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

《Aquacultural Engineering》2020

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.  相似文献   

糖槭叶枯病发病规律及防治     

赵绥林  姜丽  褚继芳  吕庆茹  蔡纪文  陈建明 《中国森林病虫》2001,(Z1)

糖槭叶枯病 Phyllosticta negundinis病菌孢子放散开始期和高峰期与每年的温、湿度变化有关。病害发生严重程度与降雨量关系密切 ,降雨早且量大时病害严重。病菌以分生孢子器和分生孢子在病叶上越冬 ,通过气流传播成为翌年初侵染源。喷洒 70 %甲基托布津可湿性粉剂 10 0 0倍液和 75%百菌清可湿性粉剂 80 0倍液均能收到较好的效果  相似文献   

Effects of predator-induced visual and olfactory cues on 0+ perch (Perca fluviatilis L.) foraging behaviour     

V. N. Mikheev  J. Wanzenböck  A. F. Pasternak 《Ecology of Freshwater Fish》2006,15(2):111-117

Abstract –  Foraging juvenile fish with relatively high food demands are usually vulnerable to various aquatic and avian predators. To compromise between foraging and antipredator activity, they need exact and reliable information about current predation risk. Among direct predator-induced cues, visual and olfactory signals are considered to be most important. Food intake rates and prey-size selectivity of laboratory-reared, naive young-of-the-year (YOY) perch, Perca fluviatilis , were studied in experiments with Daphnia magna of two size classes: 2.8 and 1.3 mm as prey and northern pike, Esox lucius , as predator. Neither total intake rate nor prey-size selectivity was modified by predator kairomones alone (water from an aquarium with a pike was pumped into the test aquaria) under daylight conditions. Visual presentation of pike reduced total food intake by perch. This effect was significantly more pronounced (synergistic) when visual and olfactory cues were presented simultaneously to foraging perch. Moreover, the combination of cues caused a significant shift in prey-size selection, expressed as a reduced proportion of large prey in the diet. Our observations demonstrate that predator-induced olfactory cues alone are less important modifiers of the feeding behaviour of naive YOY perch than visual cues under daylight conditions. However, pike odour acts as a modulatory stimulus enhancing the effects of visual cues, which trigger an innate response in perch.  相似文献   

提高中锰白口铸铁韧性的研究     

李绪业  伍怡 《湖南农业大学学报(自然科学版)》1990,17(2)

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.  相似文献   

黑龙江省西部地区重瓣白玫瑰引种栽培及繁育技术     

李荣岐  李波  赵玉恒  阎敦梁 《防护林科技》2001,(3):21-22

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。  相似文献   

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

乔春贵  王庆钰  王玉兰  许耀奎 《吉林农业大学学报》1992,(1)

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。  相似文献   

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

K. R. Blanche‡  L. T. T. Tran-Nguyen  K. S. Gibb† 《Plant pathology》2003,52(4):505-512

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.  相似文献   

一次防治大豆灰斑病籽粒灰斑   总被引：1，自引：1，他引：0  

刘学敏  李利军 《东北农业大学学报》1996,27(3):231-234

通过室内及田间大豆不同生育期接种试验证明，籽粒感染灰斑病的关键时期是Ｒ３－Ｒ５期．Ｒ２期以前侵染不造成籽粒斑驳，据此提出一次防治大豆籽粒灰斑病的关键时期为Ｒ２－Ｒ４期．  相似文献   

Morphological characterization of the interaction between Diplocarpon rosae and various rose species     

O. Blechert  T. Debener † 《Plant pathology》2005,54(1):82-90

Blackspot, caused by Diplocarpon rosae , is the most severe and ubiquitous disease of garden roses, but information is lacking about genotype-specific forms of resistance and susceptibility of the host. Macro- and microscopic analyses of 34 rose genotypes with a defined monoconidial culture black spot inoculum identified susceptible and resistant rose genotypes and further genotype-specific subdivisions, indicating the presence of partial forms of resistance and different resistance mechanisms. In total, eight interaction types were characterized, five representing compatible (types 1–5) and three representing incompatible interactions (types 6–8). The incompatible interactions were characterized by the lack of any visible fungal structures beneath the cuticle (type 8), single-cell necroses (type 7) or necroses of larger cell clusters (type 6), the latter two types with penetration hyphae and haustoria in epidermal cells.  相似文献   

Pelargonium flower-break and pelargonium line pattern viruses in the Netherlands; purification,antiserum preparation,serological identification,and detection in pelargonium by ELISA     

I. Bouwen  D. Z. Maat 《European journal of plant pathology / European Foundation for Plant Pathology》1992,98(2):141-156

Two viruses, detected frequently in the Netherlands in pelargonium, were identified by serology and test plant reactions. Antisera were prepared and an ELISA procedure was developed to detect the viruses in pelargonium.One of the viruses, PFBV-N, proved to be pelargonium flower-break virus. With the antiserum to PFBV-N, it could be detected reliably throughout the year inPelargonium zonale Springtime Irene.The other virus, PLPV-N, was serologically closely related to pelargonium line pattern virus (PLPV) and to pelargonium ring pattern virus (PRPV), as were an old virus isolate from Saturnus, collected in the Netherlands in 1971 (L128), and PLPV isolates from Yugoslavia (PLPV-Y) and Denmark (PLPV-D). There were only minor differences in host-plant reactions between the virus isolates. Based on these tests, PLPV and PRPV are considered as isolates of the same virus, for which, for practical reasons, the name pelargonium line pattern virus is proposed.PLPV could be reliably detected by ELISA inP. zonale Springtime Irene and Amanda throughout the year with only a few exceptions. InPelargonium peltatum Tavira, however, reslts were erratic due to uneven distribution of virus in the plant. Best results were obtained when petioles of fully expanded leaves were tested.  相似文献