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Triploid Crassostrea angulata has the advantages of fast growth, poor fertility and high quality. However, due to poor fertility, direct genetic improvement is difficult. Mating between tetraploid males and diploid females has been shown to be the best method for commercial triploid production, so genetic improvement of tetraploids will directly affect the phenotypic traits of triploid offspring. However, to date, few studies have investigated the genetic improvement of tetraploid oysters. Based on the induced tetraploid C. angulata population, this study carried out three successive generations of growth selective breeding research, and systematically compared the growth, survival, ploidy composition and sex ratio of the selected group and the control group. The results showed that there was no significant difference in the survival rate from planktonic larvae to adult between the two groups. However, the growth of the selected group was significantly higher than that of the control group, that was, the shell height and whole weight of S3 were significantly higher than that of C3, and the selection advantage of shell height increased from 7.80% of S1 to 34.68% of S3. The ploidy composition of the two tetraploid groups was relatively stable before the 90th days, but on the 270th day, some tetraploids underwent chromosome loss and transformed into diploids or triploids, which might be related to gametogenesis of tetraploids. Moreover, with the increase of generations, the number of individuals with chromosome loss in the selected group gradually decreased, and their ploidy became more stable than that in the control group. In addition, both groups were fertile, with a sex ratio of more males than females, and a proportion of hermaphrodite individuals. In conclusion, this study successfully selected a fast growth line of tetraploid C. angulata , which can be used for commercial production of fast-growing triploid C. angulata , and provides a basis and reference for the genetic improvement of tetraploid oysters. • Firstly carried out the genetic improvement of tetraploid C. angulata by selective breeding. • The growth traits of selected groups were significantly improved than those of control group. • Both groups underwent ploidy conversion, but the selected group had a relatively more stable ploidy. • The selected tetraploids were fully fertile and present many males and hermaphrodite individuals. • This study provided excellent parental sources for commercial production of fast growth triploids. [ABSTRACT FROM AUTHOR]

Triploids have received increasing attention in the industrialization of oysters due to their fast growth rate, tolerance, and their sterility to be marketed year-round. Cultivating varieties or lines with special colors could be crucial for germplasm enrichment as well as traceability and intellectual property protection during the commercialization process. However, triploids and tetraploids with special colors have not been studied in the Fujian oyster Crassostrea angulata , which has seriously limited their commercialization and scalability. In this study, diploid and tetraploid C. angulata with normal, golden and black shell colors were used as parents and their corresponding triploids were constructed. The growth and survival of the nine groups were comprehensively evaluated during the larval and grow-out stages. Sex ratio, ploidy composition and thermotolerance were also statistically compared. All three triploid groups (NDT, GDT and BDT) exhibited significant advantages in growth and survival, compared to their diploid (NDD, GDD and BDD) and tetraploid (NTT, GTT and BTT) counterparts in all three sites. The triploid advantages in survival rate among NDT, GDT and BDT were 38.36%, 40.38% and 36.00%, respectively, at Jiaonan at day 480. Moreover, higher thermotolerances were exhibited in NDT, BDT and GDT, with the values of LT 50 at 41.77 °C, 42.28 °C and 42.13 °C, respectively. On the contrary, the three tetraploid C. angulata lines (NTT, GTT and BTT) exhibited poor growth, survival and thermotolerances. The values of LT 50 for GTT and NTT were comparable and lower than this of BTT (GTT: 39.85 °C; BTT: 41.05 °C; NTT: 39.57 °C). It is encouraging to note that the tetraploid rates also remained above 80% at day 480 in all three tetraploid lines. Based on our study, the three triploid C. angulata lines with normal, black, and golden shell colors showed great potential and can be industrialized as new varieties to improve the oyster industry. However, the inferior performance of tetraploids should not be overlooked and demands extra concern in the future breeding process. • We firstly constructed diploid, triploid and tetraploid Crassostrea angulata with normal, golden and black shell colors. • Significant triploid advantages in survival, growth and thermotolerance were observed among all three triploid lines. • The tetraploid rates also remained above 80% at day 480 in all three tetraploid lines. • The significant advantages of triploids and the inferior performance of tetraploids cannot be overlooked in the breeding process. [ABSTRACT FROM AUTHOR]

The application of cold shock to inhibit the extrusion of the second polar body in fertilized eggs is one of the main methods to induce triploid in diploid fish. In this study, we originally planned to induce hexaploid by this method in tetraploid carp. However, among the surviving offspring, we observed only 50.7% tetraploid and 49.3% diploid individuals, which could potentially result from either androgenetic diploids or gynogenetic diploids. The absence of irradiation and the high proportion of diploids attracted us. However, the lack of sex-specific markers for tetraploid carp, makes it difficult to determine their origin. Fortunately, we also carried out the cross of yellow carp (Cyprinus carpio yellow var., 2n, ♀) × tetraploid carp (♂) and red crucian carp (Carassius auratus red var., 2n, ♀) × tetraploid carp (♂) with cold shock inhibiting the second meiosis, diploid offspring have also been found, and whether they have undergone gynogenesis or androgenesis can be judged based on phenotype and genotype. In terms of phenotypes, the key phenotypes of two diploids, such as the whisker length, number of lateral scales, and presence of melanin, are consistent with tetraploid carp. In terms of genotypes, through single-copy nuclear gene cloning and fluorescence in situ hybridization (FISH), it is supported that both diploids are androgenetic offspring. In addition, 14.9% of tetraploid offspring were found in red crucian carp (♀) × tetraploid carp (♂) with cold shock inhibiting the second meiosis. By the above-mentioned means of detection, it was found that they were created by inhibiting the extrusion of the second polar body of the fertilized eggs. From this it will be seen that the application of cold shock before the extrusion of the second polar body of fertilized eggs cause not only polyploidy, but also the elimination of both second polar body and female nucleus. Previous studies have found that cold shock can induce lethal androgenetic haploids in diploid fish, but these androgenetic diploid fish produced by tetraploid carp sperm were surviving. We summarize the mechanism behind the above phenomenon, which is mainly related to meiosis occurring at the edge of the cell membrane. Cold shock may disrupt the function of the spindle, resulting in the simultaneous retention or extrusion of female nucleus and second polar body. This study will provide valuable insights into androgenesis, polyploidization, and hybridization in fish genetic breeding. • Androgenetic diploids were induced from tetraploid carp sperm by cold shock without irradiating the eggs. • New-type allotetraploids were induced in the cross between male tetraploid carp and female diploid carp by cold shock. • Nuclear gene cloning is suitable for qualitative analysis of the genetic composition of hybrids, but not for quantitative analysis. [ABSTRACT FROM AUTHOR]

Tetraploid oysters hold a significant position in the global oyster industry, particularly as core germplasm resources for the production of triploids. Triploids exhibit desirable characteristics such as reduced gonadal development, larger adult size, and superior flesh quality compared with diploids. However, tetraploids often face challenges of slow growth and chromosomal instability during the breeding process, and the mechanisms underlying the formation of these polyploid characteristics remain unclear. This study aimed to elucidate these mechanisms by constructing a polyploid oyster system and comparing the differences in growth-related phenotypes and gene expression among diploids, triploids, and tetraploids. We identified 1404 differentially expressed genes (DEGs) between diploids and triploids, 1814 DEGs between triploids and tetraploids, and 933 DEGs between diploids and tetraploids. Furthermore, we observed distinct gene expression patterns related to innate immunity response and biomineralization between different ploidy levels. Through trend analysis, we clustered genes with similar expression level changes across different ploidy levels and conducted gene ontology (GO) enrichment analysis on genes with different expression profiles. The results indicated that genes associated with the innate immunity response exhibited significantly upregulated expression with increasing ploidy, while genes related to biomineralization showed higher or lower expression levels in triploid oysters. As biomineralization is closely linked to oyster shell growth, this highlights the crucial role of genes associated with biomineralization in regulating the rapid shell growth observed in triploid oysters. Confronted with environmental challenges, tetraploid oysters may display a stronger innate immune response than diploids and triploids. Our study provides valuable resources for investigating the functional aspects of genes related to polyploid phenotype differences and offers new insights into the molecular mechanisms of existing issues in tetraploid oyster breeding. • Triploid oysters show enhanced calcium transport, regulation, and protein degradation. • Chromosomal duplication affects polyploid oysters' growth and adaptability. • Gene replication exhibits detrimental dosage effects following duplication. [ABSTRACT FROM AUTHOR]

Polyploid fish have valuable applications in aquaculture, and artificial breeding of polyploids is an important field of aquatic research. In this study, fertilized eggs (65–100 min post-fertilization (mpf)) were treated with 650–750 kg/cm2 hydrostatic pressure for 3–6 min to induce tetraploidy. The optimal rates for hatching and tetraploidization of embryos were achieved at 4.70% and 23.33%, correspondingly. Flow cytometry analysis revealed that the DNA content of tetraploidized embryo cells was approximately twice that of the wild-type. The chromosome number of the tetraploidized rice field eels was 48. In this study, artificially induced tetraploid rice field eels were able to survive, with four of them reaching 20 months of age. Measurement of erythrocyte nuclei revealed that the nuclear area of erythrocytes from tetraploids increased and was approximately twice that of the diploids. Histological analysis showed that the gonads of tetraploids developed into testes, and spermatogenetic germ cells were observed. In conclusion, a technique to induce tetraploidization has been developed for rice field eels by applying 700 or 750 kg/cm2 hydrostatic pressure on 85 mpf embryos for 5 min. The viable tetraploidized rice field eels were produced using this approach. • A method for hydrostatic pressure shock-induced tetraploid rice field eel was established. • Artificially induced tetraploid rice field eels survived and grow up to adult. • The gonad of tetraploid rice field eel developed into testis and may be fertile. [ABSTRACT FROM AUTHOR]

Distant hybridization occurs widely in fishes and is a useful strategy to produce different ploidy offsprings. In this study, we obtained androgenetic blunt snout bream (2n = 48, ADBSB), triploid hybrids (3n = 124, 3nJB) and tetraploid hybrids (4n = 148, 4nJB) from the hybridization of two species from different subfamilies: Carassius cuvieri (♀, 2n = 100, JCC) and Megalobrama amblycephala (♂, 2n = 48, BSB). The ploidy levels of ADBSB, 3nJB and 4nJB hybrids were confirmed by counting chromosomal numbers, forming chromosomal karyotype, and measuring DNA content. In the phenotypes and reproductive traits, 3nJB and 4nJB exhibited significantly divergences from JCC and BSB, but ADBSB took after BSB. Fluorescence in situ hybridization (FISH) and 5S rDNA analyses revealed that the genetic traits of the offsprings compared with those of their parents. This is the first report on the coexistence in vertebrates of viable androgenetic, triploid and tetraploid hybrids being produced by crossing JCC and BSB. The formation of the different ploidy offspring is great significance in both evolution and fish genetic breeding and it also provides a good model for studying the genomic variation in the first generation of interspecific hybrids. [ABSTRACT FROM AUTHOR]

Selection and polyploidization are two practical tools for improving productive traits of oysters. To evaluate the aquaculture traits of diploids, triploids and tetraploids of 'Haida No. 3' line of the Pacific oyster Crassostrea gigas , four mating combinations (HD- diploid 'Haida No. 3' line ♀ × diploid 'Haida No. 3' line ♂, HTR- diploid 'Haida No. 3' line ♀ × tetraploid 'Haida No. 3' line ♂, HTE- tetraploid 'Haida No. 3' line ♀ × tetraploid of 'Haida No. 3' line ♂, WD- wild diploid ♀ × wild diploid ♂) were established. At both Rongcheng and Rushan sites, HD had a larger shell height and wet weight than WD. HTR outperformed HD in growth and survival, with a consistently positive value of triploid advantage (TA). On the day 480 at Rushan site, the triploid advantages in terms of shell height, wet weight and cumulative survival were 20.70%, 40.28% and 29.27%, respectively. HTE were the lowest in growth and survival compared to the other three groups. Histomorphometric analysis revealed that HTR were partial highly sterile, indicating its gonadal atrophy and gamete abnormalities. In contrast, HD and HTE were fully fertile and contained functional gametes. During the whole culture period, HTR remained 100% triploid rate while HTE maintained a tetraploid rate of over 80%. HTR and HTE exhibited rapid growth and stable black shell color, suggesting that these traits were stably inherited by the ploidy change. Overall, our results demonstrated that polyploidization based on selective line had favorable performance for aquaculture, which would have vital practical interest for oyster culture in northern China. • The aquaculture performances of diploids (HD), triploids (HTR), tetraploids (HTE) of 'Haida No. 3' line were evaluated. • HTR presented triploid advantages in growth and survival, and were partially sterile. • HTE had the lowest growth and survival, exceeding 80% of tetraploid rate. • HTR and HTE exhibited rapid growth and black shell color as HD. [ABSTRACT FROM AUTHOR]

Triploid is widely cultivated in China and many other oyster-producing countries for the advantages of fast growth, favorable infertility and better meat quality. However, triploid Crassostrea gigas is found to have disadvantages of slow growth in later grow-out stage and high summer mortality, while the triploid C. angulata has the disadvantages of fragile shells and a relatively high ratio of developed gonads in population, and therefore, both of them have space for further improvement. Due to the limitations of poor fertility and low survival of offspring, triploid genetic improvement cannot be carried out directly. Hybridization between species is a useful method for indirect genetic improvement of triploids, and natural crosses between tetraploid males and diploid females have proven to be the best method for commercial promotion of triploids. The growth, survival and gonad development of autotriploids (DGTG-diploid C. gigas ♀ × tetraploid C. gigas ♂, DATA-diploid C. angulata ♀ × tetraploid C. angulata ♂) and allotriploids (DATG-diploid C. angulata ♀ × tetraploid C. gigas ♂, DGTA-diploid C. gigas ♀ × tetraploid C. angulata ♂) were investigated in this study. It is showed that the fertilization rates of autotriploids were significantly higher than that of allotriploids, and DATG larvae grew significantly faster than the other three groups (P < 0.05). DGTA had significant shell height, whole weight and survival advantages at Laizhou site (P < 0.05), while DATG exhibited significantly fastest growth and highest survival at Zhangpu site (P < 0.05), but both DATG and DATA showed significantly faster growth and higher survival at Beihai site (P < 0.05), with no significant difference between them (P > 0.05). Sites, genotypes and their interaction always presented significant effects on shell height and whole weight from the 90th to 360th day, but not on survival with the 180th day as an exception. Gonad examination confirmed that the proportions of fertile individuals in the groups with maternal C. gigas (DGTG and DGTA) were lower than that in the groups with maternal C. angulata (DATA and DATG), and DATA always had the highest rate of developed gonad at three sites. These results indicate that DGTA has advantages in growth, survival and infertility in northern China while DATG performs best in southern China, which exhibits that there is a significant maternal effect of hybridization in allotriploids, and promise a guidance for their commercial production. • First comparison analysis of tetraploid-based natural crossing autotriploid and allotriploid (C. gigas × C. angulata). • DGTA had growth and survival advantages in northern China, while DATG and DATA had advantages in southern China. • The infertility of four triploid groups followed the same decreasing trend DGTG ≥ DGTA > DATG > DATA. • Site, genotype and their interaction always had significant effects on growth. • DGTA in northern and DATG in southern China could be commercial promotion as excellent new strains. [ABSTRACT FROM AUTHOR]

The oyster aquaculture industry in the USA, especially the Chesapeake Bay, has shown rapid growth over the last decade. Breeding has played a large role in this growth in the Chesapeake Bay, with emphasis on the selection for disease resistance, growth and the development of triploid Crassostrea virginica . With major gains realized in both of these traits, we are attempting to add more, such as, compositional traits. A specific interest for the Aquaculture Genetics and Breeding Technology Center is to derive compositional data for use with our selective breeding program. Near Infrared Reflectance Spectroscopy (NIRS) estimates of moisture and glycogen may lead to the definition of these new traits for selection to accompany those traditional measures of survival, meat yield, and growth rate. This study describes the development of NIRS models to estimate moisture and glycogen in the eastern oyster C. virginica . NIR spectra of 138 homogenized oyster meats were modeled against physicochemically measured moisture and glycogen data. The robustness of resulting models was assessed by an independent validation that showed a high coefficient of determination for validation (R 2 val = 0.95) and high residual predictive deviation (RPD ≥ 4.1) for both parameters, making them suitable for quantification. In a second step, these models have also been validated to obtain compositional data on different levels of ploidy in C. virginica (diploid, triploid, and tetraploid). These parameters will be applied to our family based selection program where heritabilities will be calculated. Statement of relevance For the first time we have developed NIRS models to determine compositional analysis in C. virginica . NIRS estimates of moisture and glycogen may lead to the definition of new traits for selection to accompany other traditional measures (survival, meat yield, and growth rate). NIRS measurements will be applied to our family based selection program where heritabilities will be calculated. [ABSTRACT FROM AUTHOR]

Cytochalasin B (CB) has been used to induce tetraploidy in oysters since the practice began in 1993. However, CB is toxic and presents health risks to hatchery workers who administer the treatment. 6-dimethylaminopurine (6-DMAP) is also an effective cytokinetic inhibitor, and does not carry the health risks of CB. We examined the relative effectiveness of 6-DMAP vs CB for producing tetraploids in the Eastern oyster ( Crassostrea virginica ). Survival and yield of tetraploids varied widely among the 15 experiments. Larvae resulting from 6-DMAP treatment had higher survival in 11 of the 14 trials on day two and day six/seven. For yield of tetraploids, 10 of 13 6-DMAP treatments had higher proportions of tetraploids on day two and at the second sampling – day six, seven, or nine – 7 of 10 had higher proportions of tetraploids. Tetraploid spat were obtained from the majority of surviving cultures. Based on these results, 6-DMAP can effectively replace CB for inducing polyploidy in C. virginica , and probably other Crassostrea spp. , due to the success of the treatment, the ease of application, and the reduction in health risk to hatchery workers. This study set the precedent for the use of 6-DMAP on C. virginica and established a new procedure for inducing tetraploids using triploid eggs. It might be possible to refine the treatment to further optimize yield of tetraploids. Statement of relevance In this manuscript we report a novel method of inducing tetraploid Crassostrea virginica from triploid eggs using 6-dimethylaminopurine. We compare the efficiency of cytochalasin B and 6-dimethylaminopurine for tetraploid induction. We also report the expected fecundity of triploid C. virginica females. The method of tetraploidy induction we report here will likely be useful for inducing tetraploidy in other Crassostrea spp. [ABSTRACT FROM AUTHOR]

Slow growth and genomic instability are the main problems facing tetraploid oyster breeding. In response to the above problem, we developed tetraploid by using Crassostrea gigas 'Haida No.3', a new variety with rapid growth and black shell color, and analyzed the growth, survival and ploidy of diploid ♀ × diploid ♂ (DD), diploid ♀ × tetraploid ♂ (DT: triploid) and tetraploid ♀ × tetraploid ♂(TT) in different periods. The results showed that there was no significant difference between the fertilization rate of DD, DT and TT, but the hatching rate of TT was significantly lower than that of DD (P < 0.05). The shell height of TT was significantly lower than DD, and the shell height of DT was significantly higher than that of DD at 13 days (P < 0.05). The survival rate of TT was lower than that of DD and DT in larval stage (P < 0.05), while there was no significant difference in the mean survival rate of DD, DT and TT in juvenile stage. The tetraploid rate in TT was 100% during the larval and juvenile stages. The shell color of all progeny in TT and DT was black and consistent with C. gigas 'Haida No.3'. These results indicated that black shell color of C. gigas 'Haida No.3' could be stably passed on to triploid and tetraploid offspring, suggesting that establishing genomically stable tetraploid populations was feasible by screening tetraploid parents. • The growth, survival and ploidy of diploid, triploid and tetraploid Pacific oysters were examined. • The growth rate of triploid (diploid ♀ ´ tetraploid ♂) was higher than that of diploid and tetraploid from day 13. • Black-shell color trait could be inherited stably in tetraploid offspring. [ABSTRACT FROM AUTHOR]

Use of all-female triploids (3N) instead of diploids (2N) can be advantageous in rainbow trout ( Oncorhynchus mykiss ) aquaculture and fisheries management due to sterility and the consequent superior growth and feed conversion achieved at reproductive age. Triploid trout are currently produced by pressure or temperature shock of the zygote (induced-triploid, 3NP). An alternative procedure to create triploids that may have fewer negative effects on embryonic development and result in 100% triploids is to mate a tetraploid (4N) parent with a 2N parent (intercross-triploid, 3NC). We compared growth performance of nine sets of families each consisting of 3NP, 3NC, and 2N siblings through two years of age. The 2N and 3NC fish exhibited greater body weight than the 3NP fish throughout most of the study; however, by the end, body weight of the 3NC fish exceeded that of the 2N and 3NP fish, which were similar. Condition factor was lowest for 3NC and highest for 3NP fish throughout most of the study. Higher rates of vertebral compression in the 3NP fish affected body weight, fork length, and condition factor in this group. The correlations of body weight among families for the three ploidy types ranged from R 2 below 0.03 around 8–9 months post-hatch, to above 0.5 around 18–19 month post-hatch, supporting family differences in growth response to triploidization and triploidization strategy. Nevertheless, a greater correlation between 2N and 3NC values than 2N and 3NP values, particularly at body weights above 1 kg, supports greater potential to improve 3NC growth performance compared to 3NP performance when genetic selection is based on the 2N phenotype. [ABSTRACT FROM AUTHOR]

Tetraploid Pacific oysters ( Crassostrea gigas ) are commonly used within aquaculture to generate predominantly sterile triploids for commercial use. Unlike triploids, tetraploids are fertile and can be spawned with each other to maintain a commercial breeding population. The impacts this hatchery perpetuation has on the genetic diversity of the tetraploid population and subsequent commercial triploid product are currently unknown. This study determines the diversity (number of alleles and heterozygosity), pedigree assignment and effective population size over two generations of tetraploid production. A significant drop in diversity was observed over two successive generations of tetraploid oysters spawned in 2008 and in 2011, likely due to different numbers of broodstock used. Similar to diploids, pedigree assignment in tetraploids showed unequal parental contributions and an effective population size smaller than the census population, thus the potential for inbreeding to occur in the future is high. [ABSTRACT FROM AUTHOR]

Advantages associated with sterility in triploids have made them the standard for commercial aquaculture of Crassostrea virginica in the Chesapeake Bay. Current hatchery practices for commercial production of triploids employ tetraploids as broodstock, and thus tetraploids are a core asset for oyster culture. Tetraploids undergo reversion, losing entire sets of chromosomes, and become heteroploid mosaics comprised of triploid and tetraploid cells. The possible effects of using mosaic tetraploids for triploid production are a practical concern for commercial oyster culture. We crossed mosaic and non-mosaic tetraploids, males and females, to a reference diploid oyster and compared relative DNA content and phenotypic qualities of triploid progeny. Relative DNA content was measured in somatic and gametic tissue of tetraploid broodstock, as well as in resulting triploid larvae via flow cytometry. Size, abnormality, and survival of larvae were recorded through the rearing process. For six crosses, triploids were raised for 1 year and shell metrics, size, and somatic DNA content were compared. Flow cytometry analysis of broodstock revealed sperm from mosaic tetraploids were consistently di-haploid and virtually indistinguishable from sperm of non-mosaics. For resulting triploid progeny, there were no detectable differences between larvae or juveniles produced from mosaic and non-mosaic tetraploids. Differences existed, however, between triploid larvae produced from di-haploid sperm and those produced from tetraploid eggs: triploids from tetraploid eggs were significantly more abnormal, less viable, and grew slower. Our findings support current commercial practices of using tetraploid males as the principal parent for triploid production and demonstrate no practical consequence from using mosaic tetraploid broodstock for commercial production of triploid C. virginica . Further analysis via cytogenetic techniques may provide insight into long term consequences of using mosaic tetraploids, for example, in tetraploid × tetraploid crosses. [ABSTRACT FROM AUTHOR]

Crassostrea gigas is an important species of oyster culture in northern China, which has important economic value. In recent years, triploid cultivation of C. gigas has gradually emerged because of the advantages of poor fertility and fast growth, but the comparative studies on tetraploid, triploid and diploid C. gigas are not comprehensive and systematic. In addition, forward or reverse mating tetraploids and diploids all can produce triploids, it is necessary to compare the performance of the two triploid groups. This study was conducted to understand the growth, survival, ploidy level and fertility of tetraploids in China, and to figure out how to mass-produce triploids. Aritificial hybridization was made between diploid (D) and tetraploid (T) to produce DD, TD, DT and TT groups (males are listed first). The results showed that the fertilization rate, cleavage rate, D larval rate and larvae survival rate of TD group were significantly higher than those of DT and TT groups, and the larval growth of TD group was significantly faster than that of the other three groups. In cultivation period, the growth and survival rate of TD in the 2 sites were significantly higher, and the 100% triploid rate was stable. In addition, some triploids in TD and DT groups were fertile and could produce functional gametes. But the proportion of female and hermaphrodite in fertile triploids was higher than that in diploids and tetraploids, and the fertility of triploids was still poor overall. However, some tetraploids in TT group would lose chromosomes during growth and become triploids, diploids or aneuploids. Tetraploid had the slowest growth and the lowest survival rate at the both sites, but its fertility was normal and could produce a large number of functional gametes, which could provide sufficient sperm for large-scale production of triploids. All these data support tetraploid ♂ × diploid ♀ is a good strain for commercial promotion in China. In conclusion, this study provides comprehensive data for understanding the performance of tetraploid and the aquaculture potential of triploid C. gigas , and also supports the commercial promotion of triploid C. gigas (tetraploid ♂ × diploid ♀) in China. • A comprehensive comparative analysis on DD, TD, DT and TT of C. gigas was conducted, and found some new results. • Tetraploid C. gigas had chromosome loss, and the true tetraploids had the traits of slow growth, low survival rate and normal fertility. • Parental orgin and environment could affect the growth, survival, fertility and ploidy composition of progeny. • TD with the best performance could be used as an excellent new strain for commercial promotion in China. [ABSTRACT FROM AUTHOR]

Tetraploid of Crassostrea gigas was first reported in the 1990s, but its biological characteristics are seldomly known. To understand the adaptation of tetraploid larvae to salinity and temperature, the effects of salinity treatments (10, 15, 20, 25 and 30 psu) and temperature treatments (18, 23 and 28 °C) on the growth and survival of tetraploid and diploid larvae were comparatively studied. In salinity treatments, the accumulative survival rate (ASR) and relative growth rate (RGR) of tetraploid larvae were generally lower than that of diploid larvae (P < 0.05). The maximum ASR and RGR of tetraploid larvae occurred at 30 psu, with the values of 41.09% and 152.91%, respectively. At day 16, the maximum difference in ASR between diploid and tetraploid larvae was 36.41% at 20 psu, and the maximum difference in RGR of diploid and tetraploid larvae was 62.36% at 10 psu. The ASR and RGR of tetraploid larvae were lower than that of diploid larvae under temperature treatments (P < 0.05). The maximum ASR and RGR of tetraploid larvae occurred at 28 °C, with the values of 19.67% and 235.40%, respectively. The ASR of both diploid and tetraploid larvae decreased sharply in the first four days. The RGR of larvae at 18 °C was much lower than that at 23 °C and 28 °C (P < 0.05). Hence, a salinity range of 25–30 psu and a temperature range of 23–28 °C are suitable culture conditions for tetraploid larvae. These results indicate that the natural environment conditions can meet the temperature and salinity requirements for the survival and growth of tetraploid larvae. However, tetraploid larvae are less adaptable to temperature and salinity than diploid larvae. The environmental adaptability of tetraploid needs further improvement. • The temperature and salinity adaptation of tetraploid larvae of Crassostrea gigas were evaluated for the first time. • Tetraploid larvae were generally less adaptable to temperature and salinity than diploid larvae. • Natural environmental conditions can meet the requirements for the survival and growth of tetraploid larvae. [ABSTRACT FROM AUTHOR]

Abstract: All-female triploid fish are advantageous in rainbow trout (Oncorhynchus mykiss) aquaculture due to sterility and the consequent superior filet quality, growth, and feed conversion achieved at reproductive size. Triploid fish are commonly produced by pressure or temperature shock of the zygote (induced-triploids, 3NP), but can also be produced by mating a tetraploid parent with a diploid (2N) parent (intercross-triploids, 3NC). Little is known about the disease resistance of 3NC fish. In this study, we measured post-challenge survival of genetically-related 2N, 3NP and 3NC families after exposure to Flavobacterium psychrophilum the etiological agent of bacterial cold water disease (BCWD). The families used in this study originated from either an unselected commercial stock or BCWD resistant or susceptible line of rainbow trout. The overall survival of 2N fish was slightly higher than the respective 3NP and 3NC fish. Although 3NC fish tended to show higher survival than 3NP fish, this response was not sufficiently consistent to promote intercross production of triploids for increasing disease resistance. The survival of ten sets of 3NP, 3NC and 2N families, created from BCWD resistant and susceptible line parents, demonstrated overall similar inherent relative survival differences among the ploidy types both among families and between lines, although family differences in response to triploidization and triploidization strategy were observed. In summary, minimal survival difference between 3NP and 3NC families following experimental challenge suggests that innate resistance to F. psychrophilum is not substantially altered by the triploidization strategy and progress in family-based selective breeding of diploid fish for BCWD resistance will substantially translate into improved survival when triploids are derived either by shock treatment or intercross breeding. [Copyright &y& Elsevier]

Abstract: Tetraploidy is induced in rainbow trout by applying a pressure shock at a specific time point between insemination and first cleavage, or the first cleavage interval (FCI). Previous studies suggested that variation in the FCI among individuals and populations of fish prevents the identification of a single time point that can be used for all trout. In this study we confirmed the optimal time to apply pressure is 65±5% of the FCI. In addition, we found that variation in FCI of fish from a common environment can be within limits that allow a single time point to be established for that group of fish, if ova post ovulatory aging is taken into account. Aging of ova, either in vivo or in vitro, increased FCI to a degree that is a concern for tetraploid induction. The FCI was about 12min longer at 7days post ovulation, and 30min at 10–14days, than at 1day. The FCI for a group of fish was consistent throughout the spawning season. Survival to hatching and frequency of spinal abnormalities were similar for progeny of first and second generation tetraploid males, but survival was doubled and abnormalities reduced by approximately 90% in second generation tetraploid females compared with first generation females. All progeny of tetraploid by tetraploid crosses were determined to be tetraploids based on flow cytometry of embryonic cells. In summary, attention to ova aging and use of second generation female tetraploids allows efficient production of a tetraploid rainbow trout broodstock. [Copyright &y& Elsevier]

Abstract: Heat shock is an effective and widely used method for polyploid induction in fish, but has not been well studied in molluscs. In this study, heat shock was tested for polyploid induction through meiosis or mitosis inhibition in the dwarf surfclam, Mulinia lateralis Say. To determine the most effective temperature, different heat shocks (32, 35 and 38 °C) were applied to newly fertilized eggs at 8–11 min post-fertilization (MPF) to inhibit the extrusion of polar body 1 (PB1), and ended when the second polar body began to form in control groups. Ploidy of resultant larvae was determined by flow cytometry (FCM). Both 35 °C and 38 °C were effective in inhibiting PB1, but 38 °C led to complete mortality of larvae. Heat shock of 32 °C only accelerated embryonic development without inhibiting PB1, as all resultant larvae were diploid. High percentages of triploids (86.3–98.5%) were produced by the 35 °C treatment as detected at the juvenile stage. Different durations (10, 15 and 20 min) of the 35 °C heat shock were used for PB1-inhibition to test effects on polyploid formation, which produced primarily triploids (10 min) and pentaploids (20 min), but virtually no tetraploids. To inhibit mitosis I (M1) and mitosis II (M2) for tetraploid induction, a heat shock of 35 °C was applied to fertilized eggs at 35–37 and 50–57 MPF for about 20 min, producing up to 82.8% and 44.4% tetraploid larvae, respectively. Most tetraploid larvae were abnormal and did not develop to the D-stage, and no tetraploids were observed at the juvenile stage. This study shows that heat shock is a highly effective method for polyploid induction in the dwarf surfclam and possibly in other molluscs also. [Copyright &y& Elsevier]

Abstract: Spermatozoal ultrastructure of tetraploid Pacific oysters, Crassostrea gigas, was examined by light and electron microscopy and compared to that of diploid Pacific oysters. Ultrastructure of sperm from tetraploids was compositionally similar to diploids except for overall size and the number of mitochondria. Instead of the four mitochondria always found in sperm from diploid oysters, 44% of sperm from tetraploid oysters had four mitochondria, 53% had five, and 3% had six. The linear dimensions of sperm components such as acrosome height and width, sperm head length and width, mitochondrial height, length of the main piece and end piece of flagellum, and total length of flagellum in tetraploids were approximately 1.25 times larger than corresponding measurements in diploids, which corresponds to a doubled volume in sperm of tetraploids compared to that of diploids. Tetraploid males produced half the number of sperm (2.7±0.5×1010) g− 1 of gonad wet weight compared to diploid males. Despite the increased sperm sizes in tetraploids, the ratios of the sperm head length to head width, and sperm head length to flagellum length were the same for both ploidy levels for fixed and live samples. The implications of these findings on susceptibility of sperm from diploid and tetraploid oysters to damage from cryopreservation are discussed. [Copyright &y& Elsevier]

Abstract: Alterations of chromosome number have been observed in the somatic tissue of Crassostrea gigas diploids and artificial polyploids. Tetraploid oysters with abnormal chromosome numbers in some or all of their tissue are considered undesirable as parents either for triploids (produced via a cross with diploids and of aquacultural interest) or for tetraploid breeding. Aneuploid tetraploid oysters may confer the tendency to lose chromosomes and to revert to lower ploidy levels to their offspring. More directly, their offspring could have a lower ploidy because of potential links between somatic and gametic chromosome loss. The present study evaluated the phenomenon in six bi-parental tetraploid families bred from parents of differing somatic ploidy quality. The offspring were assessed over a year using chromosome counts. Differences between families and parental influence on chromosome loss were evaluated. This showed that chromosome loss occurred at high frequency in all families and that families differed in their composition of ploidy types. Triploidy was observed in four out of the six families. Comparison of data collected at 4 months and 1 year showed no worsening on this time-scale. The incidence of chromosome loss among families suggests a genetic basis to the phenomenon, although a direct relationship between the ploidy quality of the parents and that of the offspring was not observed. The origins and evolution of chromosome loss in polyploid oysters and the implications for breeding are discussed. [Copyright &y& Elsevier]