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1.
The Hong Kong oyster (Crassostrea hongkongensis) and the Portuguese oyster (Crassostrea angulata) are important aquaculture species in southern China. To understand the potential feasibility of hybridization between the two species, two‐by‐two factorial cross‐experiments were conducted in Shenzhen (Guangdong province). An asymmetry in fertilization was revealed: C. hongkongensis eggs could be fertilized by C. angulata sperm, but the reciprocal cross was not possible. The fertilization and hatching success in the C. hongkongensis females × C. angulata males (HA) cross was lower than the two intraspecific crosses. Moreover, hybrid larvae had a slower growth rate than those from parental progenies due to genome incompatibility. However, the size of the spat and adult growth were greater than those of the two parental progeny, with obvious heterosis during the grow‐out stage. The survival advantage of hybrids was examined at all times. The surprising finding was that all hybrids were completely fertile, meaning they could produce normal and functional gametes. Genetic analysis by molecular markers was applied to confirm that the HA spat were true hybrids. Our results revealed that the interspecific hybridization between C. hongkongensis and C. angulata is completely successful in one direction. Furthermore, hybrids are viable, fast growing and completely fertile, which provides a promising method for the genetic improvement of oysters as a new aquaculture stock in southern China.  相似文献   

2.
The Hong Kong oyster, Crassostrea hongkongensis is an economically important and widely cultivated oyster species in southern China. Aiming to improve the aquaculture potentials of C. hongkongensis, a triploid organism was generated by inhibiting the second polar body formation in the fertilized eggs, using 0.5 mg L?1 cytochalasin B. Triploids exhibited significantly higher growth and were larger than the diploids throughout the life cycle. Much of the triploid growth advantage can be attributed to resource reallocation to structural development due to gonadal sterility. Most of the triploid oysters exhibited polymorphic sterility with atrophic gonads and abnormal gametogenesis. Only few ‘dysfunctional’ sperms were produced by the triploid males, thus ruling out reproductive and genetic contamination of natural oyster populations from triploid cultivations. This advantage in addition to the superior growth of triploids makes it a potent alternative in Hong Kong oyster aquaculture industry. Triploid survival was mostly found to be similar to that of diploids except for day 360, when a significant triploid advantage in terms of survival was noted. Furthermore, we found that growth and survival of Hong Kong oyster is significantly higher at the Zhuhai site in comparison to the Beihai site. Our results indicate a strong environmental effect in Hong Kong oyster cultivation and points to the fact that Zhuhai site was more suitable for oyster farming than the Beihai site. Overall, this study provides valuable information to the aquaculture industry of southern China.  相似文献   

3.
郭香  郑雅友  曾志南  巫旗生  宁岳  祁剑飞 《水产学报》2018,42(11):1711-1718
2015年9月–12月,以菲律宾蛤仔福建养殖群体和广东野生群体子一代为亲本,开展了双列杂交实验,建立了两个自交组和两个杂交组,研究了杂交子代幼虫和稚贝的生长与存活的杂种优势。结果显示,各实验组均有较高的受精率和孵化率,但无显著差异。总体上,幼虫期的生长受母体效应影响显著,稚贝期的生长杂交效应主要受交配方式影响。相反,幼虫期的存活受配对方式影响最显著,稚贝期的存活受卵源影响显著。在幼虫期,杂交组与自交组在生长和存活方面差异不显著。在稚贝期,生长表现出明显的杂种优势,壳长和壳高在30日龄以后,正反交组的平均生长速率显著快于自交组。在40日龄时,壳高和壳长总杂交优势值达到最大,分别为25.64和27.00。这可能是因为杂种优势的表达具有时期差异性。在幼虫期,福建自交组表现出最高的存活率,为36.45%±1.85%;稚贝期,广东自交组存活率最高,为52.27%±2.13%。在幼虫期和稚贝期的存活率方面,未观测到杂种优势,这可能是由于两个杂交亲本群体与存活相关的基因频率无差异或者检测次数较少所致。  相似文献   

4.
长牡蛎3种壳色家系间杂交子代生长和存活比较   总被引：5，自引：1，他引：4  
为了利用杂种优势培育长牡蛎优良新品种,实验以3种不同壳色长牡蛎家系(白色/W、黑色/B、紫色/P)为材料,采用3×3完全双列杂交法,建立了3个自交组合和6个正反杂交组合,分析了各实验组幼虫期和养成期的生长、存活以及杂交子代的杂种优势。结果表明,浮游幼虫期,杂交组PB表现出显著的生长优势;与自交组相比,各杂交组均有着较高的幼虫存活率;在幼虫存活率方面,所有杂交组均有较高的杂种优势率。在养成期,紫壳色自交组的壳高显著大于白壳色和黑壳色自交组;6个杂交组中,PB的壳高生长最快,BP次之,PW、WP的生长最慢;各杂交组与自交组的成活率差异均不显著;杂交组BP及其反交组PB的壳高、壳长、总重和存活率的杂种优势率分别介于3.71%~15.27%、-2.00%~13.10%、11.23%~41.56%、-2.77%~9.83%,其他4个杂交组在整个养成阶段没有表现出杂种优势。  相似文献   

5.
The Kumamoto oyster (Crassostrea sikamea) and the Portuguese oyster (C. angulata) are important aquaculture species which naturally coexist along the southern coast of China. To understand the potential feasibility of hybridization between the two species, we conducted two‐by‐two factorial cross‐experiments in Beihai (Guangxi province), and also compared the survival and growth of the hybrids to that of the two parental progenies during the grow‐out period from July 2014 to July 2015. Genetic analysis confirmed that the hybrid spats were true hybrids. Additionally, the biochemical composition of the 1‐year‐old oyster progenies was determined. In July 2015, the mean shell height of the hybrids was 42.98 ± 6.29 mm, which was higher than that of the Kumamoto oyster progeny. The cumulative survival rate of the hybrids was 26.37 ± 1.32%, which was higher than that of the progeny of the Portuguese oyster. Mean lipid content of the hybrids was 13.65 ± 1.63% of dry weight, which showed obvious heterosis compared to those of the two parental progenies. Observation of gonads revealed that all hybrids were completely fertile. Furthermore, relative expression of the lipid homeostasis genes, SREBP (sterol regulatory element‐binding proteins), PPARα (peroxisome proliferator‐activated receptor) and INSIG (insulin‐induced gene) were found to vary between parental progenies and the hybrids, thus providing a possible reason for difference in the lipid contents of these experimental groups. Overall, the hybrids were viable, rich in lipid and completely fertile and thus could serve as a promising aquaculture stock for oyster breeding in southern China.  相似文献   

6.
Cod stocks in the North Sea, including the Kattegat and the Skagerrak, have declined dramatically since the 1970s. Occasionally there is a high recruitment of juveniles in Kattegat/Skagerrak, without leading to the rebuilding of adult cod stocks despite reduced fishing mortality. In a biophysical model of egg and larval drift, we examined the potential importance of extant and historical spawning grounds for recruitment of cod in the Kattegat/Skagerrak seas using data of spawning stock biomass from the 1970s and from today's reduced stocks. The results suggest that Kattegat in the 1970s relied on largely locally retained (83%) larvae with little annual variation in recruitment. Kattegat also provided a substantial proportion of larvae recruiting in Swedish Skagerrak (72%). This is in contrast to present conditions where the Kattegat spawning stock has been reduced by 94%, and Kattegat only provides 34% of locally retained larvae and 30% to Swedish Skagerrak. Instead, the protected area in the Öresund and the Belt Sea are expected today to provide most larvae recruiting in Kattegat. Also, the inflow of larvae from the North Sea to Skagerrak and Kattegat can be significant although highly variable between years, with a positive correlation to the North‐Atlantic Oscillation index (NAO). The rebuilding of healthy spawning areas in the Kattegat may be key for restoring local cod stocks in both Kattegat and along the Skagerrak coast. This poses a management challenge if cod with local ‘Kattegat’ adaptations, e.g., in terms of egg density and migration patterns, are lost or reduced to non‐resilient densities.  相似文献   

7.
栉孔扇贝中国种群与日本种群杂交一代的早期生长发育   总被引：27，自引：4，他引：27  
常亚青 《水产学报》2002,26(5):385-390
对两个不同地理种群的栉孔扇贝的两个群体———中国种群(C)和日本种群(J)的纯种后代及其正反两个杂交组合(C♀×J♂和J♀×C♂)的杂种个体,早期(10月龄)同地同期生长发育进行了测定和统计分析比较。结果表明,两个种群正、反交杂种一代在壳高、壳长、壳宽、活体重及成活率5个生长发育指标上均表现不同程度的杂种优势,反交杂种F1′除成活率外,其余各项生长发育指标显著优于正交杂种;中国和日本两个亲本群体各个性状的测定性能表现为壳宽差异显著和成活率差异极显著外,其它各项指标均没有显著差异。实验证明杂交是提高扇贝生产性能和抗逆性的重要途径。  相似文献   

8.
Comparative studies were made on the growth and biometric relationships of the pearl oyster Pinctada fucata (Gould) Tuticorin stock at (Tuticorin (TST) – parent stock) transplanted from the Tuticorin Bay (8.7°N; 78.2°E) in the Gulf of Mannar along the Indian southeast coast to Kollam Bay (8.8°N; 76.5°E) in the Arabian Sea along the Indian southwest coast (Tuticorin stock at Kollam (TSK) – transplanted stock). At the time of transplantation, Kollam Bay did not have a native stock, however, within a year, the transplanted stock spawned and oyster spats were collected from within the farm (Kollam stock (KS) – progeny stock). The growth in dorso‐ventral measurement and total weight in Kollam Bay was 1.4–1.6 times and 3.1 to 6.8 times respectively greater than that observed at Tuticorin. Furthermore, at Kollam Bay, the thickness observed at the end of first year was similar to that obtained at the end of second year in Tuticorin. Both the TSK and KS had significantly higher instantaneous growth rates (IGR) than TST. All the stocks displayed significantly different biometric relationships. The increased growth in Kollam Bay is attributed to the almost double productivity in the Arabian Sea compared with the Bay of Bengal. It is concluded that in the case of P. fucata, the site and its interaction with environment are important determinants of growth and shell dimensions. The present study clearly indicates that the environmental conditions prevailing along the southeast Arabian Sea are congenial for the growth, gametogenesis, spawning and settlement of P. fucata larvae. In spite of strong monsoonal influences in the hydrology of Kollam Bay, the growth and reproduction of P. fucata stocks indicates its relative hardiness and ability to adapt to a changed environment.  相似文献   

9.
We applied a physiological individual‐based model for the foraging and growth of cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) larvae, using observed temperature and prey fields data from the Irish Sea, collected during the 2006 spawning season. We used the model to estimate larval growth and survival and explore the different productivities of the cod and haddock stocks encountered in the Irish Sea. The larvae of both species showed similar responses to changes in environmental conditions (temperature, wind, prey availability, daylight hours) and better survival was predicted in the western Irish Sea, covering the spawning ground for haddock and about half of that for cod. Larval growth was predicted to be mostly prey‐limited, but exploration of stock recruitment data suggests that other factors are important to ensure successful recruitment. We suggest that the presence of a cyclonic gyre in the western Irish Sea, influencing the retention and/or dispersal of larvae from their spawning grounds, and the increasing abundance of clupeids adding predatory pressure on the eggs and larvae; both may play a key role. These two processes deserve more attention if we want to understand the mechanisms behind the recruitment of cod and haddock in the Irish Sea. For the ecosystem‐based management approach, there is a need to achieve a greater understanding of the interactions between species on the scale a fish stock is managed, and to work toward integrated fisheries management in particular when considering the effects of advection from spawning grounds and prey–predator reversal on the recovery of depleted stocks.  相似文献   

10.
为了获得优良熊本牡蛎(Crassosrea sikamea)种质资源,于2015年从美国Taylor贝类养殖公司引入熊本牡蛎,采用2种配对方式构建了核心基础群体;以中国熊本牡蛎选育群体为对照,评估了美国熊本牡蛎引种的生产性能及可行性。结果表明,美国熊本牡蛎相对于中国群体而言,表现出生长较快,商品规格比率较高,但存活力较低的特点。经过1周年养成,美国熊本牡蛎较中国群体子代壳高提高了11.48%,总重提高了48.12%。评估表明,群体来源对子代生产性能造成了显著的影响,而配对策略尚未产生显著影响。本研究发现美国熊本牡蛎在中国华南沿海具有较好的生产性能,这为熊本牡蛎种质改良提供了宝贵的繁育材料,也为华南牡蛎产业提供了一个可选择的优良品种。  相似文献   

11.
太平洋牡蛎与近江牡蛎的种间杂交   总被引：9，自引：4，他引：5  
为了评估太平洋牡蛎与近江牡蛎能否产生远缘杂种优势,于2010年5月,以成熟的两种牡蛎亲本为材料开展了2×2远缘杂交研究,由长牡蛎自繁组GG(Crassostrea gigas♀×C.gigas♂)、近江牡蛎自繁组AA(C.ariakensis♀×C.ariakensis♂)、正交组GA(Crassostreagigas♀×C.ariakensis♂)、反交组AG(C.ariakensis♀×C.gigas♂)4个实验组组成。分析了子代早期表型性状和杂种优势,并对杂交子代进行了遗传鉴定。结果表明:GA杂交组与AG组的受精强度具有不对称性。幼虫浮游期间,表型性状的中亲杂种优势几乎为0,GA组生长与存活性状表现出积极的单亲杂种优势,而AG组则具有明显的远交衰退现象;幼虫早期表型性状受到母本效应影响,而后减弱。变态期间,GA组变态率较高,得到了大量杂交稚贝;而AG组变态率极低,仅获得了72个杂交稚贝。稚贝培育期间,稚贝表现出中亲生长劣势与存活优势;GA组具有明显的单亲生长与存活优势,而AG组则表现出生长劣势并具有一定程度的存活优势。利用复合COI及ITS2鉴定了种间杂交子结果表明:正反交组杂交子均为真正意义上的两性融合杂交子。实验获得了具有显著杂种优势的GA组杂交子,为现有牡蛎的遗传改良提供了新的方向。  相似文献   

12.
壳金长牡蛎自交和杂交家系生长与存活比较   总被引：2，自引：2，他引：0  
选择具有生长优势的长牡蛎(Crassostrea gigas)G2(A)家系及具有明显生长和存活优势的G19(B)和G28(C)家系进行完全双列杂交,得到包括3个自交组(AA、BB、CC)和6个杂交组(AB、AC、BA、BC、CA、CB)共9个壳金长牡蛎实验组,分析各实验组在幼虫期及稚贝期不同日龄的各生长指标和存活性能,并评估了杂交组的杂种优势。结果表明,在整个培育阶段,大多数杂交组在不同生长时期均表现出较高的生长和存活性能,其中,浮游幼虫期5日龄,所有杂交组的壳高和壳长均显著大于自交组(P0.05);10日龄后,杂交组CB、BC和AC的壳高显著大于相应的自交组(P0.05),杂种优势明显;稚贝期85和130日龄,杂交组CB的壳高性能大于其他实验组。浮游幼虫期10日龄,CB组存活率显著大于AA、CA组(P0.05);稚贝期85日龄后,杂交组AC、CA和CB的存活率杂种优势逐渐增大;190日龄,杂交组AC、BC与自交组AA、CC之间存活率差异显著(P0.05)。研究结果为壳金长牡蛎新品种的培育及杂种优势的充分利用奠定了重要基础。  相似文献   

13.
A diallelic cross between two strains [Layo strain (LS) and Noun strain (NS)] of the catfish Heterobranchus longifilis Valenciennes was carried out under controlled hatchery conditions to estimate their reproductive performance and aquaculture potential in terms of fertilizability, hatchability, survival, growth and heterosis. The average fertilization rate of all mating groups was as high as 90.4%, the fertilization rate of the purebred NS (95.2%) being significantly higher than that of the purebred LS or the reciprocal crosses (P < 0.05). The average hatching rate of all genetic groups was as high as 84.7%, the hatching rate of NS (89.4%) being significantly higher than that of the purebred LS or the reciprocal crosses (P < 0.05). The mean survival rate of all crosses from hatching up to the onset of exogenous feeding stood at 94.2%, without showing a significant difference (P > 0.05) between the crosses. During the larval rearing period, which extended from the onset of exogenous feeding up to 15 days of age, NS displayed a significantly lower growth rate (P < 0.001) than that of the purebred LS and their reciprocal hybrids. There was no significant difference (P > 0.05) in survival rate (mean 84.7%) between the four crosses at the end of the larval rearing period. During the juvenile rearing phase, the mean growth performance of all crossbreds was similar to that of the purebred LS and significantly different from that of the purebred NS (P < 0.001). The final individual weights attained by LS, NS, LS × NS and NS × LS were 3.31, 0.71, 3.97 and 3.66 g respectively. The increase in weight attained by the fast‐growing crossbred LS × NS was 562.2%, 20.4% and 8.7% more than that of NS, LS and NS × LS respectively. The survival rate of NS (57.1%) was significantly lower (P < 0.001) than that of all the rest of the crosses. The crossbreds displayed about 15.1% heterosis in mean body weight relative to the fast‐growing purebred LS. It was concluded that cross‐breeding of H. longifilis strains could be advantageous because of the hybrid vigour in the progeny.  相似文献   

14.
小黄鱼体长-体质量关系和肥满度的年际变化   总被引：5，自引：4，他引：1  
根据1960-2010年渤海和黄海南部春季(4-5月)14个航次底拖网调查资料,采用体长对应平均体质量的方法和相对体质量法,按性别逐年拟合小黄鱼黄海北部-渤海群系和黄海南部群系雌雄群体的体长-体质量关系,计算肥满度,并分析其影响因子.结果显示,在多数年份内,小黄鱼雌雄个体间体长-体质量关系参数b无显著性差异(P＞0.05);参数a和b呈极显著负相关关系(P＜0.01),lga与b的比值受环境影响较小,可能与鱼体密度有关.小黄鱼黄海北部-渤海群系雌雄群体从1960年到2004年以等速生长为主,与1960年相比,参数b在资源严重衰退期和资源恢复初期(1982-1993年)有所增大;黄海南部群系雌雄群体从1960年到2010年以负异速生长为主,参数b在资源严重衰退期和资源恢复初期(1986-1994年)呈减小趋势,20世纪90年代后期开始逐渐升高.小黄鱼黄海北部-渤海群系雌雄群体的肥满度从1960年到2004年总体呈减小趋势;黄海南部群系雌雄群体1986年的肥满度极显著小于对应群体1960年的肥满度(P＜0.01),此后略有升高,但年间差异不显著(P＞0.05).分析认为,在较好的饵料条件下,相对较低的捕捞压力是20世纪80-90年代初期小黄鱼黄海北部-渤海群系雌雄群体呈等速生长的主要原因:而持续的高捕捞压力引起群体中低龄鱼比例增加、体长生长速度加快是黄海南部群系呈负异速生长的主要原因.个体性成熟年龄减小是小黄鱼肥满度呈下降趋势的主要原因,但黄海伏季休渔管理和春季南黄海较高的水温,可能是20世纪90年代中期开始小黄鱼黄海南部群系各群体肥满度略有升高的原因.  相似文献   

15.
The survival of fish eggs and larvae, and therefore recruitment success, can be critically affected by transport in ocean currents. Combining a model of early‐life stage dispersal with statistical stock–recruitment models, we investigated the role of larval transport for recruitment variability across spatial scales for the population complex of North Sea cod (Gadus morhua). By using a coupled physical–biological model, we estimated the egg and larval transport over a 44‐year period. The oceanographic component of the model, capable of capturing the interannual variability of temperature and ocean current patterns, was coupled to the biological component, an individual‐based model (IBM) that simulated the cod eggs and larvae development and mortality. This study proposes a novel method to account for larval transport and success in stock–recruitment models: weighting the spawning stock biomass by retention rate and, in the case of multiple populations, their connectivity. Our method provides an estimate of the stock biomass contributing to recruitment and the effect of larval transport on recruitment variability. Our results indicate an effect, albeit small, in some populations at the local level. Including transport anomaly as an environmental covariate in traditional stock–recruitment models in turn captures recruitment variability at larger scales. Our study aims to quantify the role of larval transport for recruitment across spatial scales, and disentangle the roles of temperature and larval transport on effective connectivity between populations, thus informing about the potential impacts of climate change on the cod population structure in the North Sea.  相似文献   

16.
The pullet carpet shell Venerupis corrugata is an economically valuable species in several European countries, however, nowadays stocks are under high fishing pressure. Hatchery production of juveniles for release is a major contributor to strengthen the stock and consequently improve the sustainability of the natural stocks. This study aimed to determine the feasibility of rearing V. corrugata larvae with different larval densities (10, 40 and 200 larvae per mL) in a recirculating aquaculture system (RAS), compared with the traditional larval rearing methodology (Batch). The mean survival, growth and metamorphic rate of V. corrugata larvae in RAS was higher (11.1%; 71.3 μm; 21.6% respectively) than in the Batch system, in all tested densities. The larval growth was not affected by the initial density until 40 larvae per mL, however, 200 larvae per mL decreased the larval growth in length nearly 54 μm. The larval rearing time was shortened in 2 days in the RAS system. The physical, chemical and microbiologic parameters suggested that the tested densities were not excessive to disturb the biofilter stability of RAS. The V. corrugata larval rearing performed at high larval stocking densities in RAS system present a reduction in the operating costs to produce this species.  相似文献   

17.
Thyroid hormones, 3,5,3′,5′- tetraiodothyronine (T4) and 3,5,3′- triiodothyronine (T3) have been found in the eggs of several teleost species and are potential regulators of larval development, growth, and survival. The purpose of the present study was to determine whether natural variation of T3 and T4 in the eggs of six stocks of walleye, five wild stocks from Kansas, Iowa, Wisconsin, Minnesota, and North Dakota, and a semi-domesticated stock from an Ohio fish hatchery, have an effect on larval performance in mass culture. Immersion studies were conducted with samples of larvae from four of the same stocks at exposure concentrations of 0.01, 0.05, and 0.1 ppm of T3 and T4. Natural egg concentrations of T3 (range from 0.70 to 1.5 ng/g wet weight of egg) were not significantly different among stocks. Although means of T4 concentration among stocks were significantly different (range 0.53–9.27 ng/g), the difference was caused by the exceptionally high concentration for the Wisconsin stock (9.27 ng/g ± 2.20). Performance measures of the Wisconsin stock (Mississippi River), were not related to T4 concentration in that stock. In spite of similarity in concentrations of T4 and T3 in the eggs, there were significant performance differences among the stocks (survival to 21 d, gas bladder inflation, viability, cannibalism, and growth). The immersion studies, however, revealed a significant difference in incidence of cannibalism and temperature units (TU) to 50% mortality (i.e., survival) between the control groups and treatment groups exposed to 0.01 to 0.1 ppm T3 and T4. Survival was extended more than 2-fold longer in larvae immersed in T3 compared with T4. The immersion study indicated that thyroid hormones are potentially regulators of walleye development, but further investigations are needed to determine reasons for differences in larval performance based on natural concentrations in the egg and artificial exposure (immersion).  相似文献   

18.
熊本牡蛎无嵴和多嵴品系生产性状比较   总被引：3，自引：1，他引：2  
为了评估熊本牡蛎左壳放射嵴有无对其生产性能的影响,于2013年5月,以熊本牡蛎湛江群体子一代作为基础群体,筛选出无嵴及多嵴品系,采用繁殖生物学方法,比较了两个品系的表型性状差异。结果显示,野生群体中,多嵴亲本规格略大于无嵴亲本,鲜重、壳重及怀卵量均显著大于无嵴亲本;两个品系的受精孵化参数、D型幼虫大小及变态规格彼此间无显著差异;多嵴品系存活力及生长潜力在幼虫及养成期间显著高于无嵴品系。中间育成期间,湛江及大风江牡蛎养殖区环境对两品系生长性状造成了一定程度影响,表现出明显的环境效应,但是对存活力尚未造成影响。熊本牡蛎左壳放射嵴无相对于有是显性性状,主要受到一对显性基因控制,而多嵴性状是隐性性状,可以稳定遗传。研究为熊本牡蛎多嵴品系培育及其左壳放射嵴遗传机制奠定了坚实的理论基础与实践经验。  相似文献   

19.
The paper reports a study focused on breeding new rapidly growing and heat‐tolerant strains in a commercially important Asian bivalve, Sinonovacula constricta. To breed a new strain of S. constricta with fast growth and high temperature tolerance, complete diallel crosses were carried out using three different geographical culture populations from Zhejiang (Z), Fujian (F) and Guangdong (G) provinces, China. Larval and spat growth and the survival and heat tolerance of spats were compared in detail. The experimental serial growth traits extracted from larval and spat measurements (shell length and shell height) indicated that there was no difference between six hybrid crosses and parental crosses at the larval stage; while at the spat stage, some differences were observed. The hybrid crosses ZF (Z♀ × F♂), ZG (Z♀ × G♂) and FG (F♀ × G♂) outperformed the parental groups in shell length at the end of intermediate culture, with lengths of 21.77 ± 0.28 mm, 21.55 ± 0.29 mm and 21.44 ± 0.20 mm respectively. For spat survival rate, the hybrid cross ZF (Z♀ × F♂) had a significantly larger value (88.89 ± 4.16%) than all the other groups, and the hybrid cross ZG (Z♀ × G♂) had a significantly larger rate than the cross GZ (G♀ × Z♂) and parental crosses ZZ (Z♀ × Z♂) and GG (G♀ × G♂). The hybrid crosses ZF (Z♀ × F♂), ZG (Z♀ × G♂) and FG (F♀ × G♂) exceeded the parental groups in heat tolerance, but there was no significant difference. The growth, survival and heat tolerance results showed that the crosses ZF, ZG and FG in this study were the best hybridization combinations for genetic improvement, which could have significant implications for the development of razor clam aquaculture. This work provides a theoretical basis for breeding new varieties (strains) that grow rapidly and are heat tolerant.  相似文献   

20.
Demography can have a significant effect on reproductive timing and the magnitude of such an effect can be comparable to environmentally induced variability. This effect arises because the individuals of many fish species spawn progressively earlier within a season and may produce more egg batches over a longer period as they get older, thus extending their lifetime spawning duration. Inter‐annual variation in spawning time is a critical factor in reproductive success because it affects the early environmental conditions experienced by progeny and the period they have to complete phases of development. By reducing the average lifetime spawning duration within a fish stock, fishing pressure could be increasing the variability in reproductive success and reducing long‐term stock reproductive potential. Empirical estimates of selection on birth date, from experiments and using otolith microstructure, demonstrate that there is considerable variation in selection on birth date both within a spawning season and between years. The few multi‐year studies that have linked egg production with the survival of progeny to the juvenile stage further highlight the uncertainty that adults face in timing their spawning to optimize offspring survival. The production of many small batches of eggs over a long period of time within a season and over a lifetime is therefore likely to decrease variance and increase mean progeny survival. Quantifying this effect of demography on variability in survival requires a focus on lifetime reproductive success rather than year specific relationships between recruitment and stock reproductive potential. Modelling approaches are suggested that can better quantify the likely impact of changing spawning times on year‐class strength and lifetime reproductive potential. The evidence presented strengthens the need to avoid fishing severely age truncated fish stocks.  相似文献   

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