Comparison of maturation timing,egg size and fecundity between hatchery lines of chinook salmon and their wild donor stocks

Increasing concern has been expressed about the genetic effects of cultured salmonid fishes on natural populations. Avoidance of extreme negative outcomes was one reason for the establishment of a genetic management policy for the State of Alaska. However, domestication within the hatchery may still cause divergence from the wild donor population. This divergence could potentially lead to adverse impacts on wild stocks through straying and introgression. This study examines potential domestication in two Alaskan chinook salmon stocks. The Little Port Walter (LPW) Hatchery Chickamin River stock resulted from a small collection of wild broodstock in 1976. The LPW Unuk stock was founded with a larger number of individuals in 1976 and has had subsequent infusion of wild gametes. These lines have been maintained at LPW through ocean ranching of tagged smolts. Comparisons are made between the hatchery lines, progeny of wild chinook collected from the Chickamin and Unuk Rivers, and hybrids between the hatchery and wild groups. Mature ocean‐ranched female chinook salmon returning to the facility were periodically graded for ripeness and spawned. Body size and meristic measurements were collected from these mature spawners. Maturation timing, fecundity, and individual egg size of these fourth generation hatchery fish are compared with that of offspring of wild fish from the same donor stock. Stock of origin is confirmed for all spawners and offspring using microsatellite DNA analysis.     

Consequences to fitness‐related traits of hybridization between farmed and wild Atlantic salmon, Salmo salar

Increasing concern has been expressed about the genetic effects of cultured salmonid fishes on natural populations. Avoidance of extreme negative outcomes was one reason for the establishment of a genetic management policy for the State of Alaska. However, domestication within the hatchery may still cause divergence from the wild donor population. This divergence could potentially lead to adverse impacts on wild stocks through straying and introgression. This study examines potential domestication in two Alaskan chinook salmon stocks. The Little Port Walter (LPW) Hatchery Chickamin River stock resulted from a small collection of wild broodstock in 1976. The LPW Unuk stock was founded with a larger number of individuals in 1976 and has had subsequent infusion of wild gametes. These lines have been maintained at LPW through ocean ranching of tagged smolts. Comparisons are made between the hatchery lines, progeny of wild chinook collected from the Chickamin and Unuk Rivers, and hybrids between the hatchery and wild groups. Mature ocean‐ranched female chinook salmon returning to the facility were periodically graded for ripeness and spawned. Body size and meristic measurements were collected from these mature spawners. Maturation timing, fecundity, and individual egg size of these fourth generation hatchery fish are compared with that of offspring of wild fish from the same donor stock. Stock of origin is confirmed for all spawners and offspring using microsatellite DNA analysis.     

Managing polyploidy in ex situ conservation genetics: the case of the critically endangered Adriatic sturgeon (Acipenser naccarii)

While the current expansion of conservation genetics enables to address more efficiently the management of threatened species, alternative methods for genetic relatedness data analysis in polyploid species are necessary. Within this framework, we present a standardized and simple protocol specifically designed for polyploid species that can facilitate management of genetic diversity, as exemplified by the ex situ conservation program for the tetraploid Adriatic sturgeon Acipenser naccarii. A critically endangered endemic species of the Adriatic Sea tributaries, its persistence is strictly linked to the ex situ conservation of a single captive broodstock currently decimated to about 25 individuals, which represents the last remaining population of Adriatic sturgeon of certain wild origin. The genetic variability of three F1 broodstocks available as future breeders was estimated based on mitochondrial and microsatellite information and compared with the variability of the parental generation. Genetic data showed that the F1 stocks have only retained part of the genetic variation present in the original stock due to the few parent pairs used as founders. This prompts for the urgent improvement of the current F1 stocks by incorporating new founders that better represent the genetic diversity available. Following parental allocation based on band sharing values, we set up a user-friendly tool for selection of candidate breeders according to relatedness between all possible parent-pairs that secures the use of non-related individuals. The approach developed here could also be applied to other endangered tetraploid sturgeon species overexploited for caviar production, particularly in regions lacking proper infrastructure and/or expertise.     

Domestication and the distribution of genetic variation in wild and cultivated populations of the Mesoamerican fruit tree Spondias purpurea L. (Anacardiaceae)

Domestication occurs as humans select and cultivate wild plants in agricultural habitats. The amount and structure of variation in contemporary cultivated populations has been shaped, in part, by how genetic material was transferred from one cultivated generation to the next. In some cultivated tree species, domestication involved a shift from sexually reproducing wild populations to vegetatively propagated cultivated populations; however, little is known about how domestication has impacted variation in these species. We employed AFLP data to explore the amount, structure, and distribution of variation in clonally propagated domesticated populations and sexually reproducing wild populations of the Neotropical fruit tree, Spondias purpurea (Anacardiaceae). Cultivated populations from three different agricultural habitats were included: living fences, backyards, and orchards. AFLP data were analysed using measures of genetic diversity (% polymorphic loci, Shannon's diversity index, Nei's gene diversity, panmictic heterozygosity), population structure (F(ST) analogues), and principal components analyses. Levels of genetic variation in cultivated S. purpurea populations are significantly less than variation found in wild populations, although the amount of diversity varies in different agricultural habitats. Cultivated populations have a greater proportion of their genetic variability distributed among populations than wild populations. The genetic structure of backyard populations resembles that of wild populations, but living fence and orchard populations have 1/3 more variability distributed among populations, most likely a reflection of relative levels of vegetative reproduction. Finally, these results suggest that S. purpurea was domesticated in two distinct regions within Mesoamerica.     

Genetic monitoring of the Amazonian fish matrinchã (Brycon cephalus) using RAPD markers: insights into supportive breeding and conservation programmes

The importance of genetic evaluations in aquaculture programmes has been increased significantly not only to improve effectiveness of hatchery production but also to maintain genetic diversity. In the present study, wild and captive populations of a commercially important neotropical freshwater fish, Brycon cephalus (Amazonian matrinchã), were analyzed in order to evaluate the levels of genetic diversity in a breeding programme at a Brazilian research institute of tropical fish. Random Amplified Polymorphic DNA fingerprinting was used to access the genetic variability of a wild stock from the Amazon River and of three captive stocks that correspond to consecutive generations from the fishery culture. Although farmed stocks showed considerably lower genetic variation than the wild population, a significantly higher level of polymorphism was detected in the third hatchery generation. The results seem to reflect a common breeding practice on several hatchery fish programmes that use a small number of parents as broodstocks, obtaining reproductive success with few non‐identified mating couples. The obtained data were useful for discussing suitable strategies for the genetic management and biodiversity conservation of this species.     

Genetic diversity and population structure of wild olives from the North-Western Mediterranean assessed by SSR markers

BACKGROUND AND AIMS: This study examines the pattern of genetic variability and genetic relationships of wild olive (Olea europaea subsp. europaea var. sylvestris) populations in the north-western Mediterranean. Recent bottleneck events are also assessed and an investigation is made of the underlying population structure of the wild olive populations. METHODS: The genetic variation within and between 11 wild olive populations (171 individuals) was analysed with eight microsatellite markers. Conventional and Bayesian-based analyses were applied to infer genetic structure and define the number of gene pools in wild olive populations. KEY RESULTS: Bayesian model-based clustering identified four gene pools, which was in overall concordance with the Factorial Correspondence Analysis and Fitch-Margoliash tree. Two gene pools were predominantly found in southern Spain and Italian islands, respectively, in samples gathered from undisturbed forests of the typical Mediterranean climate. The other two gene pools were mostly detected in the north-eastern regions of Spain and in continental Italy and belong to the transition region between the temperate and Mediterranean climate zones. CONCLUSIONS: On the basis of these results, it can be assumed that the population structure of wild olives from the north-western Mediterranean partially reflects the evolutionary history of these populations, although hybridization between true oleasters and cultivated varieties in areas of close contact between the two forms must be assumed as well. The study indicates a degree of admixture in all the populations, and suggests some caution regarding genetic differentiation at the population level, making it difficult to identify clear-cut genetic boundaries between candidate areas containing either genuinely wild or feral germplasm.     

Comparison of genetic diversity at microsatellite loci and quantitative traits in hatchery populations of Japanese flounder Paralichthys olivaceus

Relationships of genetic diversity at microsatellite loci and quantitative traits were examined in hatchery-produced populations of Japanese flounder using a relatively straightforward experiment. Five hatchery populations produced by wild-caught and domesticated broodstocks were used to examine the effects of different levels (one to three generations) of domestication on the genetic characteristics of hatchery populations. Allelic richness at seven microsatellite loci in all hatchery populations was lower than that in a wild population. Genetic variation measured by allelic richness and heterozygosity tended to decrease with an increase in generations of domestication. In addition, the degree of genetic differentiation from a wild population increased with an increase in generations of domestication. Significant differences in three morphometric traits (dorsal and anal fin ray counts and vertebral counts) and three physiological traits (high temperature, salinity and formalin tolerance) were observed among the hatchery populations. The degree of phenotypic difference among populations was larger in morphometric traits than in physiological traits. The divergence pattern of some quantitative traits was similar to that observed at microsatellite loci, suggesting that domestication causes the decrease of genetic variation and the increase of genetic differentiation for some quantitative traits concomitantly with those for microsatellite loci. Significant positive correlation was observed between F _ST and the degree of phenotypic difference in the three morphometric traits and formalin tolerance, indicating that genetic variation at microsatellite loci predicts the degree of phenotypic divergence in some quantitative traits.     

Interactions between natural and farmed fish populations: information from genetic markers

Studies on genetic changes in farmed fish populations are reviewed, and the potential interactions between wild and farm escapee, and between wild and stocked, fish populations are discussed. Examples of the application of genetic markers in studies concerning survival and reproduction of stocked fish, and genetic and ecological interactions between stocks, are given for brook trout, Salvelinus fontinalis , brown trout, Salmo trutta , rainbow trout, Salmo gairdneri , cod, Gadus morhua , Guadalupe bass, Micropterus treculi , walleye, Stizostedion vitreum vitreum and chum salmon, Oncorhynchus keta . The various studies produced different results. Evidence for successful reproduction and genetic interactions between released and wild stocks have been found in a few cases. Stocked genetic material sometimes had a lower reproductive success than wild material. In one case the transplanted genetic material failed to acclimatize, and was apparently lost from the genepool in two generations. Investigations on the genetic and ecological interactions between wild and farmed populations are of great importance to the preservation of wild populations and their genetic resources.     

Loss of genetic diversity in farmed populations of Colossoma macropomum estimated by microsatellites

The genetic variability of four Colossoma macropomum broodstocks, three from fish farms in different regions and one from the natural environment in Brazil, was analyzed using microsatellite markers. The wild progeny (n = 30) were caught in the Solimões–Amazonas River, at the varzea lakes; this location is used to mature the fish from larvae to juveniles. The three fish farms were selected according to the age of their lineages and broodstock availability: DNOCS (n = 21) is located in the Ceará State, representing the oldest lineage of cultivated tambaqui in Brazil; Balbina (n = 30) is located in the Amazonas State, representing the youngest stocks of tambaqui farmed in Brazil (approximately 15 years); and UFRPE (n = 30) is located in the Pernambuco State and is considered to be a mixed stock formed from the DNOCS and Balbina lineages. The analysis of 13 microsatellite loci indicated the occurrence of a variability reduction in the farmed populations; the UFRPE stock was the population with the highest diversity level. Low values of molecular coancestry were found in these populations. Additionally, significant differences in the R_ST values among the populations were detected, as was the occurrence of genetic structure. The genetic loss found in these populations may have been influenced by the founder effect. Because no breeding programs were during the entire production period and no pedigree records were kept for these broodstocks, we suggest that a wild population might be used as an important genetic resource to increase the genetic diversity of renewal stock lineages.     

A single origin and moderate bottleneck during domestication of soybean (Glycine max): implications from microsatellites and nucleotide sequences

Background and Aims

It is essential to illuminate the evolutionary history of crop domestication in order to understand further the origin and development of modern cultivation and agronomy; however, despite being one of the most important crops, the domestication origin and bottleneck of soybean (Glycine max) are poorly understood. In the present study, microsatellites and nucleotide sequences were employed to elucidate the domestication genetics of soybean.

Methods

The genomes of 79 landrace soybeans (endemic cultivated soybeans) and 231 wild soybeans (G. soja) that represented the species-wide distribution of wild soybean in East Asia were scanned with 56 microsatellites to identify the genetic structure and domestication origin of soybean. To understand better the domestication bottleneck, four nucleotide sequences were selected to simulate the domestication bottleneck.

Key Results

Model-based analysis revealed that most of the landrace genotypes were assigned to the inferred wild soybean cluster of south China, South Korea and Japan. Phylogeny for wild and landrace soybeans showed that all landrace soybeans formed a single cluster supporting a monophyletic origin of all the cultivars. The populations of the nearest branches which were basal to the cultivar lineage were wild soybeans from south China. The coalescent simulation detected a bottleneck severity of K′ = 2 during soybean domestication, which could be explained by a foundation population of 6000 individuals if domestication duration lasted 3000 years.

Conclusions

As a result of integrating geographic distribution with microsatellite genotype assignment and phylogeny between landrace and wild soybeans, a single origin of soybean in south China is proposed. The coalescent simulation revealed a moderate genetic bottleneck with an effective wild soybean population used for domestication estimated to be ≈2 % of the total number of ancestral wild soybeans. Wild soybeans in Asia, especially in south China contain tremendous genetic resources for cultivar improvement.     

Genetic differentiation between collections of hatchery and wild masu salmon (<Emphasis Type="Italic">Oncorhynchus masou</Emphasis>) inferred from mitochondrial and microsatellite DNA analyses

There has been very little effort to understand genetic divergence between wild and hatchery populations of masu salmon (Oncorhynchus masou). In this study, we used mitochondrial (mt) NADH dehydrogenase subunit 5 gene (ND5) and six polymorphic nuclear microsatellite DNA loci to compare the genetic variability in three hatchery broodstocks of masu salmon with the variability in eight putative wild masu populations sampled in five rivers including one known source river for the hatchery broodstocks. Both ND5 and microsatellites showed no significant genetic divergence (based on F_ST estimates) between four annual collections from the source river population, suggesting no change in genetic diversity over this time period. The F_ST estimates, an analysis of molecular variance (AMOVA), and a neighbor-joining tree using both DNA markers suggested significant differentiation between the three hatchery and all eight putative wild populations. We conclude that genetic diversity of hatchery populations are low relative to putative wild populations of masu salmon, and we discuss the implications for conservation and fisheries management in Hokkaido.     

Failure of a stocking policy, of hatchery reared brown trout, Salmo trutta L., in Asturias, Spain, detected using LDH-5* as a genetic marker

A useful genetic marker exists through the apparent fixation of the LDH-5 * 100 allele in wild populations of brown trout in rivers from Asturias, Spain, contrasted with the near fixation of the LDH-5 * 90 allele in hatchery populations used to stock these rivers. In sampling locations where natural reproduction occurred, the * 100 allele was found exclusively in all areas having no record of hatchery stocking. The * 100 allele also predominated in three stocked areas having natural reproduction; in two of these areas a few individuals of the 0 + age class were homozygous for the * 90 allele. These data indicated that all catchable and reproductive fish originated from indigenous populations and thus the policy of hatchery supplementation was a failure in these areas.     

Gene diversity analysis in natural populations and cultured stocks of turbot (Scophthalmus maximus L.)

The genetic variability of eight fish-farm and three natural populations of turbot was studied by electrophoretic analysis of 35 enzymatic loci. The results showed low genetic variability in natural populations of turbot ( H _T = 0·029 ± 0·013) in comparison with other flatfish species. Great genetic similarity was revealed among the natural populations studied, which indicates high rates of gene flow in this species. The hatchery stocks showed less genetic variation than the wild populations analysed, which suggests genetic drift phenomena involved in the foundation and management of broodstocks. In addition, the heterozygosity differences detected among the hatchery stocks analysed are correlated with inverted levels of fluctuating asymmetry, which supports the existence of inbreeding depression phenomena in turbot culture.     

Levels and Patterns of Genetic Diversity and Population Structure in Domestic Rabbits

Over thousands of years humans changed the genetic and phenotypic composition of several organisms and in the process transformed wild species into domesticated forms. From this close association, domestic animals emerged as important models in biomedical and fundamental research, in addition to their intrinsic economical and cultural value. The domestic rabbit is no exception but few studies have investigated the impact of domestication on its genetic variability. In order to study patterns of genetic structure in domestic rabbits and to quantify the genetic diversity lost with the domestication process, we genotyped 45 microsatellites for 471 individuals belonging to 16 breeds and 13 wild localities. We found that both the initial domestication and the subsequent process of breed formation, when averaged across breeds, culminated in losses of ~20% of genetic diversity present in the ancestral wild population and domestic rabbits as a whole, respectively. Despite the short time elapsed since breed diversification we uncovered a well-defined structure in domestic rabbits where the F_ST between breeds was 22%. However, we failed to detect deeper levels of structure, probably consequence of a recent and single geographic origin of domestication together with a non-bifurcating process of breed formation, which were often derived from crosses between two or more breeds. Finally, we found evidence for intrabreed stratification that is associated with demographic and selective causes such as formation of strains, colour morphs within the same breed, or country/breeder of origin. These additional layers of population structure within breeds should be taken into account in future mapping studies.     

Genetic diversity of wild grapevine populations in Spain and their genetic relationships with cultivated grapevines

The wild grapevine, Vitis vinifera L. ssp. sylvestris (Gmelin) Hegi, considered as the ancestor of the cultivated grapevine, is native from Eurasia. In Spain, natural populations of V. vinifera ssp. sylvestris can still be found along river banks. In this work, we have performed a wide search of wild grapevine populations in Spain and characterized the amount and distribution of their genetic diversity using 25 nuclear SSR loci. We have also analysed the possible coexistence in the natural habitat of wild grapevines with naturalized grapevine cultivars and rootstocks. In this way, phenotypic and genetic analyses identified 19% of the collected samples as derived from cultivated genotypes, being either naturalized cultivars or hybrid genotypes derived from spontaneous crosses between wild and cultivated grapevines. The genetic diversity of wild grapevine populations was similar than that observed in the cultivated group. The molecular analysis showed that cultivated germplasm and wild germplasm are genetically divergent with low level of introgression. Using a model‐based approach implemented in the software structure , we identified four genetic groups, with two of them fundamentally represented among cultivated genotypes and two among wild accessions. The analyses of genetic relationships between wild and cultivated grapevines could suggest a genetic contribution of wild accessions from Spain to current Western cultivars.     

Genetic diversity and relationships of wild and cultivated olives in Turkey

In the present study, we proposed to determine the genetic diversity and relationships between local cultivars and wild olive trees from three important olive-growing regions, i.e., Marmara, Aegean, and Mediterranean, of Turkey. This is the first known large-scale molecular study to investigate the relationships between local cultivars and wild olives from the eastern Mediterranean basin. Two hundred and four oleaster trees and 27 cultivars were sampled to represent molecular diversity. We used 11 simple sequence repeat and 13 sequence-related amplified polymorphism markers to assess genetic variations and inter-relationships among the samples. The results of the analysis showed differences in the levels of allelic composition and heterozygosity between cultivated and wild olive trees. The observation of a high proportion of a certain wild-type genetic background in the cultivars may indicate the former use of local wild trees in olive domestication in Turkey, a possible autochthonal origin of cultivars. “Gemlik” was found to be the most common olive cultivar in the Marmara region and most of the wild olive samples from this region may be feral forms derived from cultivar seed spreading. The information obtained from this study can help to assist the management of an olive collection and sheds some light on the origin of Turkish olive cultivars.     

Genetic variation within and among domesticated Atlantic salmon broodstocks in British Columbia, Canada

Atlantic salmon have been reared in the British Columbia, Canada aquaculture industry since the early 1980s. No breeding programmes spanned the entire production period and pedigree records were not kept for broodstocks prior to or since importation. Of the three recognized industry strains, two are of European ancestry ('Mowi' from Norway and 'McConnell' from Scotland) and one is of North American heritage ('Cascade' from Gaspe, Quebec). We evaluated the amount and distribution of genetic variation within industry broodstocks by surveying microsatellite variation at 11 loci in 20 broodstock groups sampled from major production facilities. Allelic richness averaged 10.9 (range 5.8-13.8), compared with a value of 20.3 obtained for a North American wild population. Pairwise genetic distances (D(S)) between samples within strains were generally less than those between strains, with samples attributed to the same strain clustering together in a neighbour-joining dendrogram. Nevertheless, average distances between samples within the European strains were high (0.41 for Mowi; 0.71 for McConnell) but lower (0.06) for the Cascade strain. The reduced intra-sample and increased intra-strain genetic variation observed for the BC domesticated samples compared with wild populations was similar to observations for European domesticated Atlantic salmon. Evidence of introgression of the Cascade strain into European broodstocks was provided by the presence of large Ssa202 alleles (confined to North America in wild populations) in some Mowi and McConnell samples. Introgression likely also contributed to the decreased intercontinental genetic distance for the domesticated samples of this study compared with that observed for wild populations.     

三疣梭子蟹增养殖过程对野生种群的遗传影响——以海州湾为例

为探明三疣梭子蟹人工增殖与养殖活动对野生资源的遗传影响,本文利用20对SSR引物对海州湾三疣梭子蟹野生群体与两个养殖群体进行群体遗传结构和遗传分化研究。结果表明,野生种群遗传多样性明显高于养殖群体,其群体杂合度Ho为0.8509,而两个养殖群体的杂合度Ho分别为0.4525和0.5283。海州湾野生三疣梭子蟹的 Ne、Ho、He、PIC均显著高于两个养殖群体（P<0.05）但两养殖群体的 Ne、Ho、He、PIC均无显著差异（P>0.05）。以上结果说明海州湾天然三疣梭子蟹群体的遗传多样性显著高于养殖群体。三群体间遗传分化处于中度水平（Fst,0.1085~0.1448）,基因流Nm处于1.5-2.0间,野生群体与养殖群体的遗传分化比养殖群体内部之间大,基因流也较养殖群体内部之间要小,表明野生群体与养殖群体存在一定的分化,基因流处于中等程度。因此,当前海州湾天然三疣梭子蟹遗传状况良好,养殖活动和人工增殖放流对天然资源的遗传影响还很有限,这可能与海州湾人工养殖三疣梭子蟹时间较短、人工放流的规模较小、时间较短有关。     

Genetic mapping of a new race specific resistance allele effective to Puccinia hordei at the Rph9/Rph12locus on chromosome 5HL in barley

Background

Tea is one of the most popular beverages in the world. Many species in the Thea section of the Camellia genus can be processed for drinking and have been domesticated. However, few investigations have focused on the genetic consequence of domestication and geographic origin of landraces on tea plants using credible wild and planted populations of a single species. Here, C. taliensis provides us with a unique opportunity to explore these issues.

Results

Fourteen nuclear microsatellite loci were employed to determine the genetic diversity and domestication origin of C. taliensis, which were represented by 587 individuals from 25 wild, planted and recently domesticated populations. C. taliensis showed a moderate high level of overall genetic diversity. The greater reduction of genetic diversity and stronger genetic drift were detected in the wild group than in the recently domesticated group, indicating the loss of genetic diversity of wild populations due to overexploitation and habitat fragmentation. Instead of the endangered wild trees, recently domesticated individuals were used to compare with the planted trees for detecting the genetic consequence of domestication. A little and non-significant reduction in genetic diversity was found during domestication. The long life cycle, selection for leaf traits and gene flow between populations will delay the emergence of bottleneck in planted trees. Both phylogenetic and assignment analyses suggested that planted trees may have been domesticated from the adjacent central forest of western Yunnan and dispersed artificially to distant places.

Conclusions

This study contributes to the knowledge about levels and distribution of genetic diversity of C. taliensis and provides new insights into genetic consequence of domestication and geographic origin of planted trees of this species. As an endemic tea source plant, wild, planted and recently domesticated C. taliensis trees should all be protected for their unique genetic characteristics, which are valuable for tea breeding.     

Genetic risk of domestication in artificial fish stocking and its possible reduction

Genetic hazards associated with the stocking of fish juveniles produced in hatcheries were studied with simple mathematical models. Domestication is the process of acquiring a genetic characteristics that are advantageous in a hatchery environment but that are disadvantageous in a natural environment due to the selection pressure in the hatchery differing from that in the natural environment. Conditions for the propagation of mutants enhancing domestication were obtained for a variety of stocking strategies specified by parameters related to hatchery productivity and kind of brood stock used. By using this, the possibility of reducing the risk of domestication was studied. As a means of reducing the risk, selective use of wild-born individuals for brood stock was considered. The effectiveness of this was analyzed for both the cases where all brood stock is collected from the wild, and the male brood stock is collected from the wild and the female brood stock is born and reared in a hatchery. We also estimate how much hatchery release can be increased without increasing the risk by employing these means. It is concluded that the use of only male brood stock from the wild is not very effective in reducing the risk of domestication. Further, it is concluded that selective use of the wild-born individuals of both sexes for brood stock is highly desirable if the contribution of released individuals to the natural reproduction is high. In other words, substantial increase of hatchery release may be possible while keeping risk at a level comparable to that under moderate hatchery release, if it is accompanied by the selective use of wild-born individuals for brood stock.