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The Pacific oyster (Crassostrea gigas) is a widely cultured shellfish species with great economic value; however, estimation of heritabilities for meat composition traits meat composition have not been studied with molecular pedigree. In this study, the heritabilities of six meat composition traits were studied using near-infrared reflectance spectroscopy (NIRS) in the golden shell strain of Pacific oyster. All 30 families used in this study were produced by nested mating. In total, progeny from crosses among 10 sires and 30 dams were communally reared and pedigree was reconstructed with six microsatellite markers. A total of 608 offspring were harvested at 16 months of age and unambiguously assigned to their respective parents. We estimated the heritability at 0.41 ± 0.19 for glycogen content, 0.51 ± 0.09 for total protein content, 0.89 ± 0.18 for total fat content, 0.40 ± 0.11 for zinc content, 0.87 ± 0.06 for selenium content and 0.65 ± 0.13 for ash content. Remarkably, there were moderate negative genetic correlations between protein and both glycogen (−0.65 ± 0.11) and fat content (−0.40 ± 0.09) as well as between shell height and glycogen content (−0.68 ± 0.11). Overall, this study demonstrated that in meat composition traits could be improved through selective breeding under commercial conditions. The correlations among composition traits and growth traits should be taken into consideration. • Genetic parameters for meat composition traits in the golden shell color strain of C. gigas was estimated. • The meat composition traits were determined with near-infrared reflectance spectroscopy (NIRS) technology. • The families of oysters were fostered communally and reconstructed with six microsatellite makers. [ABSTRACT FROM AUTHOR]

Abstract The Pacific oyster (Crassostrea gigas) is one of the highly fecund marine aquaculture species and has a large variance in reproductive success, these characteristics can result in loss of genetic diversity and inbreeding especially when conducting mass selection. In the current study, we investigated the level of genetic diversity and effective population size over three successive mass-selected generations in the black shell strain of C. gigas assessed by 11 microsatellites as well as mitochondrial COI region. The results showed that the genetic variation over three generations were maintained since no detectable depression of expected heterozygosity (H e = 0.647–0.681), number of alleles (N = 5.6–6.0) and haplotypes (N h = 2). The difference in alleles and haplotypes number between the base population (BP) and three mass selective generations (M5-M7) could be mainly due to the loss during preceding family selection process. Pair-wise F ST values along with AMOVA analysis from both markers indicated unremarkable differentiation within each generation including BP. There was no deleterious effect on genetic diversity and population structure for mass selected generations imposed by our artificial breeding practice. The N eb estimation for M5, M6 and M7 was 29.8, 40.7 and 52.7, respectively. The different number of broodstocks used for each generation implied that using a balanced sex ratio and large size of broodstock as well as low selection pressure would help to increase the effective population size and avoid high level of inbreeding. The estimated linkage disequilibrium-based effective breeders size (N eb) was significantly lower than sex-ratio correction effective population size (N e), which indicated high variance in family contribution. It is suggested during mass spawning to simply undertake several mini-spawn groups and then pool the embryos to produce next generation, which can be a hedge to the high variance in reproductive success, thus, the loss of effective populations size and diversity. Other practical strategies against the loss of genetic diversity were also discussed, however, it remains to be investigated how diverse selection and follow-up procedures will benefit retaining genetic variability. This study will provide an insight into the level of genetic diversity and effective population size within mass-selected black shell line and enable a better understanding of how efficient current breeding practices are at maintaining genetic variation. This information can be applied for future selective breeding program and in the design of suitable management guidelines for sustainable breeding of C. gigas. Highlights • Genetic diversity and effective population size over successive mass-selected generations in the black shell strain were assessed. • There was no detectable loss of genetic diversity revealed by 11 microsatellites and mtDNA COI region. • A large size and balanced sex-ration of broodstock and lower selection pressure would alleviate effective population size loss. • It is suggested to simply undertake mini-spawning during mass spawning to against high variance in reproductive success. [ABSTRACT FROM AUTHOR]

The pacific oyster ( Crassostrea gigas ) is one of the most widely farmed aquatic animal species and of great economic importance. Mantle edge color in C . gigas is highly variable and considered as a new potential trait for a better commercial value. In this study, heritability for mantle edge pigmentation and its correlation with shell pigmentation were explored in the white-shell strain of C . gigas with mixed-family method. A total of 460 offspring raised under communal conditions were successfully assigned to their parents using four multiplex PCR protocols based on 11 microsatellite loci. Mantle edge pigmentation was measured through assay of melanin content using spectrophotometric analysis. Animal model heritability estimate were 0.215 ± 0.092 for mantle edge pigmentation. The genetic and phenotypic correlations between two pigment traits were 0.980 ± 0.094 and 0.423 ± 0.042, respectively. Pearson analyses for average mantle edge and shell pigmentation of family also showed strong and significant correlation ( r = 0.729, P = 0.000, n = 29). Chi-square analyses showed that mantle edge pigmentation of family 7 segregated into “lighter” and “darker” groups in a 3:1 ratio ( P = 0.833), suggesting that a major locus might control mantle edge pigment trait. The results obtained in this study will benefit selective breeding of C . gigas with desired mantle and shell pigmentation. [ABSTRACT FROM AUTHOR]

The Pacific oyster ( Crassostrea gigas ) is an important aquatic animal species with enormous production and economic benefits, but heritability estimation for shell color applying mixed-family approach and computer vision system has not been performed. In this study, heritability for shell color-related traits was estimated in the golden shell strain of Pacific oyster by fostering a single cohort of 30 families in a nested mating design consisting of 10 sires and 30 dams. After parentage assignment inference based on six microsatellite markers, 690 offspring were included in the subsequent analyses. Using an animal model, at 16 months of age, heritability estimates were 0.10 ± 0.12 for L ⁎ , 0.41 ± 0.16 for a ⁎ , 0.23 ± 0.15 for b ⁎ and 0.33 ± 0.19 for Δ E . Genetic correlation between shell color-related traits and growth-related traits were generally inconspicuous ranging from − 0.02 to 0.11. Conclusions can be obtained from our study that favourable improvement in aquatic selective breeding would be predictable for the genetic potential of the golden shell color in this strain of Pacific oyster, whereas independent selection conducted at the same time rather than correlative selection would be feasible in the improvement of both types of traits. [ABSTRACT FROM AUTHOR]

Crassostrea nippona has recently been identified as a potential aquaculture species for its high glycogen content and delicate flavor in summer when Crassostrea gigas suffer from low meat quality. In 2014, we initiated the selective breeding program to improve growth traits of C. nippona through successive generations of mass selection, yet the genetic impact of an intense artificial selection on the genetic variability of C. nippona was not fully understood. In this study, the genetic diversity and genetic structure of three generations of mass-selected lines (G1-G3) and three wild populations were investigated using both 15 microsatellite loci and mitochondrial COI sequences (mtCOI). The selected lines exhibited no significant decrease in the average number of alleles (N a : 7.53–9.87), observed heterozygosity (H o : 0.58–0.64), expected heterozygosity (H e : 0.67–0.71) and alleles richness (A r : 6.35–7.75), compared with those of the wild populations. The abundant genetic diversity of selected lines was successfully maintained during three generations of mass selection due to no detectable loss. The effective population sizes (N e − lin) estimated by linkage disequilibrium methods for G1, G2 and G3 were 64.1, 25.3 and 47.4, respectively. Moreover, little genetic differentiation within the selected lines was observed in AMOVA analysis (global F ST : 0.005, P > 0.05) and significant genetic differentiation among the wild populations was revealed by global F ST (0.15, P < 0.01), pairwise F ST (0.095–0.211), Nei's D (0.260–0.730) and clustering results, which might suggest genetically isolated populations occurring in these sampling locations. To maximize future selective breeding efforts, a larger scale of broodstock and multi-line breeding strategy along with alleviating selection intensity is recommended against the reduction in the genetic diversity and effective population size in subsequent breeding practices. This study contributes to an increasing understanding of the efficiency of current breeding procedures in maintaining genetic variation and provides insight into future genetic improvement programs of C. nippona. • This study is the first to investigate the genetic diversity of C. nippona using both microsatellites and mtCOI. • Microsatellite analysis revealed no significant difference in genetic diversity between selected and wild populations. • The genetic diversity of the selected lines was successfully maintained over successive generations of mass selection. • Little genetic differentiation among the selected lines was observed based on the microsatellite result. [ABSTRACT FROM AUTHOR]