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991.
Effects of seasonal and environmental changes on aquaculture production in tropical Lake Volta,Ghana
Emmanuel T. D. Mensah Hederick R. Dankwa Lauridsen L. Torben Ruby Asmah Benjamin B. Campion Regina Edziyie 《Aquaculture International》2018,26(6):1387-1400
Globally, aquaculture production is faced with numerous challenges, notable among which is water quality. The study determined seasonal environmental changes in Lake Volta and its implications on cage production of Nile tilapia, Oreochromis niloticus in experimental and commercial farm (Sun Woo Farm) set-ups. For each set-up, three cages were used, each measuring 81 and 162.5 m3 for experimental and commercial, respectively. The cages were stocked with 22.5 g fingerlings at a rate of 40 and 80 m?3 in experimental and commercial cages, respectively, and fed commercial diet. The growth performance, yield, economics, and selected water quality parameters were monitored during the dry and wet seasons between November 2014 and July 2015. There were no differences in water quality parameters between dry and wet seasons (p?>?0.05). Water quality for both seasons remained within limits required for good Tilapia growth in both set-ups. There were minimal variations in growth characteristics between seasons which were not significant; however, final mean weight and yields were high in the dry seasons in both set-ups. The cost of feed and fingerling accounting for about 80% of total costs were the major components identified to affect cost of production. A higher profit index and returns on investment were observed in the dry season in both set-ups and was linked to higher survival rates in the season. Production of Nile tilapia in cages can be cultured throughout the year without any adverse effects as exhibited in similar production patterns in both experimental and commercial set-ups. 相似文献
992.
Wim Verbeke Isabelle Sioen Karen Brunsø Stefaan De Henauw John Van Camp 《Aquaculture International》2007,15(2):121-136
The increasing number of marketable fish being supplied from aquaculture is a response to the increasing demand for healthy
food and is filling the gap left by depleting natural fish stocks. Little is known about the awareness and perception of the
consumer in terms of farmed fish versus fish from capture fisheries. The consumer's subjective point of view is of overriding
importance for the production system and product acceptance as well as for future market success. In this paper consumer perception
in Belgium is explored and compared against scientific evidence of farmed versus wild fish. Primary data were collected through
a consumer survey (April 2003) and focus group discussions (May 2004) with Belgian consumers. The majority of the consumer
sample reported no perceived differences between farmed versus wild fish. However, mean perception scores were slightly in
favour of wild fish on the attributes taste, health and nutritious value, in particular among consumers aged 55 years and
older. The availability of farmed fish was perceived to be better than that of wild fish, while the consumer's perception
of safety did not differ between farmed and wild fish. The focus group discussions indicated that consumers’ opinions and
beliefs about farmed fish are mainly based on emotion and image transfer from intensive terrestrial livestock production rather
than on awareness and factual knowledge of aquaculture.
相似文献
John Van CampEmail: |
993.
In contrast to schooling behavior in fish, which is well documented, the schooling behavior of an evolutionary counterpart,
squid, has not been adequately described in the literature. In the current study, we investigated the ontogeny of schooling
behavior in the oval squid Sepioteuthis lessoniana reared from hatching to about two months of age. During the two months of development, the distance and angle between nearest-neighbor
individuals decreased from 5.3 mantle lengths (ML) to 1.8 ML and from 42.7° to 24.2°, respectively. In addition, the swimming
distance of individuals in experimental duration decreased from 530.4 to 79.9 ML, and the relative swimming speed also decreased
from 17.1 to 4.6 ML/s during the same period, with increasing synchronized hovering of individuals. These observations clearly
suggest that oval squid swim randomly until 20 days after hatching, then form a school 30–60 days after hatching with an inter-individual
distance of 2.0 ML. At two months after hatching, oval squid individuals swam in a parallel orientation and formed a belt-shaped
arrangement, similar to the adult schooling behavior observed in natural populations. 相似文献
994.
Evaluating the durability of wood-based panels using internal bond strength results from accelerated aging treatments 总被引:1,自引:0,他引:1
In this study, the durability of wood-based panels was evaluated by comparing the internal bond (IB) strength retention after
five different laboratory-based accelerated aging tests with the IB retention after 5 years of outdoor exposure in Shizuoka
City. In each accelerated aging test, the IB retention of MDI-bonded panels showed high retention compared to other panels.
Outdoor exposure in Shizuoka City resulted in an IB retention value for particleboard (PF) and oriented strandboard (aspen)
of less than 10% after the 5-year exposure period. Medium-density fiberboards maintained their initial IB strength over the
same period. Calculation of the mean IB retention for all board types allowed comparison of the severity of aging between
the accelerated test methods and outdoor exposure. The ASTM six-cycle test method was the most severe among the standard treatment
cycles applied. 相似文献
995.
Anne Ganteaume Mercedes Guijarro Marielle Jappiot Carmen Hernando Corinne Lampin-Maillet Pedro Pérez-Gorostiaga José A. Vega 《Annals of Forest Science》2011,68(3):531-541
• Introduction
Wildfires are considered the most important disturbance in the Mediterranean Basin, and some are propagated over long distances due to lift-off and ignition of firebrands. 相似文献996.
Hyper-spectral remote sensing to monitor vegetation stress 总被引:1,自引:0,他引:1
Hong-Yan Ren Da-Fang Zhuang Jian-Jun Pan Xue-Zheng Shi Hong-Jie Wang 《Journal of Soils and Sediments》2008,8(5):323-326
Background, aim, and scope Vegetation stress diagnoses based on plant sampling and physiochemical analysis using traditional methods are commonly time-consuming,
destructive and expensive. The measurement of field spectral reflectance is one basis of airborne or spaceborne remote sensing
monitoring.
Materials and methods In this study, paddy plants were grown in the barrels evenly filled with 10.0 kg soil that was mixed respectively with 0,
2.5 × 207.2 and 5.0 × 207.2 mg Pb per 1,000 g soil. Rice canopy spectra were gathered by mobile hyper-spectral radiometer
(ASD FieldSpec Pro FR, USA). Meanwhile, canopy leaves in the field-of-view (FOV) of spectroradiometer were collected and then
prepared in the laboratory, (1) for chlorophyll measurement by Model 721 spectrophotometer, and (2) for Pb determination by
atomic absorption spectrophotometer (SpectraAA-220FS).
Results and discussion Canopy spectral reflectance in the region of visible-to-near-infrared light (VNIR) increased, because ascended Pb concentration
caused the decrease of canopy chlorophyll content. In the agro-ecosystem, however, heavy metal contamination is presented
typically as mixture and their interactions strongly affect actually occurring effects. Normalized spectral absorption depth
(D
n), and shifting distance (DS) of red edge position (REPs) revealed the differences in Pb concentration for canopy leaves,
especially at the early tillering stage. Due to insufficient biomass of rice plants, the 30th day was not reliable enough
for the selection of crucial growth stages. Some special sensitive bands might be omitted at the same time because of limited
sample sets.
Conclusions Our initial experiments are still too few in the amounts of both metals and plants neither to build accurate prediction models
nor to discuss the transformation from ground to air/spaceborne remote sensing. However, we are pleased to communicate that
ground remote sensing measurements would provide reliable information for the estimation of Pb concentration in rice plants
at the early tillering stage when proper features (such as DS and D
n) of reflectance spectra are applied.
Recommendations and perspectives Hyper-spectral remote sensing is a potential and promising technology for monitoring environmental stresses on agricultural
vegetation. Further ground remote sensing experiments are necessary to evaluate the possibility of hyper-spectral reflectance
spectroscopy in monitoring different kinds of metals’ stress on various plants. 相似文献
997.
Seok-In Yun Hee-Myong Ro Woo-Jung Choi Gwang-Hyun Han 《Journal of Soils and Sediments》2011,11(7):1253-1261
Purpose
Although nitrification plays a key role in the fate of soil nitrogen (N) under global warming, little information is available for the nitrifiers’ response to changing temperatures. Nitrogen isotope fractionation associated with nitrification can be a proxy of nitrifiers’ sensitivity to changing temperature. We hypothesized that the temperature-induced balance between the transport of substrate NH4+ into the microbial cell (supply) and the intracellular NH4+ oxidation (consumption) governs the intracellular NH4+ concentration and then affects nitrification rates and associated isotope fractionations. This study was conducted to understand the microbial response of NH4+ oxidation to changing temperatures by examining the effect of changing temperature on nitrification rate and apparent isotope fractionation. 相似文献998.
Adam C. Smith Nicola Koper Charles M. Francis Lenore Fahrig 《Landscape Ecology》2009,24(10):1271-1285
Estimating the relative importance of habitat loss and fragmentation is necessary to estimate the potential benefits of specific
management actions and to ensure that limited conservation resources are used efficiently. However, estimating relative effects
is complicated because the two processes are highly correlated. Previous studies have used a wide variety of statistical methods
to separate their effects and we speculated that the published results may have been influenced by the methods used. We used
simulations to determine whether, under identical conditions, the following 7 methods generate different estimates of relative
importance for realistically correlated landscape predictors: residual regression, model or variable selection, averaged coefficients
from all supported models, summed Akaike weights, classical variance partitioning, hierarchical variance partitioning, and
a multiple regression model with no adjustments for collinearity. We found that different methods generated different rankings
of the predictors and that some metrics were strongly biased. Residual regression and variance partitioning were highly biased
by correlations among predictors and the bias depended on the direction of a predictor’s effect (positive vs. negative). Our
results suggest that many efforts to deal with the correlation between amount and fragmentation may have done more harm than
good. If confounding effects are controlled and adequate thought is given to the ecological mechanisms behind modeled predictors,
then standardized partial regression coefficients are unbiased estimates of the relative importance of amount and fragmentation,
even when predictors are highly correlated. 相似文献
999.
Ingrid M. Malebane Jones Wilfred Ng’ambi David Norris Christian Mbajiorgu 《Tropical animal health and production》2010,42(8):1711-1718
Two experiments were carried out to determine the effect of dietary ascorbic acid supplementation levels on productivity,
carcass characteristics, and mortality of indigenous Venda chickens. The first experiment determined the effect of dietary
ascorbic acid supplementation levels on productivity and mortality rate of 175 unsexed Venda chickens between 1 and 6 weeks
old. The second experiment determined the effect of dietary ascorbic acid supplementation levels on productivity, carcass
characteristics, and mortality rate of 140 female Venda chickens between 8 and 13 weeks old. A completely randomized design
was used in both experiments. Supplementation of grower diets with ascorbic acid ranged from 0 to 2,000 mg per kg DM feed
in both experiments. Levels of ascorbic acid supplementation for optimum feed intake, feed conversion ratio, growth rate,
live weight, and breast meat yield were determined using a quadratic equation. The optimal dietary ascorbic acid supplementation
levels for feed conversion ratio, growth rate, and live weight of Venda chickens during the starter phase were 1,050, 1,301,
and 1,500 mg/kg DM feed, while, at the grower phase, the optimal supplementation levels for feed conversion ratio, growth
rate, live weight, and breast meat yield were 1,000, 1,250, 1,482, and 769 mg/kg DM feed, respectively. Results indicate that
different levels of ascorbic acid supplementation optimized feed conversion ratio, growth rate, and live weight of Venda chickens
at each growth phase. However, levels of ascorbic acid supplementation for optimum feed conversion ratio, growth rate, and
live weight were higher than that for breast meat yield. These findings have implications on ration formulation for Venda
chickens. 相似文献
1000.
Water relation parameters of bare-root seedlings of Chinese fir (Cunninghamia lanceolata Hook.)and Masson pine (Pinus massoniana Lamb.)were measured and changes of root growth potential as well as field survival rate of both species were studied after the bare-root seedlings were exposed in a sunny field condition.the results showed that masson pine had a lower osmotic potential(-2.07Mpa) at turgor loss point and at full turgor(-1.29Mpa),compared with Chinese fir(-1.80Mpa and -1.08Mpa respectively).The parameter Vp/Vo(63.27%) of Masson pine was higher than that of chinese fir (58.03%).This means that Masson pine has a stronger ability to tolerate desiccation,compared to Chinese fir according to analysis of above water relation parameters.Root growth potential and field survival rate decreased with prolonging duration of exposure.The field survival rate of both species was reduced to less than 40% after the seedling being exposed only two hours.Water potentials of -1.60 Mpa and -1.70 Mpa were suggested to be critical values for Chinese fir and Masson pine respectively in successful reforestation. 相似文献