An evaluation of the influence of stock origin and out-migration history on the disease susceptibility and survival of juvenile Chinook salmon

Various methods have been developed to mitigate the adverse effects of the Federal Columbia River Power System on juvenile Pacific salmon out-migrating through the Columbia River basin. In this study, we found that hatchery-reared spring Chinook salmon Oncorhynchus tshawytscha in the river are in varying degrees of health, which may affect delayed mortality and the assessment of the effectiveness of management actions to recover listed stocks (e.g., barging fish downstream versus leaving fish in the river). A laboratory disease challenge with Listonella anguillarum was completed on fish from Rapid River Hatchery and Dworshak National Fish Hatchery (NFH) with different out-migration histories: (1) transported by barge, (2) removed from the river before barging, or (3) left to travel in-river. Barged fish from Rapid River Hatchery experienced less mortality than fish from Dworshak NFH. No statistical differences were found between the hatcheries with fish that had in-river out-migration histories. We suggest that the stressors and low survival associated with out-migration through the hydropower system eliminated any differences that could have been present. However, 18-25% of the fish that were barged or collected before barging died in the laboratory before the disease challenge, compared with less than 2% of those that traveled in-river. Owing to disproportionate prechallenge mortality, the disease-challenged populations may have been biased; thus, they were also considered together with the prechallenge mortalities. The synthesis of prechallenge and disease-challenged mortalities and health characteristics evaluated during out-migration indicated that the benefit of barging was not consistent between the hatcheries. This finding agrees with adult survival and delayed mortality estimates for the individual hatcheries determined from adult returns. The results suggest that the health status of fish and their history before entering the hydropower system (hatchery of origin and out-migration path) are critical variables affecting the conclusions drawn from studies that evaluate mitigation strategies.     

Target-controlled infusion of propofol in dogs--evaluation of four targets for induction of anaesthesia

Four groups of 20 dogs were anaesthetised by means of target-controlled infusions of propofol designed to achieve 2.5 microg/ml, 3.0 microg/ml, 3.5 microg/ml or 4.0 microg/ml of propofol in blood. The dogs' pulse rate and respiratory rate were recorded before premedication and induction, immediately after endotracheal intubation and three and five minutes later (times 0, 3 and 5, respectively), and their arterial blood pressure was recorded oscillometrically just before induction and at times 0, 3 and 5. The targets of 2.5, 3.0, 3.5 and 4.0 microg/ml resulted in the successful induction of anaesthesia in 13 (65 per cent), 16 (80 per cent), 20 (100 per cent) and 20 (100 per cent) of the dogs, respectively. The incidence of postinduction apnoea was 0 (0 per cent), one (5 per cent), two (10 per cent) and eight (40 per cent) at time 5 for groups 2.5, 3.0, 3.5 and 4.0 mug/ml, respectively, and its incidence at time 5 was significantly higher in the 4.0 microg/ml group (P<0.05) than in the other groups. In all the groups there was a significant (P<0.05) decrease in blood pressure between just before induction and the later measurements. Although there were no statistically significant differences between the groups in terms of inducing anaesthesia at a specific target, a target of 3.5 microg/ml appears to ensure a successful induction of anaesthesia without a significant increase in the incidence of apnoea.     

世界银行倡导以农业促发展

当今世界的农业发展概况 当今世界的农业,广袤、多样且快速变化.如果地方层面、国家层面乃至全球层面都有健全的政策和支持性投入,今天的农业将为数以亿计的农村穷人摆脱贫困提供新的契机.农业向他们敞开脱贫道路包括家庭种植业和养殖业、高附加值的"新型农业"就业机会、新兴的农村非农产业创业和就业机会等等.     

种子的发芽和休眠(Ⅱ)

ABA不敏感突变型 vp1和 abi3在 ABA存在时也能发芽 ,这表明它们的野生型的相应基因产物参与了休眠的调控。因而 ,我们是否可以鉴别出这些由玉米 VP1和拟南芥菜 ABI3野生型的基因产物 ,从而解释为什么野生型种子对 ABA敏感而不能发芽 ?VP1和 ABI3这两个结构类似的基因编码某种蛋白 ,这个蛋白含有一个具有转录激活子特性的区段 (Mc Carty等 ,1991;Giraudat等 ,1992 )。它们不能在 vp1和 abi3突变体中合成 ,由此便产生了许多多效性效应 ,包括降低了一些种子成熟时期特有蛋白的合成 (如 Em蛋白、L EA蛋白 ;Paiva和 kriz,1994) ,降低…     

Effects of inbreeding on nodal root system morphology and architecture of white clover (<Emphasis Type="Italic">Trifolium repens</Emphasis> L.)

Plants of white clover (Trifolium repens L.) cultivar Crau, a self-fertile Crau genotype, and nine generations of inbred progeny were raised in sand culture in a glasshouse experiment. Digital images of the root systems were made and root morphological characteristics were determined on all the plants. Root architectural parameters were measured on the Crau parent and the S₁, S₄, S₆, and S₉ inbred lines. The clover roots became shorter and thicker with inbreeding but the number of root tips per plant was unchanged. Root architecture (branching pattern) was largely unaffected by inbreeding. It is concluded that inbreeding white clover will lead to shorter, thicker roots, and reduced nutrient uptake efficiency compared with the parent clover. The degree to which these deleterious traits are overcome during the development of F₁ hybrids needs to be determined.