共查询到20条相似文献，搜索用时 15 毫秒
1.
A major food web component in the orinoco river channel: evidence from planktivorous electric fishes
Deep-water sampling of the Orinoco River main channel resulted in the collection of an unexpectedly high abundance and diversity of specialized fishes. Twenty-eight of the more than 60 species collected belong to the Gymnotiformes(New World electric or knife fishes). One of the more numerous of these, a recently described species of the genus Rhabdolichops, consumes large numbers of very small planktonic Crustacea and insect larvae. These items are captured in the very swift, turbid, and deep waters of the Orinoco. Although the strong dependence of the river food web on terrestrial and floodplain food sources is well known, the specialized capabilities of Rhabdolichops and of other fishes that occur with it indicate a significant extension of the river food web into the main channel. 相似文献
2.
Andrea Giovanna NI&# O-SAVALA Zhong ZHUANG Xin MA Andreas FANGMEIER Huafen LI Aohan TANG Xuejun LIU 《农业科学与工程前沿(英文版)》2019,6(4):419
The application of mineral and organic phosphorus fertilizers to arable land has greatly increased crop yield to meet the world food demand. On the other hand, impurities in these fertilizers, such as heavy metals, are being added to agricultural soils, resulting both from the raw materials themselves and the processes used to obtain the final product. Cadmium, a non-essential and toxic heavy metal, has been found in relatively high amounts in common P fertilizers obtained from sediments. This metal poses a high risk for soil fertility, crop cultivation, and plants in general. Furthermore, human health might be compromised by the cadmium concentrations in agricultural and livestock products, due to the bioaccumulation effect in the food web. The accumulation in the different matrixes is the result of the high mobility and flexible availability of this harmful metal. This review summarizes risks to human health, the factors influencing cadmium movement in soils and crop uptake, as well as common plant responses to its toxicity. In addition, it summarizes cadmium balances in soils, trends, long-term experiments, and further studies. Cadmium inputs and outputs in arable soil, together with their calculated concentrations, are compared between two different regions: the European countries (in particular Germany) and China. The comparison appears useful because of the different proportions in the inputs and outputs of cadmium, and the diverse geographical, environmental and social factors. Moreover, these variables and their influences on cadmium contamination improve the understanding of the pollution from phosphate fertilizers and will help to establish future mitigation policies. 相似文献
3.
运用产出导向DEA模型,选取1990-2012年主粮生产中农用物资投入数据,对其投入效率进行评价。分析得出,23年的样本中主粮农资投入无效率的年份有16个,其中年投入效率值低于全部样本平均水平的年份有11个,且主要集中于1993-1998年和2005-2012年2个时间段。同时,无效率年份的规模效益均为递减,而综合技术效率多受规模效率较低拖累。这说明在当前资源配置和利用条件下,农资投入过大,产生了投入浪费。研究还显示主粮生产中农用物资投入呈现粗放式增长,多数年份存在资源配置不合理、规模效益不高、农资投入增长不协调等问题,其中农用物资要素之间的投入结构不协调问题相对突出。因此,适当放缓投入规模,将现有农资进行合理再分配对提升投入效率有所帮助。而长远来看,更需要对农资投入配置机制进行优化,积极调整生产要素的投入格局,把以农资投入规模增加带动主粮产量提升的粗放式增长模式转变为技术先进、资本密集、规模化的现代经营模式,才可持续有效提高农资投入效益,有助于主粮产量的进一步提高和增产潜力的提升。 相似文献
4.
Araujo-Lima CA Forsberg BR Victoria R Martinelli L 《Science (New York, N.Y.)》1986,234(4781):1256-1258
Detritivorous fishes form an important part of the ichthyomass in the Amazon basin. Most of these fishes are contained in the orders Characiformes and Siluriformes (catfishes). The Characiformes constitute more than 30% of the total fish yield in the Amazon basin, whereas the catfishes are of minor importance. Stable isotope data indicate that Characiformes species receive most of their carbon through food chains originating with phytoplankton, while the Siluriformes receive a significant part of their energy from other plant sources. 相似文献
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软刺裸鲤(Gymnocypris doubula)和齐口裂腹鱼(Schizothorax prenanti)分别是生长在高海拔(4 500 m)低氧的青藏高原水体和低海拔(1 000 m)长江上游水体的两种裂腹鱼亚科鱼类。为探究不同海拔裂腹鱼体内微量元素的差异,采用微波消解电感耦合等离子体质谱(ICP-MS)法测定软刺裸鲤(GD)和齐口裂腹鱼(SP)肌肉、脊椎骨和头盖骨中Na、Mg、Al、K、Ca、Fe、Zn等常量元素和V、Cr、Mn、As、Se、Sr、Sb、Ba等微量元素含量,并对两种裂腹鱼的元素含量进行差异比较和分析。结果表明,GD和SP肌肉中仅有Se和Sb含量呈现显著性差异,仅有As含量在两种裂腹鱼的脊椎骨中存在显著差异。GD肌肉中极高含量的Se和Sb元素、以及GD脊椎骨中极高含量的As元素可能与高原低氧适应相关。该研究在国内首次使用微波消解法对两种不同海拔高度的裂腹鱼肌肉和骨骼中的常量元素和微量元素进行测定分析,有效探究了两种裂腹鱼体内元素的差异,为后续通过体内组织的元素分析来解析裂腹鱼适应低氧环境的生理机制提供依据。 相似文献
6.
Agricultural performance in Tanzania under structural adjustment programs: Is it really so positive?
Bert Meertens 《Agriculture and Human Values》2000,17(4):333-346
The performances in the food and cashcrop sectors and the availability and consumption ofagricultural inputs in Tanzania during structuraladjustment programs (1986–1996) are compared withperiods prior to this IMF/World Bank backed reform.The positive developments in the first five years ofreform appear to be not sustainable. Presentlyproductivity levels per rural capita for importantfood and cash crops are declining. There are nofurther improvements in the availability andconsumption of agricultural inputs. The removal ofsubsidies on agricultural inputs from 1991 onwards iscrucial in explaining the decline in maize production,the main food crop in Tanzania. Some assumptionsbehind the reform measures are proving to be wrong.Modifications are thus needed to improve theagricultural sector of Tanzania in a sustainable way.Structural adjustment programs usually go too far inreducing the role of the government. However,government involvement might be necessary to ensure ahigher consumption of agricultural inputs and thus abetter performance of the agricultural sector inTanzania. A higher productivity in the agriculturalsector is needed in Tanzania to avoid food securityproblems in the future. 相似文献
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Probably in early 1967, a piscivore from South America, Cichla ocellaris, was introduced to Gatun Lake in the Panama Canal Zone. As this predator population spread through the lake, the initial effect was dramatic reductions in almost all secondary consumers. These species reductions produced, in turn, second- and third-order changes at other trophic levels of the ecosystem. The resulting changes in the lake community can be seen best by examining the general Gatun Lake food web. The decrease in numbers of the important planktivore Melaniris has resulted in changes within the zooplankton community, as illustrated by the cladoceran Ceriodaphnia. The tertiary-consumer populations, such as tarpon, black terns, kingfishers, and herons, formerly dependent on small fishes for food, appear less frequently in the Cichla areas of the lake. There has also been, possibly, a resurgence of the local mosquito populations (which are malaria vectors), caused by the reduction in the populations of insect-eating fishes. Even the primary producers may be affected by this introduction. Although at present the Gatun Lake ecosystem is undergoing rapid changes, we anticipate an eventual return to some form of equilibrium. However, it will be some time before we can evaluate the permanence or transience of the many changes produced in the trophic levels by the introduction of a single, top-level predator to this lake system. 相似文献
8.
类胡萝卜素(carotenoid)是影响鱼类体色特性的主要色素,但鱼类自身不能合成这一色素,因此必须从食物中摄入。鱼类类胡萝卜素着色过程涉及对类胡萝卜素的代谢与沉积过程,色素细胞的分化和空间排列,以及与其他色素和色素细胞间的相互作用,这一过程非常复杂,但我们对其机理知之甚少。综述了类胡萝卜素着色效果与鱼类遗传特性、生理状态以及环境因素之间的相关关系,对该研究领域发展趋势进行了讨论和展望,期望为我国研究鱼类体色的形成机制提供一些新的信息。 相似文献
9.
Toxaphene insecticide: a complex biodegradable mixture 总被引：1，自引：0，他引：1
J E Casida R L Holmstead S Khalifa J R Knox T Osawa K J Palmer R Y Wong 《Science (New York, N.Y.)》1974,183(124):520-521
Adsorption and gas-liquid chromatography separate toxaphene into at least 175 polychlorinated 10-carbon compounds including Cl(6), Cl(7), Cl(8), Cl(9), and Cl(10) derivatives. One toxic component is 2,2,5-endo,6-exo,8,9,10-heptachlorobornane. Rats metabolically dechlorinate toxaphene, removing about half of the chlorine from the technical insecticide and from each of seven subfractions of varying composition and toxicity. 相似文献
10.
太湖银鱼和主要鱼类渔获量间的相关分析 总被引：1，自引：0，他引：1
根据太湖1973-2002年连续30年的鱼类渔获量统计资料,研究了太湖银鱼和主要鱼类渔获量间的相关关系.并根据2004-2005年的食性调查初步结果对相互关系的机制进行了分析.简单相关分析表明,太湖银鱼和鲌鱼、鲢鳙鱼渔获量间的正相关关系均达到极显著水平;偏相关分析表明,太湖银鱼和鲌鱼渔获量间的正相关关系达到极显著水平,和其它鱼类渔获量间的正相关关系达到显著水平,和鲢鳙鱼渔获量间的正相关关系虽然没有达到显著水平,但有一致趋势;简单相关和偏相关分析均表明,太湖银鱼和和鲚鱼渔获量间的相关关系均没有达到显著水平.分析认为:太湖银鱼渔获量的变化除受捕捞强度及环境理化等因素影响外,鲌鱼通过捕食调节,可能降低了鲚鱼和银鱼的食物竞争强度,从而有利银鱼增加;鲢、鳙鱼通过和鲚鱼的食物竞争,从而间接促进了银鱼种群数量发展. 相似文献
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太湖鳜鱼摄食习性的研究 总被引：1，自引：0，他引：1
本文详细研究了太湖鳜鱼的食物组成，摄食习性与季节的关系，摄食习性与体长的关系等，并探讨了其在大湖渔业中的地位。研究结果表明，鳜鱼对大湖经济鱼类危害不大，并且能抑制野杂鱼的过度繁殖，因此提出了保护和增殖鳜鱼的主张。本研究还为鳜鱼的人工养殖在饵料选择问题上提供了一定的指导作用。 相似文献
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Rice, wheat and maize are the main staple food crops to ensure the food security in China with diversified climate condition, cropping system and environmental and socio-economic factors across provinces. Spatial variation of technical efficiency in farmers' field is helpful to understand the potential to improve farmers' yield given the inputs level and reduce the yield gap. The study is based on a large-scale farm household survey which covered 1 218 rice farmers, 3 566 wheat farmers and 2 111 maize farmers in the main producing areas. The results indicate that rice farmers are with very high technical efficiency level, nearly 0.9 on average, with little room to improve the efficiency of agricultural inputs. Similar results have been found in wheat and maize farmers' fields, although the technical efficiency levels are lower than that of rice farmers while still at a high level with obvious variation across regions. Farmers with higher yield level also achieve better technical efficiency in most locations. Both local environmental and socio-economic factors significantly affect farmers' technical efficiency. In the context of urbanization and economic development, improved and new agricultural technologies need to be prioritized and facilitated to improve cereal yield at farm level. 相似文献
13.
对黄花泡乌鳢（Ｏｐｈｉｏｃｅｐｈａｌｕｓ ａｒｇｕｓ）的食性进行了分析。结果表明：该鱼的仔鱼期主要以浮游的甲壳动物为食,另外也食少量的摇蚊幼虫;幼鱼期以水生昆虫的幼虫及小虾为食;成鱼期除食相当部分的虾以外,几乎全部是鱼类。乌鳢食谱范围较广泛,对水体中主养的经济鱼类构不成危害,建议应合理地开发利用乌鳢的种群资源。 相似文献
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用氢化物原子吸收法分析测定了鱼组织中汞和硒的含量，并对汞和硒之间的相关性进行了研究。结果表明，汞和硒在鱼样的肝脏和肌肉中的含量都存在显著性差异，且大多是肝脏中的含量大于肌肉中的含量。不同种类的鱼，营养级较高的鱼，其汞和硒富集能力强，含量较高。在汞含量较低的情况下，鱼组织中汞与硒的摩尔比值随汞含量的增加而增加。 相似文献
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[目的]探讨陕西省产地养殖鱼类重金属的含量水平、分布特征以及食用安全。[方法]以陕西省主要水产品养殖区的主要养殖品种为抽样监测对象,应用原子吸收和原子荧光分光光度法,分别测定陕西省陕南、关中、陕北7个地市随机采集的当地主要养殖水产品肌肉中锌(Zn)、铜(Cu)、汞(Hg)、砷(As)、镉(Cd)、铅(Pb)的含量。并依据食品中污染物限量国家标准和水产品中有毒有害物质限量标准分析重金属在陕西省养殖水产品中的分布特征和食用安全性。[结果]陕西省养殖水产品肌肉中重金属平均含量依次为ZnCuHgPbAsCd;其中Zn检出率最高,为100%,As检出率最低,为39.3%;Zn、Cu、As、Hg含量水平在不同食性养殖水产品中存在显著性差异,Pb和Cd含量水平无显著差异;陕西省不同地区养殖水产品As和Hg含量水平存在显著性差异,Zn、Cu、Pb、Cd含量水平无显著性差异。食用安全性评价表明,陕西省主要养殖水产品的重金属综合污染指数小于1.0,无污染;综合污染指数关中地区(0.154)陕南地区(0.085)陕北地区(0.061)。[结论]研究可为渔业管理部门了解水产品质量安全状况,开展渔业环境及水产品质量安全监管提供参考依据。 相似文献
16.
太湖沿岸区几种肉食性鱼类蛋白酶活性的研究 总被引：4，自引：0，他引：4
本文对太湖沿岸区几种常见肉食性鱼类的胃蛋白酶和胰蛋白酶活性进行了比较研究，发现它们的胃蛋白酶比活力有显著差异（Ｐ〈０．０１），其中，尤以底栖无脊椎动物食性的黄颡鱼最高，沙塘鳢次之，而以鱼、虾为食的乌鳢、鳜鱼的较低。但它们的胰蛋白酶比活力并无显著性差异（Ｐ〉０．１０）。作者认为，肉食性鱼类９特别是胃发达的）食物的消化主要集中在胃中，胃蛋白酶活性的高低与食物的硬度（钙质的含量）成正相关，而在小肠中，只 相似文献
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Agricultural development programs have so far been largely unable to meet the food needs of the world's poorest. Increased food production can be achieved only from more intensive agriculture, which requires greater energy inputs per farm worker. Problems of technological infrastructure and escalating oil prices appear to preclude the spread of mechanization to Third World agriculture at this time. Efficient utilization of grazing animals in specific integrated farming systems could not only increase energy inputs through draft and transportation but also increase the yield of high-grade products and by-products from the renewable energy of biomass. An approach to development based on animal agriculture systems is suggested that might initiate a self-sustaining, more productive agriculture requiring only small inputs of fossil-fuel energy. 相似文献
19.
[目的]进一步探讨油茶饼粕在淡水鱼虾蟹病害防治中的应用。[方法]采用单因子梯度法,利用不同浓度的油茶饼粕浸出液对5种有鳞鱼和2种无鳞鱼及青虾和螺蛳等水产动物进行毒性试验。[结果]油茶饼粕浸出液对有鳞鱼鲢、鳙、草鱼、鲤、鲫鱼24和48 h的LC50分别为6.25和5.16 mg/L、5.26和5.12 mg/L、9.74和5.87 mg/L、9.29和7.64 mg/L、11.3和7.55 mg/L;油茶饼粕浸出液对无鳞鱼斑点叉尾鮰、泥鳅在24和48 h的LC50分别为：7.47和5.00 mg/L、26.42和16.80 mg/L;青虾和螺蛳在90 mg/L油茶饼粕浸出液的情况下48 h存活率达100%。油茶饼粕浸出液对淡水鱼类具有显著的毒杀性,而淡水青虾和螺蛳对油茶饼粕浸出液具有较高的耐受性。[结论]利用油茶饼粕浸出液控制混入淡水虾蟹养殖池的野杂鱼和防治病害,具有较好的前景。 相似文献
20.
为了解洋山港航道疏浚对海洋鱼类早期阶段的影响,通过对工程海域3个取样点疏浚泥的取样分析,应用环境质量综合评价法和毒理学方法,评价了洋山港航道疏浚泥溶出液对鱼类胚胎、仔鱼的毒性效应。结果表明:工程海域疏浚泥溶出液质量存在较明显差异,以3号点疏浚泥溶出液质量相对最好,1号点次之,2号点最差。3个取样点疏浚泥溶出液对黑棘鲷胚胎孵化率的影响不明显,但对仔鱼具有明显毒性效应。在高浓度组,1号、2号和3号点黑棘鲷仔鱼48 h的死亡率分别为25.46%、29.81%和14.76%,大黄鱼仔鱼48 h的死亡率分别为20%、40%和20%;在次高浓度组,1号、2号和3号点黑棘鲷仔鱼48 h的死亡率分别为15.41%、22.38%和9.45%,大黄鱼仔鱼48 h的死亡率分别为20%、20%和15%。大黄鱼仔鱼的死亡率略大于黑棘鲷仔鱼。疏浚泥溶出液浓度与仔鱼死亡率之间具有显著正相关关系,2号点疏浚泥溶出液毒性最大,1号点次之,3号点最小。 相似文献