The aquaculture potential of Tilapia rendalli in relation to its feeding habits and digestive capabilities     

《Physics and Chemistry of the Earth》2013

Tilapia rendalli is a predominately macrophagous fish. However, it was able to colonise an oligotrophic dam (Flag Boshielo) with limited macrophytes. Therefore, the diet of T. rendalli in this dam was investigated; its stomach contents were examined over 12 months. A size related dietary shift was evident. Juveniles fed mainly on zooplankton while sub-adult and adult fish grazed on both macrophytes and marginal vegetation. T. rendalli’s ability to strive in an environment with limited food resources led to a subsequent study to determine its aquaculture potential. Its growth performance was compared to that of the commonly cultured Oreochromis mossambicus. Juveniles of both species were fed a commercial tilapia diet for 60 days. Specific growth rate and protein efficiency ratio was comparable to that of O. mossambicus (P > 0.05, ANOVA). Feed conversion ratio was significantly higher (P < 0.05) in T. rendalli (1.43) than in O. mossambicus (1.25) indicating a better efficiency in feed utilisation by O. mossambicus. At a physiological level, protease, lipase and cellulase activities did not differ significantly between the two fish species (P > 0.05). Amylase activities were significantly higher (P < 0.05) in T. rendalli than in O. mossambicus. The highest amylase activities were recorded in the proximal intestines as 26.34 and 22.00 μmol/min/mg protein in T. rendalli and O. mossambicus respectively. This may be an indicator that T. rendalli is better equipped to digest plant diets. T. rendalli may be the aquaculture species of choice for emerging fish farmers who cannot afford the highly priced fishmeal as a protein source in fish diets.  相似文献   

Prediction of the consumption rates for juvenile Atlantic salmon (Salmo salar L.) on the scale of habitat patches: Development of empirical models based on stomach contents     

Frédéric Burton  Daniel Boisclair 《Limnologica》2013,43(5):332-338

Rivers and streams are unstable environments in which estimation of energetic costs and benefits of habitat utilization are the daunting exercise. Empirical models of food consumption may be used to estimate energetic benefits based on abiotic and biotic conditions in patches of habitat. We performed thirty daily surveys of fish stomach contents to estimate the consumption rates for juvenile Atlantic salmon (Salmo salar) in a river. The data were used to assess whether variations of daily consumption rates existed within the river, and to develop empirical models that could predict fish consumption rates using abiotic and biotic conditions as independent variables. Daily consumption rates based on stomach content surveys in the field (range: 0.15–1.49 g dry/(100 g wet day)) varied significantly depending on habitat patch (500–1000 m²), summer period, and sampling year. Variables such as water temperature, numerical density of salmon, water depth and moon phase explained 83–93% of the variations in daily food consumption rates. Daily consumption rates tended to increase with water temperature and depth, and were also higher near a full moon. However, they tended to decrease with the numerical density of salmon. Our work suggests that empirical models based on independent variables that are relatively simple to estimate in the field may be developed to predict fish consumption rates in different habitat patches in a river.  相似文献   

Nonmodal Growth on a Sphere at Various Horizontal Scales     

Richard Grotjahn  Cris Castello 《地球物理与天体物理流体动力学》2013,107(3):223-238

Nonmodal growth (NG) and unstable normal mode growth are considered in spherical geometry. Two groups of initial conditions (IC) are studied: "connected" IC (common in Cartesian studies) and "separated" IC (based on observed conditions prior to cyclogenesis). Time series of growth rates are emphasized in conjunction with eigenmode projections. Projections show that early on normal mode growth was much stronger for connected IC and that NG caused negative growth early on of some variables for separated IC. Projections explain why amplitude, kinetic energy (KE), and potential vorticity have more NG than available potential energy (APE). Though varying between ICs and with initial phase shift, NG increases with wavenumber. For middle wavelengths, NG is significant and positive using connected IC but negative or small using separated IC. Total energy and KE growth rates of short waves are very similar during the first 2 days for both ICs. Amplitude time series closely follow KE in all cases studied. APE has less overlap than does KE between the main modes present, so less NG occurs for APE than for KE. In separated IC cases, APE growth rates evolve consistent with emergence of an unstable normal mode and little NG.  相似文献   

Political Ecologies of Gentrification     

《Urban geography》2013,34(7):694-725

This article explores the possibilities for a political ecology of gentrification. Gentrification research, while firmly rooted in materialist social science, has not yet broadened its interests to consider ecological aspects of, or the role in gentrification of, discourses, social movements, and state policies of the environment. Understanding the political ecologies of gentrification involves recognizing the ways in which material relations and uneven resource consumption, concepts of nature, and the politics of urban environmental management affect gentrification processes. By synthesizing diverse literatures in urban studies, political ecology, urban environmental governance, consumption studies, and gentrification, this study argues that Vancouver, British Columbia represents a well-developed urban crucible for the new political ecologies of gentrification in North America. New developments in Vancouver increasingly contribute to gentrification using languages of sustainability and green consumption in a process of ecological gentrification.  相似文献   

西昆仑山前东段新生代褶皱冲断带及其锥形楔机制   总被引：2，自引：0，他引：2       下载免费PDF全文

梁瀚  杜治利  王宇  王易斌 《地质科学》2012,(3):808-823

西昆仑山前东段的和田-柯克亚构造带与塔里木盆地内的麻扎塔格构造带相距为200 km,两者近似平行,遥相对应,麻扎塔格构造带是和田-柯克亚构造带的前沿,山前挤压变形量沿古近系阿尔塔什组膏泥岩向北传递约200 km到麻扎塔格,形成往北东逆冲的断层传播褶皱,在盆地腹部表现为一条显著的北西向地形隆起。因此,整个西昆仑山前东段新生代褶皱冲断带宽约为270 km,长约为220 km,由和田-柯克亚构造带、麦盖提斜坡和麻扎塔格构造带组成。中部近200 km的麦盖提斜坡内没有明显构造变形,且整个褶皱冲断带的锥形楔角度远小于活动造山带的临界锥形角,说明古近系底部阿尔塔什组膏泥岩以及新生代沉积体的形态是这个褶皱冲断带锥形楔形成的主控原因,膏泥岩控制了锥形楔的顶面坡度α基底构造形态及上覆沉积楔形体则控制了锥形楔的底部滑脱层倾角β。  相似文献   

Growth, condition and energy stores of Arctic grayling fry inhabiting natural and artificial constructed Arctic tundra streams     

Kimberlea L.F. DriedgerLynn P. Weber  Ian K. BirtwellDavid M. Janz 《Limnologica》2011,41(1):63-69

Juvenile north-temperate and Arctic fishes are faced with trade-offs between energy allocation to growth and energy storage (primarily lipids) prior to over-wintering. We determined classical morphometric (fork length, body weight and condition factor) and biochemical (whole body triglycerides, muscle RNA/DNA ratio, muscle proteins) measures of growth and condition in individual young-of-the-year (YOY) Arctic grayling (Thymallus arcticus). Grayling were collected just prior to over-wintering in late August (approximately 50 days after swim-up) from two natural streams and five locations within a 3.4 km long artificial stream constructed as a fish habitat compensation project and diversion channel for the diamond mining industry in Northwest Territories, Canada (64°45′N). Fork lengths, body weights and whole body triglyceride levels in grayling collected from all sites along the artificial stream were significantly lower than fish collected from one of the natural streams. Condition factor (weight-at-length) was not different among grayling collected from natural and artificial streams. Muscle proteins were lower in grayling collected from four sites along the artificial stream compared to the natural streams. In contrast, muscle RNA/DNA ratios were greater in grayling collected from two sites in the artificial stream compared to natural streams. There were no consistent differences in any variable among grayling collected at the five artificial stream sites or among grayling collected from the two natural streams. The higher RNA/DNA ratios and lower fork lengths, whole body triglycerides and muscle proteins in grayling inhabiting the artificial stream are consistent with energy still being primarily allocated to growth in these fish at this late stage of summer. Individuals that are both larger and possess greater energy storage in the form of triglycerides are more likely to survive the long over-wintering period at this latitude. Our results suggest that YOY grayling using the artificial stream as nursery habitat will likely face increased over-winter mortality, thus raising concerns over the use of fish presence, spawning and rearing as criteria for the initial success of artificial streams as habitat compensation measures in Arctic tundra regions. Further research is needed to determine the potential consequences of reduced size and energy storage in juvenile fishes in order to assess the viability of stream fish habitat compensation and restoration projects associated with industrial development in Arctic tundra regions.  相似文献   

The impact of the herbicide atrazine on growth and photosynthesis of seagrass, Zostera marina (L.), seedlings     

Gao Y  Fang J  Zhang J  Ren L  Mao Y  Li B  Zhang M  Liu D  Du M 《Marine pollution bulletin》2011,62(8):1628-1631

The impact of the widely used herbicide atrazine on seedling growth and photosynthesis of eelgrass was determined. The long-term impact of the herbicide atrazine (1, 10 and 100 μg/L) on growth of eelgrass Zostera marina (L.) seedlings, maintained in outdoor aquaria, was monitored over 4 weeks. Exposure to 10 μg/L atrazine resulted in significantly lower plant fresh weight and total chlorophyll concentration and up to 86.67% mortality at the 100 μg/L concentration. Short-term photosynthetic stress on eelgrass seedlings was determined and compared with adult eelgrass using chlorophyll fluorescence. The effective quantum yield in eelgrass seedlings was significantly depressed at all atrazine concentrations (2, 4, 8, 16, 32 and 64 μg/L) even within 2 h and remained at a lower level than for adult plants for each concentration. These results indicate that atrazine presents a potential threat to seagrass seedling functioning and that the impact is much higher than for adult plants.  相似文献   

武都汉林沟流域古滑坡年龄的14C厘定   总被引：2，自引：1，他引：1  

吴玮江  叶伟林  孟兴民  王宗礼 《地球科学进展》2011,26(12):1276-1281

古滑坡一般是指全新世以前地质历史时期发生的滑坡。武都汉林沟流域发育有第四纪晚更新世以来不同时期的滑坡,具有规模大、数量多的特点,为武都白龙江中游滑坡发育历史研究提供了典型实例。通过滑坡体的形貌、结构特征、与其他地层的接触关系分析,确定古滑坡的存在。同时也发现古滑坡曾堵塞汉林沟形成堰塞湖,并压埋了许多古树木,古滑体中残留...  相似文献   

短期饥饿胁迫下（鱼免）鱼（Miichthys miiuy）早期生活阶段的生长及消化酶活性研究          下载免费PDF全文

单秀娟  窦硕增 《海洋与湖沼》2011,42(2):213-220

采用实验生态学方法,研究了饥饿胁迫对（鱼免）鱼（1—7日龄前期仔鱼,26—35日龄后期仔鱼,42—53日龄稚鱼）的生长、存活及消化酶（淀粉酶、脂肪酶、胰蛋白酶）活性的变化。结果表明,短期饥饿（2天）会显著降低前期仔鱼生长及消化酶活性;在后期仔鱼和稚鱼中,产生这种影响的饥饿时间分别为饥饿后3和6天,表明（鱼免）鱼仔、稚鱼...  相似文献   

饲料中不同蛋白质和脂肪水平对克氏螯虾（Procambarusclarkii）生长性能、体组成和消化酶活性的影响   总被引：3，自引：0，他引：3  

徐维娜  刘文斌  沈美芳  王莹  朱杰  徐刚  程龙 《海洋与湖沼》2011,42(4):521-529

采用3×3因子方法,进行了饲料中不同蛋白质和脂肪水平对克氏螯虾f均重（7．03±0．05）g]生长性能、体组成和消化酶活性的影响研究。试验设3个蛋白质水平（24％、27％和30％1和3个脂肪水平（4％、7％和10％）,共9组,每组4个重复,每个重复10尾虾,为期8周。结果表明,蛋白质和脂肪水平对成活率无显著影响（P〉0...  相似文献