长牡蛎壳黑和壳白选育群体生长性状的选择效应

为了培育壳色性状优良且生长性状良好的长牡蛎(Crassostrea gigas)新品系,本研究以5个壳黑第四代家系和5个壳白第四代家系的成贝为基础群体,利用截头法对壳高进行选择,构建了壳黑和壳白快速生长系第一代群体,分析了两个选育群体的壳高和活体体重的选择反应、遗传获得和现实遗传力等遗传参数。结果表明,在长牡蛎收获的490日龄,壳黑群体和壳白群体选择组壳高较对照组壳高分别提高(9.83?1.68)%和(9.97?1.87)%,体重分别提高(10.16?3.64)%和(11.36?1.96)%。两选育群体壳高的平均现实遗传力分别为(0.353?0.09)和(0.405?0.111),体重的平均现实遗传力为(0.192?0.080)和(0.244?0.123)。本研究表明壳黑群体和壳白群体具有较大的遗传方差,在对壳高生长速度直接选择的同时实现了对活体体重的间接选育,可继续通过群体选育提高生长速度。本研究结果可以为培育出壳色美观、生长性状良好的长牡蛎优良品种提供科学依据。     

Genetic improvement of Israeli blue (Jordan) tilapia,Oreochromis aureus (Steindachner), through selective breeding for harvest weight

Genetic parameters and selection responses were obtained for harvest body weight of blue tilapia (Oreochromis aureus) from data collected over three generations in a selected population. A total of 18 194 records representing 186 sires and 201 dams were used in the analysis. Within generation heritability estimates for harvest body weight ranged from 0.18 to 0.58. When data from more than one generation were included in the analysis, heritability estimates became more stable (0.33–0.40) and it was 0.33 when all data were included in the analysis. The common full‐sib effect accounted for 10% of the phenotypic variance in the full data set. Heritability for survival from stocking to harvest was estimated at 0.01 and 0.09 in actual units (fitting an animal model) and in the logit (sire model) scale respectively. The genetic correlation between harvest body weight and survival was 0.22 and not significantly different from zero. The total selection response for harvest body weight over the three generations of selection measured as the difference between least‐squares means of selected and control lines was 17.7%. The corresponding figure when response was measured as the difference between mean breeding values of selected and control lines was 19.6%. The average inbreeding coefficient was 0.003 after three generations of selection. These results indicate that there are good prospects for the genetic improvement of harvest body weight in blue tilapia.     

长牡蛎第三代选育群体生长性状的选择效应

为了培育长牡蛎的高产抗逆新品种,实验采用群体选育方法构建了中国、日本和韩国3个种群的快速生长选育系,2007年至今已连续进行了6代选育。本实验对长 牡蛎选育F₃代壳高和活体体质量的增长、选择反应和遗传获得等遗传参数进行了分析。结果表明,从第120日龄开始,中国、日本和韩国3个选育群体的壳高和 活体体质量均显著高于对照组,在420日龄时,平均壳高较对照组分别高13.4%、10.1%和10.5%,平均活体体质量较对照组分别重18.5%、13.4%和11.6%;壳高的平均现实遗传力分别为0.447±0.226、0.471±0.297和0.367±0.167,表明适于对壳高的生长速度进行进一步的选育。长牡蛎中国、日本和韩国选育F3代活体 体质量的遗传获得平均值分别为16.01%±3.82%、15.03%±5.21%和11.57%±5.15%,表明对长牡蛎壳高的生长速度进行选育时,活体体质量的生长速度也得到了明显提高。本研究结果可以为长牡蛎快速生长品系的连续选育提供依据。     

The Sydney rock oyster Saccostrea glomerata (Gould 1850) breeding programme: progress and goals

In 1990, NSW Fisheries initiated a mass selection programme in Port Stephens, NSW, with the aim of breeding faster growing Sydney rock oysters Saccostrea glomerata (Gould 1850). After two generations of selection, an average weight for age advantage of 18% (range 14–23% per breeding line) was achieved. This equates to a reduction of 3 months in the time taken to reach market size. Experiments are planned to determine how much of this 3 months advantage is additive to the 6 months advantage this laboratory has already obtained using triploid S. glomerata. A parallel set of S. glomerata breeding lines was established on the Georges River, NSW, to include selection for resistance to the protistan parasite Mikrocytos roughleyi, the causal agent of winter mortality. The programme was disrupted by the outbreak of QX disease Marteilia sydneyi, another protistan parasite, in 1994. In 1997, the breeding programme was reorganized and expanded. New lines were bred from oysters that had survived both QX and winter mortality. After one generation, a small improvement in resistance to QX has been recorded; however, the exposure of further generations to M. sydneyi will be required to confirm an increase in resistance.     

Evaluation of progeny of fourth generation Sydney rock oyster Saccostrea glomerata (Gould, 1850) breeding lines

The progeny of four 4th generation Sydney rock oyster Saccostrea glomerata (Gould, 1850) breeding lines that were selected for fast growth were compared in a 3‐year farming experiment. Oysters of the most improved breeding line (line 2) reached market size (≥50‐g whole weight) 15 months earlier than non‐selected control oysters (3 years and 5 months). The average reduction in time to market size for oysters of all four breeding lines was 12.5 months.     

Studies on triploid oysters in Australia: effect of initial size on growth of diploid and triploid Sydney rock oysters, Saccostrea commercialis (Iredale & Roughley)

In a 2-year grow-out trial, triploid Sydney rock oysters, Saccostrea commercialis (Iredale & Roughley), from two initial size grades grew faster (in terms of both mean whole weight and shell height) than the equivalent initial size grades of sibling diploids (P < 0.05). Small size grade triploids caught up with and had significantly heavier (P < 0.05) final whole weights than large size grade diploids after a 2-years grow-out period. The initial size grade had a significant effect on final mean whole weight and shell height for both ploidy types. After the 2-years grow-out trial, the final mean whole weights (but not shell heights) of small and large diploids (35.8 ± 0.6 g and 39.4 ± 0.5 g, respectively) were significantly different (P < 0.05). Small and large triploids grew at a similar rate for the first 18 months despite the significantly (P < 0.05) heavier final mean weight of large grade triploids (48.4 ± 0.8 g and 61.2 ± 0.7 g, respectively). The effect of the initial size grade on subsequent growth of both diploid and triploid oysters which was demonstrated in the present study is of significant commercial value to hatchery and nursery operators as well as growers of single seed oysters. In addition, small-grade triploids appeared to be more valuable in terms of potential growth rate than all diploid grades. There was no significant difference in the final percentage triploidy between small and large grade triploids. A large proportion of diploid/triploid mosaicism was detected in adult oysters.     

熊本牡蛎多嵴和无嵴品系F3生长性状的连续选择效应

为进一步检测熊本牡蛎(Crassostrea sikamea)多嵴和无嵴品系F3的连续选择反应,以2个品系F2上选组为材料,开展2个品系F3混合上选研究,评估2个品系F3生长性状的选择反应、现实遗传力及遗传改进量,解析选育过程中选择效应、品系效应及二者交互作用对生产性状的影响。结果表明:多嵴品系F3生长性状具有较高的现实遗传力,表现出较好的遗传改良效果;无嵴品系F3表现出中等现实遗传力水平,但仍具有一定程度的遗传改良潜能。养成期360日龄时,多嵴品系子代壳高、鲜重的选择反应分别为0.70、0.76;现实遗传力分别为0.40、0.43;遗传改进量分别为7.02%、12.29%;无嵴品系的选择反应分别为0.36、0.33;现实遗传力分别为0.20、0.19;遗传改进量分别为3.74%、5.72%。经过双因子分析模型检测发现:品系来源是影响F3生长性状的主要因子,选择效应是次要因子,二者间不存在明显的交互作用。由此可见,随着连续选择的进行,选择反应逐渐降低,品系来源作用增强,本研究为熊本牡蛎遗传改良和新品系培育奠定了基础。     

Response to selection for harvest body weight of Oreochromis shiranus

Realised and predicted responses to selection were obtained for harvest body weight of Oreochromis shiranus from two generations of selection at the National Aquaculture Centre, Domasi, Malawi. The realised response was estimated from the difference in the least squares means of selected and unselected control populations, while the predicted response was obtained from the difference of the mean breeding values between generations. The realised (13.2%) and predicted (14.4%) responses for harvest body weight over the two generations of selection were not significantly different (P > 0.05). The intensity of selection from F₁ to F₂ (0.66) and from F₂ to F₃ (0.59) was low due to availability of few selection candidates per family at harvest caused by mortality, tag loss and the need to form broad heterogeneous multi-strain F₂ and F₃ populations. Within generation, the heritability estimates for the F₁ (0.31 ± 0.09), F₂ (0.31 ± 0.10) and F₃ (0.35 ± 0.11) generations were moderate. Across generation, the heritability estimate was low (0.14 ± 0.27). Within generation, the magnitude of the common full-sib effect was moderate (0.08-0.09) and not significantly different from zero (P > 0.05). However, across generations, the common full-sib effect was high (0.27 ±0.05) and significantly different from zero (P < 0.05). A substantial correlated selection response due to selection for increased harvest body weight was observed for both tagging body weight and for survival from tagging to harvest; for tagging body weight 22.8% from F₁ to F₂ and 15.9% from F₂ to F₃; for survival 7.2% from F₁ to F₂ and 13.8% from F₂ to F₃. The results are discussed in relation to the maximisation of the genetic gain in the future generations while constraining the rate of inbreeding.     

Yields of cultured Pacific oysters Crassostrea gigas Thunberg improved after one generation of selection

Parental families (G₀) in three lines of Pacific oysters were selected based on live weight and meat yields at harvest. The average live weight yield of progeny (G₁) from crossing G₀-selected lines in seven trials was 9.5% greater than that of nonselected control families and live weight yields were significantly greater (ANOVA, P<0.001) in four out of seven trials. The response to selection was greater if G₁ families were tested at the same site as their parents' selection site rather than at a different site, although this effect was only significant for G₁ families of cohort 5 (P<0.01) but not cohort 7 (P>0.05). A significant genotype×environment interaction affected yields in both cohort 5 and cohort 7 (ANOVA; P<0.001). In addition, correlation between the yields of the same families planted at both intertidal and subtidal sites was positive but weak (cohort 5, r=0.30; cohort 7, r=0.35), indicating that selection for high yield in one environment would likely result in a low correlated response in a different environment. Nonetheless, it was possible to identify six families in cohort 5 and four families in cohort 7 that were among the top 10 families at both sites. Further evaluation of families across a wider range of environments is needed to determine if it is possible to substantially improve yields by selecting “generalist” families that perform well along the whole Pacific coast, or whether it will be necessary to select lines that are suited to particular sites.     

Dual disease resistance in a selectively bred eastern oyster, Crassostrea virginica, strain tested in Chesapeake Bay

Selective breeding efforts have yielded oyster strains, Crassostrea virginica, with improved survival and resistance against Haplosporidium nelsoni (MSX); however, because of susceptibility to the oyster pathogen Perkinsus marinus (Dermo), their utility has been limited in areas where the two parasites co-occur. Dual resistance to H. nelsoni and P. marinus was achieved through four generations of artificial selection of wild Delaware Bay oyster progeny at a site in the lower York River, Virginia, USA where both diseases are enzootic. During 1993–1995, survival, growth, and disease susceptibility of third generation Delaware Bay (F₃-DEBY) oysters were evaluated at the York River site in comparison to that of similarly selected third generation James River, Virginia oysters (F₃-JR), and first generation Louisiana oysters (F₁-LA), whose parents were naturally selected in the wild for resistance to P. marinus. During 1997–1999, the performance of F₄-DEBY was evaluated at three sites in Virginia in comparison to two groups of first generation oysters whose parents originated from Mobjack Bay and Tangier Sound, Virginia where both P. marinus and H. nelsoni are enzootic. In the presence of high infection pressure from both H. nelsoni and P. marinus, the F₃-DEBY stock showed significantly higher survival and growth than either the F₃-JR or F₁-LA strain. After 15 months of deployment, 79% of F₃-DEBY, 11% of F₃-JR and 17% of F₁-LA oysters were market size (≥76.2 mm) and cumulative mortality was only 16% in F₃-DEBY as compared to 42% in F₃-JR and F₁-LA. At the termination of the study, F₃-DEBY oysters exhibited 22% lower mortality than the F₁-LA stock, which outperformed the F₃-JR stock. Relative performance in respect to disease varied considerably with sample date; however, average H. nelsoni weighted prevalence varied such that F₃-DEBY1-LA=F₃-JR and average P. marinus weighted prevalence varied such that F₁-LA3-DEBY3-JR. In the 1997–1999 trial, F₄-DEBY oysters experienced 34–61% lower mortality, greater growth rate, and consistently lower prevalence and intensity of P. marinus than either Mobjack Bay or Tangier Sound oysters. H. nelsoni prevalences were very low (<12%) in all three stocks. This is the first study to demonstrate that reduced susceptibility to both P. marinus and H. nelsoni can be achieved through selective breeding.     

Experimental deepwater culture of the Sydney rock oyster (Crassostrea commercialis): IV. Pilot production of faft oysters

Rafts carrying five permanently submerged oyster trays were moored in nine New South Wales estuaries during 1976–1977 to determine how rapidly culled spat oysters (25–29 g whole weight) or seconds (29–40 g) could be grown into first grade (plate) oysters (40–67 g).In the first series of trials results were obtained from seven localities after 3 months summer growth. The average weight increase was 51%; mortality averaged 17%. A further series of trials were conducted for 3 months in autumn at four localities. Weight increases averaged 40% and mortality 8%.The growth rates calculated from weight increases were two to three times greater than those expected from normal intertidal culture traditional of Australia. The estimated time to convert spat to plate oysters was 4 months for summer and autumn crops.     

Experimental deepwater culture of the Sydney rock oyster (Crassostrea commercialis = Saccostrea cucullata): II. Pontoon tray cultivation

Pontoons made from plastic pipe were tested as an alternative to racks for deepwater culture of the Sydney rock oyster. The growth and mortality of oysters permanently suspended in water on trays beneath floating pontoons were compared with oysters on trays in an intertidal zone. For both culled spat (30–31 g whole oyster weight) and seconds oysters (37–39 g) beneath pontoons the growth rate, measured by weight increases, was three times that of oysters on intertidal racks over a 5-month period. Mortality (from unknown causes) was higher beneath the pontoons. The mean mortality of spat oysters was 40% compared with 24% on the intertidal trays, and for seconds oysters was 51% compared with 34%.     

Evaluation of the progeny of the fourth‐generation Sydney rock oyster Saccostrea glomerata (Gould, 1850) breeding lines for resistance to QX disease (Marteilia sydneyi) and winter mortality (Bonamia roughleyi)

The Sydney rock oyster breeding programme began in 1990 and initially focused on faster growth and resistance to winter mortality disease (WM, Bonamia roughleyi) before including QX disease (QX, Marteilia sydneyi) resistance in 1997. Four generations of oysters have now been exposed to these diseases at three sites in the Georges River, NSW, Australia (Lime Kiln Bar, LKB; Woolooware Bay, WB; and, Quibray Bay, QB). Non‐selected control oysters and lines developed at each site (Line 1 – LKB, Line 2 – WB, Line 3 – QB) were placed at the three sites alongside a new QX‐resistant line (Line 4) bred from QX survivors in other NSW estuaries. Line 1 oysters grew to a marketable size (>50 g) in two years with minimal losses following QX disease outbreaks: 28% mortality compared with 97% in controls. Losses in Line 3 oysters selected for WM resistance at QB were reduced by more than half (23% versus 52%). Line 2 performed best at WB, but this line showed excellent resistance to QX at LKB and WM at QB, indicating that breeding for resistance to both diseases is effective. However, selection of oysters for QX did not confer resistance to WM and vice versa.     

Genetic changes during mass selection for growth in Nile tilapia, Oreochromis niloticus (L.), assessed by microsatellites

Two control (C1 or first control generation, and C4 or fourth control generation) and three selected (S1 or first selected generation, S2 or second selected generation, S4 or fourth selected generation) stocks of Chitralada Nile tilapia were analysed for microsatellite variation to determine the effect of size‐specific mass selection on genetic variability. Genetic variation based on five microsatellite loci (UNH123, UNH147, UNH172, UNH222 and UNH216) showed a slightly higher allelic diversity in the selected stocks (7.4–10 alleles) than in the control stocks (6.8–8.8 alleles). Apparent reductions in the mean number of alleles and H_e values were noted in successive generations of both control and selected lines. Significant deviations from Hardy–Weinberg equilibrium because of an excess of homozygotes indicated inbreeding in all control and selected stocks. Although estimated inbreeding levels were not significantly different among selected and control lines based on Welch's t‐tests, the increase in the degree of inbreeding within the selected line was higher (107.9%) than the control line (64.2%) after four generations. The implications of these results on the management and conservation of genetic diversity in improved breeds are discussed, while the importance of monitoring and minimizing inbreeding are likewise emphasized.     

Growth of the European flat oyster in the Mediterranean Sea (Murcia, SE Spain)

Growth of the natural European flat oyster (Ostrea edulis L.) spat from the Mar Menor (Murcia, Spain) was studied in the Mediterranean Sea over 18 months. The oysters were cultured in two types of containers, stackable plastic Galician trays and plastic mesh pots, deployed at a depth of 15 m hung from a long-line. Two size classes of spat were used, Class I spat (initially 53 mm in size and 19 g in weight) and class II spat (initially 31 mm, 4 g). The best results were observed in the class I oysters grown in the trays, which yielded a substantial biomass (24.77 kg m^–2), the survival rate was 69% and commercial size (60 mm) was attained by all the oysters within 9 months of the start of the experiment. The observed growth of the class II oysters was poor, attaining a mean of not more than 50 mm and 18 g; the survival rate ranged between 25–74% and only between 8–13% of the class II spat attained commercial size.     

橙色莫桑比克罗非鱼（Oreochromis mossambicus）和荷那龙罗非鱼（O．hornorum）的选育效果评价

以橙色莫桑比克罗非鱼（Oreochromis mossambicus）和荷那龙罗非鱼（O．hornorum）为基础群体,分别对其进行选育,并对产生的选育系F4代的选育效果进行了评价。经过4代的选育,橙色莫桑比克罗非鱼和荷那龙罗非鱼的日增重率分别比对照系提高了27．96％和36．73％,差异显著（P〈0．05）,平均每代选育效应分别为6．99％和9．18％。F4代的体重变异系数分别为23．74％和22．17％,比对照组分别降低了24．83％和36．33％。而且第一次性成熟时这2种罗非鱼的平均体重都比对照系增加2倍以上,其杂交子代的雄性率达到了99．4％。试验结果表明,橙色莫桑比克罗非鱼和荷那龙罗非鱼的选育效果明显,F4代的生长性能有了显著提高,个体之间的生长速度趋于一致;也说明这2种罗非鱼F4代仍具有一定的选育潜力,对其继续进行选育是切实可行的。     

Experimental deepwater culture of the Sydney rock oyster (Crassostrea commercialis): V. Commercial raft trials

Four large rafts (6.4 × 4.3 m), each costing $ A 543 totally equipped and holding 600 kg of trayed layers of oysters, were sited in New South Wales estuaries during 1977 and 1978. Small, single oysters (spat at 25–29 g whole weight or seconds at 29–40 g) were grown to restaurant (plate) grade (40–67 g).Sixteen crops were harvested, usually after three months growout. None showed evidence of overspatting (attachment of young oysters to the crop). Growth rates (measured as oyster weight increases) ranged from 5 to 30% per month and averaged 19%. In four of the crops mortality was high (12, 22, 22 and 90%) due to parasites, predators or wave action. In the remaining 12 crops natural mortality averaged 6% total for the growout period. The average actual wholesale value of the crops was $ A 422 and this could be raised to an estimated wholesale value of $A 527 per crop by utilising pregrowout grading and harvest date selection. Several husbandry practices are recommended. (1) Grading oysters mechanically before growout to produce more uniform crops. (2) Covering top trays to prevent fish attacks and losses through waves. (3) Deciding optimum harvest date by inspection after three months growth.     

Growth,mortality and reproductive traits of diploid and triploid Pacific oysters (Crassostrea gigas,THUNBERG, 1793) in Southern Brazil

This work aimed to evaluate the whole weight (g), shell height (mm), mortality (%) and reproductive aspects (condition index and histology) of triploid (3N) Pacific oysters (Crassostrea gigas) cultivated in southern Brazil. To accomplish this, a comparative experiment was performed with a diploid (2N) control group in two cultivation sites on Santa Catarina Island: North Bay (NB) and South Bay (SB). Whole weight, height and cumulative mortality were evaluated monthly for eight months and condition index (CI) for six months. Histological analysis was performed every two weeks for four months to investigate reproductive aspects. At the end of the experiment, whole weight and height were similar for 3N and 2N oysters. However, while more growth in whole weight and height was observed in the initial phase of cultivation in NB, such growth was not detected in SB until intermediate and final grow‐out phase. At harvest, cumulative mortality in 3N oysters was similar that in 2N oysters. The results suggest that diploid and triploid oysters grown in southern Brazil have similar developmental patterns based on whole weight and height, as well as reproductive cycle. In addition, cultivation sites have more influence on growth and mortality than ploidy levels.     

Response of Two Generations of Selection to Increased Body Weight in Channel Catfish,Ictalurus punctatus,Compared to Hybridization with Blue Catfish,I. furcatus,Males

ABSTRACT

Two generations of selection for increased body weight in Kansas (AU-KS-2) and Marion (AU-MS-2) lines of channel catfish, Ictaluruspunctatus, resulted in a 12% and 11% increase in body weight at market size, respectively. The second generation of selection produced no improvement in growth, and there was a slight negative response to selection for body weights during the second generation. Cumulative realized h² was 0.17 ±0.03 and 0.15 ±0.03 for AU-KS-2 and AU-MS-2, respectively, based on growth performance measured against a randomly bred, Kansas control for the two generations. Relative size differences were established by the time the fish reached 80 g, and these relative size differences were maintained the remainder of the experiment. Growth rate of the channel catfish ♀ × blue catfish 6, I. furcatus, hybrid was 35% faster than the Kansas control, and better than all three groups of channel catfish. The growth improvement through interspecific hybridization was three times better than through mass selection.     

The impact of successive mass selection on population genetic structure in the Pacific oyster (<Emphasis Type="Italic">Crassostrea gigas</Emphasis>) revealed by microsatellite markers

To evaluate the impact of mass selection on genetic structure in artificially closed populations of the Pacific oyster Crassostrea gigas, we performed mass selection over six generations on two stocks from Japan and Korea and analyzed their temporal genetic variation and structure using 18 microsatellite makers, which were compared with the base populations of the two selected lines and one wild population from China. The average numbers of alleles (Na), mean observed heterozygosities (Ho), and expected heterozygosities (He) varied over generations in the two selected lines (selected lines of Japan, Na = 10.7–14.9, Ho = 0.757–0.846, He = 0.778–0.871; selected lines of Korea, Na = 9.4–17.3, Ho = 0.736–0.865, He = 0.744–0.854). There was no significant reduction in heterozygosity in the two selected lines. However, the average number of alleles per locus was significantly lower in the fifth and sixth generations of the two selected lines compared with that in the base population and wild population (P < 0.05), suggesting that the successive mass selection in closed populations may increase the sensibility of rare alleles to genetic drift. Equalizing the sex ratio of parents and reducing the selection intensity properly with the increase of selective generations is recommended to minimize the deleterious effect of genetic drift and bottleneck caused by successive mass selection. The information obtained in this study is useful for the design of appropriate management strategies for selective breeding of C. gigas.