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.     

Acoustic evaluation of the vertical distribution of dwarf ayu Plecoglossus altivelis altivelis in Lake Biwa

SUMMARY: The vertical distribution of dwarf ayu Plecoglossus altivelis altivelis in the pelagic waters of Lake Biwa was evaluated from June to September in 1995–97 from eight acoustic surveys using a quantitative echosounder. In each survey, echoes from a depth range of 3 m to the sea bottom were collected at a station every 2.7 s for 24 h together with measurements of vertical profiles of water temperature and chlorophyll-a. The ayu's echoes were identified using an underwater video camera. The ayu were observed near the maximum chlorophyll-a depth and above the thermocline. Their density was highest at depths of 4–11 m with 2–4 individuals/m ³ and was almost zero below 20 m. Echo signs were recorded as having a frequent duration of more than 1 h at night, whereas were of a shorter duration in the day. The fish stay in the epilimnion during the day without any clear vertical migration, but are distributed more uniformly at night. The advantages of remaining in the epilimnion are discussed in terms of food availability and predator avoidance.     

国内高架桥绿化及研究现状

从高架桥区的生态环境、适生种类的选择以及高架桥绿化的养护管理、景观配置模式四个方面对国内的高架桥绿化及研究现状进行了分析和探讨,指出了存在的问题和解决方法,并对高架桥绿化的前景进行了展望.     

Multi-sectoral Participatory Urban Forestry Development in Philippines Metropolitan Manila

The Luntiang Kamaynilaan Project (Metro ManilaGreening Project) launched in 1988 planted trees inmajor thoroughfares, center islands, school premisesand other idle public lands, was basically a governmenteffort. When the funds ran out, the project also fizzledout. In both projects however, it is evident that the keyfactor is peoples participation.Gaining lessons from the past two projects, thegovernment established a collaborative effort ofgovernment and non-government organizations. TheCl…     

宿根花卉的特点及其在园林中的配置

根据宿根花卉种类繁多、色彩丰富、生长稳定、抗逆性强的特点,其在园林中的配置,宜于建花坛、花境,也可群植,与背景树相结合,还可作地被植物代替草坪,也可建单类花卉园.     

论韶关地区道路绿化植物的科学选择与配置

韶关地区道路绿化树种大多数是从南部珠三角地区和北部湖南地区引进，可能存在所引进树种是否适应韶关气候的问题。因此，如何运用科学的方法选择与配置道路绿化植物和确定合适的种植位置就成为道路绿化工程的关键。     

立式无筛饲料超微粉碎机的研发及质量检测分析

介绍了我国立式无筛饲料超微粉碎机的发展,简述立式无筛饲料超微粉碎机的组成、工作原理和优越性,分析质量检测及立式无筛饲料超微粉碎机技术的发展,展望制定行业标准的预期效果。     

The utilisation potential of urban greening waste: Tartu case study

In light of climate change and the increasingly limited availability of energy resources, any form of renewable raw materials that can be used for energy production should be accounted for. One of the most promising renewable sources is considered to be that of lignocellulosic feedstock. In urban forestry and greening, millions of tons of lignocellulosic waste is produced every year but that biomass mostly goes unused. The aim of this research project was to investigate the utilisation potential of this very form of waste biomass using a medium-sized town as a sample for the work (Tartu in Estonia, with a population circa 100,000). Woody and non-woody vegetation representing greening waste from different seasons was investigated: spring and autumn leaves, and mixed waste from urban greening which contained grass, twigs, and leaves. BMP assays were conducted to estimate the biogas production potential and the three step bio-ethanol production process was used to estimate the bio-ethanol production potential. In the bio-ethanol production process, an N₂ explosion pre-treatment was used, followed by enzymatic hydrolysis and fermentation. Map analysis was used to assess the area that was manageable by urban forestry and greening in the city of Tartu in order to estimate the amount of greening and forestry waste that was available for bioconversion and the volumes of biofuel that could be produced.     

Using suitability analysis to select and prioritize naturalization efforts in legacy cities: An example from Flint,Michigan

Given the lack of market demand and the abundance of vacant lots in legacy cities, not all vacant lands can be redeveloped or even maintained in a highly manicured state. While many vacant lots are being creatively reused as community gardens and side lots, in areas where residents are few and vacancy is high, the best use for vacant lands may be in a naturalized state such as meadows or forests. The author argues that in legacy cities, the critical question is not whether to naturalize (i.e. to stop mowing lots and allow for succession), but rather how to determine which properties to naturalize, in what order, and how. Using the example of Flint, Michigan, the author proposes suitability analysis as a method for selecting and prioritizing naturalization. Every property in the city of Flint was assigned a naturalization score derived by calculating subscores on nine variables, weighing the subscores by their importance, and summing. The nine variables included were contiguous vacant land, prospective vacancy, public ownership, land use designation, parks adjacency, proximity to industry, waterway buffers, property values, and population change. The naturalization scores can be combined with the results of a prior study to create a vacant land use decision tree pre- and post-demolition. Ultimately, the purpose of the paper is to facilitate property selection for naturalization while encouraging public discourse around what should happen with vacant lots in legacy cities.     

家庭绿化植物种类选择

通过对家庭居室不同空间特点的分析,根据家庭绿化的趋势,从绿化植物材料的适应性、观赏性、生态性和经济性方面探讨了家庭绿化材料的选择,以期为居室绿化提供参考依据。