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排序方式: 共有455条查询结果,搜索用时 62 毫秒
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《Journal Of Applied Aquaculture》2013,25(1-2):75-83
Abstract Most breeding programs for the Australian native freshwater silver perch, Bidyanus bidyanus, are based on fish originally captured from natural populations. However, over the last 20 years, there has been a dramatic decline in the distribution and abundance of silver perch in the wild and the species now has the conservation status of “vulnerable.” Unless broodfish can be domesticated a serious shortage is imminent. The aims of this study were to determine the age and size at sexual maturity and the reproductive performance of silver perch reared in captivity. Fingerlings (mean weight, 4.0 g) from a hatchery were stocked into an aerated 0.32-ha earthen pond at a density of 22,000 fish/ ha for 12 months, harvested, and restocked at 10,000 fish/ha for a further 2 years. The fish were fed a formulated diet containing 35% crude protein. No fish were mature at 1 year of age; at 2 years, most males (93%; total length, 304.0 mm, weight 412.7 g), but no females were mature; and at 3 years, most females (97%; 316.4 mm, 549.6 g) were mature. Three-year-old fish injected with 200 IU/kg human chorionic gonado-trophin spawned viable gametes. High fecundity (mean 139,286 eggs/ kg), fertilization rates (84.5%) and hatch rates (76.8%) demonstrate that broodfish can be domesticated and the life cycle of silver perch can be closed. The use of domesticated broodfish will eliminate reliance on wild populations and provide a basis for future hatchery production and selective breeding programs. 相似文献
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The oyster Crassostrea gigas (Thunberg 1793) is one of the most important species for shellfish aquaculture worldwide, and many cultivation activities rely on the use of spat produced in hatcheries. The operation of hatcheries and the efficiency of the processes involved remain largely unknown. We designed a protocol to evaluate 31 elements of the different phases of C. gigas spat production to identify critical aspects. Our survey was conducted in four hatcheries located in Mexico. The results showed that hatcheries operate with an overall fair control of processes. Nonetheless, six critical control items and six below-average control items suggest that some practices are inappropriate for producing high-quality spat. For 16 items, at least one hatchery applies a suitable production process, but only for three items all hatcheries use the best alternative. Major concerns are the few oysters used in spawning processes, the lack of controlled crosses either between them or with other oyster lines, and the current lack of genetic tests. Besides, broodstock pedigree is not documented and the genetic variability of spat is unknown. Additional concerns are that hatcheries have no controls in place for gamete production estimates or for fertilization, hatching, settlement, and survival rates. The protocol seemed adequate to identify the major difficulties faced by hatcheries. These findings set the basis for the improvement of production processes in hatcheries. Potential areas deserving further research are also underlined. 相似文献
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姜妍 《吉林农业科技学院学报》2013,(1):67-69
新闻报道是日常生活中常见的一种文体类型,就翻译而言,新闻报道有着不同于文学翻译的特殊性。归化和异化是文化翻译中常用的两大策略。从汉英新闻报道文化翻译的文本特点出发,研究归化和异化策略在汉英新闻报道翻译中的应用。 相似文献
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匍枝委陵菜引种驯化试验 总被引:4,自引:0,他引:4
匍枝委陵菜(Potentilla flagellaris Willd.ex Schlecht. ),又名蔓委陵菜、鸡头儿苗,为蔷薇科委陵菜属植物.分布于黑龙江、山东、山西、河北、甘肃、江苏,朝鲜、蒙古及俄罗斯西伯利亚地区也有分布.本文研究了野生地被植物匍枝委陵菜的生物学和生态学特性、物候特点、繁殖规律及开发利用价值.结果表明,匍枝委陵菜具有广泛的适应性和较强的抗逆性,生长快,繁殖力强,成坪时间短,绿期长,既可观叶又可观花,管理粗放,养护费用低,通过驯化和开发,可广泛应用于城市园林和绿化. 相似文献
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Understanding the historical development of indigenous systems will provide valuable information for the design of ecologically
desirable agroforestry production systems. Such studies have been relatively few, especially in Amazonia. The agroforestry
systems in Amazonia follow a trail that begins with the arrival of the first hunter-gatherers in prehistoric times, followed
by the domestication of plants for agriculture, the development of complex societies rich in material culture, the decimation
of these societies by European diseases, warfare, and slavery, the introduction of exotic species, and finally, the present-day
scenario of widespread deforestation, in which agroforestry is ascribed a potential role as an alternative land use. Despite
the upheavals which occurred in colonial times, greatly reducing the population of native tribes, a review of anthropological
and ethnobiological literature from recent decades indicates that a great variety of indigenous agroforestry practices still
exist, ranging from deliberate planting of trees in homegardens and fields to the management of volunteer seedlings of both
cultivated and wild species. These practices result in various configurations of agroforestry systems, such as homegardens,
tree/crop combinations in fields, orchards of mixed fruit trees, and enriched fallows. Together they constitute a stock of
knowledge developed over millenia, and represent technologies that evolved along with the domestication of native forest species
and their incorporation into food production systems. This knowledge is the basis for the principal agroforestry practice
employed by farmers in Amazonia today, the homegarden, and has potential to contribute to the development of other agroforestry
systems. 相似文献