionThis research was carried out within the objectives of the research project CGL200909407 of the Spanish Ministerio de Ciencia e Innovacio´n (MICINN). LP received a PhD fellowship support of the Spanish MICINN with reference BES—201003744

–  Management policies balancing harvest and conservation of natural populations of fish are difficult to establish, both scientifically and politically. This issue is particularly difficult when those populations represent native genetic resources. Since 1997, several brown trout populations in the eastern Pyrenees Mountains (Spain) were designated as ‘genetic refuges’ under varying fishing regulations, where releases of hatchery‐origin fish are not permitted. We analysed genetic variation in samples of brown trout from six of those refuge populations and four non‐refuge populations within the same region. Each population was sampled in four separate years: 1993, 1999, 2004 and 2006. Our analyses were based on a diagnostic allele (LDH‐C*90) that distinguishes native and exogenous hatchery populations. Comparisons were based on stocking histories before and after refuge designations and on three management strategies: fished, unfished and catch‐and‐release. Overall, we detected significant genetic introgression resulting from past stocking practices despite the current restriction of hatchery releases imposed by the recent genetic refuge policy. However, this new policy has prevented detectable introgression from increasing throughout the region and together with additional measures on length and number of captured fish is contributing to self‐sustained fisheries that are achieving conservation goals. Quick acceptance of ‘genetic refuges’ by anglers in one particular river, the Ter River basin, has been a key factor in protecting native gene pools compared with the Segre River basins where refuges were not readily accepted.

1. The three-spined stickleback (Gasterosteus aculeatus) on the Iberian Peninsula is only distributed in freshwater habitats and has completely disappeared from most of its range, mainly as a consequence of habitat degradation and invasive fish introductions. Genetic investigations have shown that Mediterranean-Adriatic sticklebacks constitute an evolutionarily significant unit. Here, we present the first genetic data for Iberian populations living on the southern edge of the stickleback's range. We used microsatellite markers to study gene diversity, population structure and genetic demography of stickleback populations. 2. High genetic differentiation among collections yielded a model of four genetically homogeneous units related to geography. The observed pattern of isolation by distance resulted mainly from the hydrographical pattern and limited gene flow among rivers. Moreover, low levels of gene diversity, high isolation and recent bottleneck events, which have led to small or even critical effective population sizes in several locations, could be explained by additional recent anthropogenic fragmentation. 3. We defined at least four evolutionarily significant units threatened by habitat fragmentation in north-eastern Iberian sticklebacks. Because they retain long evolutionary histories, these populations should be considered of high conservation priority, and urgent management measures should be implemented.

Viñas, J., Sanz, N., Peñarrubia, L., Araguas, R-M., García-Marín, J-L., Roldán, M-I., and Pla, C. 2014. Genetic population structure of European anchovy in the Mediterranean Sea and the Northeast Atlantic Ocean using sequence analysis of the mitochondrial DNA control region. – ICES Journal of Marine Science, 71: 391–397. The European anchovy (Engraulis encrasicolus) exhibits a complex population structure in the Mediterranean Sea and Northeast Atlantic Ocean. To resolve the population genetic structure of this species, we surveyed sequence variability in the mitochondrial (mtDNA) control region in samples (n = 563) from 13 locations in the Northeast Atlantic, the Bay of Biscay, and the Mediterranean Sea. Based on pairwise ΦSTs, SAMOVA, and multidimensional scaling, a complicated population structure composed of multiple populations emerged. Combining these results with those from previous population studies based on mitochondrial and nuclear markers, we identified nine genetically differentiated European anchovy populations: (i) Canary Islands; (ii) Cádiz; (iii) Alborán Sea; (iv) Garona; (v) Arcachon and Donostia; (vi) a large population in the northwestern Mediterranean, including Cadaqués, Gulf of Lyon, Elba, and Sicily; (vii) southern Adriatic; (viii) northern Adriatic; and (ix) Aegean Sea. We suggest that independent management strategies should be implemented for each genetically differentiated population, and, in cases where several fisheries stocks are recognized within an area of genetic homogeneity, each stock should be managed separately.