The effects of density and artificial substrate on intensive shrimp Litopenaeus vannamei nursery production

Recirculating aquaculture systems (RAS) can be installed indoors, allowing year-round production of tropical animals in nearly any climate. A nursery phase is commonly used in Litopenaeus vannamei production since it allows for enhanced biosecurity and better quantification of animals while reducing space requirements. However, it is unclear whether animal density and inclusion of artificial substrate may improve shrimp performance during the nursery phase. In this experiment, we compared shrimp production parameters in two stocking densities with or without the use of an artificial substrate by creating four treatments: low-density LD; 1500 PL/m⁻³, low-density with substrate LDS, high-density HD; 3000 PL/m⁻³), and high-density with substrate (HDS). The LDS and HDS treatments included 0.46-m² of high-density polyethylene 2.5-cm mesh as a substrate, which increased the tank surface area by 21 %. Each treatment was randomly assigned to four 160-l culture tanks, each with a biofilter. The shrimp had an initial weight of 4 mg and were grown for 50 days. The low-density treatments had significantly higher dissolved oxygen (DO) and pH than the high-density treatments (P ≤ 0.001). Specifically, LDS had the highest DO and pH followed by the LD, HD, and HDS treatments, respectively. High-density treatments had significantly higher NO₂-N levels than low-density treatments during week 2 of the experiment when an unusually high concentration of nitrite was observed. FCR was significantly lower in both low-density treatments than in high-density treatments. At harvest, the total biomass (kg m⁻³) was significantly higher in high-density treatments than in low-density treatments (P ≤ 0.001), and the HDS treatment had a significantly greater biomass output than HD. Producers should consider artificial substrate and higher densities during nursery production to maximize shrimp production; however, the effects on water quality should also be taken into account.     

贵州农民财产性收入研究

阐述了财产性收入对提高贵州农民收入的重要性,深入分析了贵州农民财产性收入存在的问题和现状,并试图探索提高贵州农民的财产性收入的途径。     

西农萨能奶山羊血浆生长激素水平的变化及其与奶产量的关系

本实验用放免测定法(RIA)测定了38只西农萨能奶山羊(其中360～450日龄的青年羊10只,产前一月至产后90天的头胎和2胎羊各14只)血浆GH水平变化,分析了血浆GH水平与奶量的相关性。结果表明:360～450日龄的青年羊血浆GH维持在一个波动较小的范围(20.37±5.17～23.13±5.97ng/ml),头胎羊和二胎羊分娩前后及泌乳早期血浆GH水平的变化趋势相一致,在同一生理状态下,二胎羊血浆GH水平都显著地高于头胎羊。相关分析还表明:头胎羊和二胎羊血浆GH水平都与其奶量呈直线正相关关系(P<0.05)。综上结果可以认为,奶山羊血浆GN水平可作为选育高产奶山羊的一项指标。     

贵州自然分布山茶属植物的资源现状

介绍了贵州省原生山茶属植物的自然分布及资源现状，共46种4变种。     

提高中锰白口铸铁韧性的研究

为改善中锰白口铸铁的韧性以扩大其应用范围,本文探讨了C, Si, Mn等合金元素、变质处理和热处理工艺对中Mn白口铸铁组织和性能的影响.     

黑龙江省西部地区重瓣白玫瑰引种栽培及繁育技术

经在黑龙江省齐齐哈尔地区对重瓣白玫瑰引种栽培及繁育技术研究表明：该树种　１９９７～２０００年的平均抗寒指数为　２．７，冻害小于Ⅲ级，枝条冻伤长度小于　５０％，能正常开花，可以在此安家落户。同时对其形态特征、主要物候期、繁育技术和抚育管理作了介绍。     

向日葵[Helianthus annuus(L.)]白花粉突变体遗传研究初报

向日葵[IIelianlhus anuus (L.)]是我国的重要经济作物。其花粉通常呈深浅程度不同的黄颜色。据我们掌握和查新资料,目前世界上尚未见有关白花粉方面的报道。1989年7月下旬至8月上旬,我们在吉林农业大学向日葵育种试验田的恢复系C8711群体中,先后发现4株白花粉突变体。暂分别定名为C8711—1、C8711—2、C8711—3和C8711—4。在进行人工套袋之前,此4株突变体已经在一定程度上发生了开放授粉,其中C8711—4开放授粉程度较轻。成熟时单独收获这4株突变体的种子,以进行有关遗传学研究,本文拟对白花粉突变的遗传学机理进行初步的探讨。     

Detection, identification and significance of phytoplasmas in grasses in northern Australia

Sugarcane yields have been severely reduced by white leaf and grassy shoot phytoplasma diseases in many parts of Asia. Australian sugarcane crops are not known to be affected by these diseases, but plant pathogenic phytoplasmas found in other introduced and native grasses in northern Australia could pose a serious threat to the Australian sugarcane industry. To further evaluate this threat, leaves from plants of 20 grass species, with and without symptoms, were collected during field surveys in northern Australia and tested to determine whether phytoplasmas were present and whether symptoms were reliable indicators of phytoplasma presence. Molecular tools were used to detect and characterize phytoplasmas. Four different phytoplasmas were found in seven grass species known to grow near healthy sugarcane crops. All the phytoplasmas were closely related to sugarcane white leaf phytoplasma (SCWL), one of the phytoplasmas that causes disease in sugarcane in Asia. Four of the host plant species and two of the phytoplasmas were new records. The relationship between symptoms and phytoplasma presence was poor. Because some plants with symptoms tested negative for phytoplasmas, a series of surveys was carried out in which flowers, leaves, roots and stems of two known host plant species, Whiteochloa cymbiformis and Sorghum stipoideum, were tested separately on nine occasions during two wet seasons. This was done to investigate the distribution of phytoplasmas within plants over time. Results showed that spatial and temporal variation of phytoplasmas occurred in these two host plant species. Hence, evaluation of disease distribution within a region requires repeated testing of all plant parts from plants without symptoms, as well as those with symptoms. To date, there is no report of a vector capable of transmitting to Australian sugarcane the phytoplasmas found in grasses in this study. If one is present, or occurs in the future, then native and introduced grasses could constitute a large reservoir of phytoplasma for vectors to draw on. This work provides an early warning for the sugarcane industry that the potential for infection exists.     

贵州省退耕还林与农村经济发展研究

通过对贵州省贞丰、桐梓、锦屏等若干县市林业生态建设监理、检查、造林实绩核查等工作的实践和研究，认为退耕还林工程与农村经济发展相结合，目前应加强以下工作：选择林业主导产业；林产业时间、空间的合理布局；树种、林种的结构优化；林业体制创新；实施相关配套工程。     

Pathogenic mechanisms of caprine arthritis-encephalitis virus

Goats infected with caprine arthritis-encephalitis virus (CAEV) show chronic arthritis and cachexia, which are progressive in nature. The immunopathogenic mechanisms responsible for these progressive clinical symptoms have not been fully elucidated. Various haematological and immunological parameters were evaluated in experimentally-infected goats showing typical signs of CAEV-induced disease. Infected goats showed recurrent lymphocytosis that may be due to constant presentation of antigen by infected cells of a monocyte/macrophage lineage. The serum alkaline phosphatase and -glutamyl transferase concentrations were elevated in infected goats, a characteristic of hepatic and bone disorders. All other serum chemistry parameters were similar between infected and control goats. Importantly, the serum tumour necrosis factor- (TNF-) levels were higher in infected goats. The cachexia seen in infected goats may be at least partly due to altered metabolism as a result of prolonged elevation of serum TNF- levels. Depressed natural killer cell activity was observed in infected goats and may contribute towards the establishment of a persistent infection with CAEV.Abbreviations AIDS acquired immunodeficiency syndrome - CAEV caprine arthritis-encephalitis virus - GGT -glutamyl transferase - HBSS Hanks' balanced salt solution - HIV human immunodeficiency virus - NK natural killer - PBMC peripheral blood mononuclear cells - PCR polymerase chain reaction - SAP serum alkaline phosphatase - TNF tumour necrosis factor