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Four different‐sized (390±3, 140±2, 40±2, 16±1 g) Nile tilapia, Oreochromis niloticus (L.), stocked at the same biomass in timed pulse feeding chambers were provided 27–29°C water dominated by Microcystis (82%) and Scenedesmus (18%) to determine the effect of fish size on filtration rates. The number of Microcystis and Scenedesmus units filtered from the water decreased significantly with increasing tilapia size. The shaping constants and maximum filtration rates for Ivlev's feeding model used to describe the relation between filtration rates and the suspended particulate organic carbon (POC) concentrations were significantly different among the four sizes. Filtration rates of 763, 671, 512 and 300 mg C kg?1 h?1, which correspond to 70%, 82%, 86% and 90% saturation levels, were achieved at POC levels of 30, 32, 32 and 33 mg C L?1 for 16, 40, 140 and 390 g Nile tilapia respectively. Smaller tilapia achieved these rates at lower POC concentrations than larger tilapia. 相似文献
13.
Models describing the food uptake kinetics of a growing Artemia culture and the hatching rate of Artemia cysts are combined to yield equations capable of predicting the effects of variable algal cell concentration upon the growth rates of brine shrimp cohorts. The model illustrates that the feeding ability of the brine shrimp can be viewed as one becoming increasingly more efficient as the animals mature. This increasing efficiency in a population of variable age animals (from a single hatch) results in accelerated growth of first hatched animals relative to later hatched animals, especially at algal cell concentrations below certain threshold values. Growth rates of variable age groups of brine shrimp are mathematically manipulated to predict variable size brine shrimp at low algal cell concentration and uniformly sized brine shrimp at high algal cell concentration. This predicted result is confirmed with data from Artemia growth trials at high and low algal cell concentrations. It is suggested that similar variations in population attributes of other species may be explained as an animal-food interaction in which minor initial variations in individual animal maturity (weight, size, etc.) are magnified as a consequence of continuous competition for a common pool of food. 相似文献
14.
D.E. Brune 《Aquacultural Engineering》1982,1(1):63-70
An automatic self-cleansing high density brine shrimp reactor has been designed and tested, and the concept appears successful. Initial experiments suggest that extra-ordinarily high densities of brine shrimp may be maintained in such a system. The concept of a flowing film of glass beads appears to be a very useful technique in scouring waste material from animal culture tanks. The concept is particularly useful for culture of small marine herbivores in continuous culture. The bead flow rapidly removes waste material while allowing for water passage, yet completely containing the animals.Further design improvement and development should result in a high density brine shrimp culture system which is both simple and inexpensive to build, as well as reliable and cost effective to operate, and capable of efficient algal cell removal from culture water. 相似文献
15.
Di Carlo P Brune WH Martinez M Harder H Lesher R Ren X Thornberry T Carroll MA Young V Shepson PB Riemer D Apel E Campbell C 《Science (New York, N.Y.)》2004,304(5671):722-725
Forest emissions of biogenic volatile organic compounds (BVOCs), such as isoprene and other terpenes, play a role in the production of tropospheric ozone and aerosols. In a northern Michigan forest, the direct measurement of total OH reactivity, which is the inverse of the OH lifetime, was significantly greater than expected. The difference between measured and expected OH reactivity, called the missing OH reactivity, increased with temperature, as did emission rates for terpenes and other BVOCs. These measurements are consistent with the hypothesis that unknown reactive BVOCs, perhaps terpenes, provide the missing OH reactivity. 相似文献
16.
A commercial micropulverized 50% crude protein diet for penaeid culture was studied for biochemical oxygen demand and to assess its effect upon water quality in the hatchery and raceway environment. The feed was separated into 13 sizes ranging from 250 μm to 2 mm in diameter. The first order reaction rate constant (k) increased with decreasing particle size. The micropulverized feed was highly biologically reactive and the rate constant (k) varied from 0.1 to 0.24 day-1, depending on the particle size. The ultimate BOD was 660 mg/g. The goal of this research was to predict the impact of this feed in relation to varying particle size upon the oxygen and ammonia dynamics of the water. This information will enable shrimp hatchery managers to more effectively assess the water quality impact and water replacement schemes when using artificial micropulverized feeds. 相似文献
17.
Transformation and mineralization of 14C-labeled cellulose, peptidoglycan, and protein by the soil-feeding termite Cubitermes orthognathus 总被引：1，自引：0，他引：1
We performed feeding trials with the soil-feeding termite Cubitermes orthognathus using soil spiked by uniformly 14C-labeled preparations of cellulose, peptidoglycan, protein, and bacterial cells (Bacillus megaterium and Escherichia coli). When incubated in soil for 8 days in the absence of termites, cellulose and peptidoglycan showed low mineralization rates
(0.5% and 0.2%, respectively). However, when termites were present, their mineralization rates strongly increased (21.6% and
30.6%, respectively). The mineralization rate of protein was 12.4% in the control soils and increased to 36.2% in the presence
of termites. Mineralization of bacterial cells in control soils occurred in two phases (rapid mineralization during the first
4–5 days and stabilization thereafter). When termites were present, the rates of mineralization of bacterial cells increased
and the stabilization phase was abolished. In all cases, radiolabel accumulated in the termites and the solubility of the
labeled compounds located in the gut increased strongly. Mineralization was accompanied by transformation of residual carbon
from the humic acid fraction to the fulvic acid fraction during gut passage. High-performance gel permeation chromatography
demonstrated a strong shift in the size distribution of the residual carbon from high-molecular-weight towards low-molecular-weight
molecules in the gut of termites and an accumulation of small molecules in the termite bodies. The present study provides
strong evidence that structural polysaccharides of plants and bacteria and microbial biomass are carbon and energy sources
for soil-feeding termites.
Received: 29 May 2000 相似文献
18.
Human cytomegalovirus infects vascular tissues and has been associated with atherogenesis and coronary restenosis. Although established laboratory strains of human cytomegalovirus have lost the ability to grow on vascular endothelial cells, laboratory strains of murine cytomegalovirus retain this ability. With the use of a forward-genetic procedure involving random transposon mutagenesis and rapid phenotypic screening, we identified a murine cytomegalovirus gene governing endothelial cell tropism. This gene, M45, shares sequence homology to ribonucleotide reductase genes. Endothelial cells infected with M45-mutant viruses rapidly undergo apoptosis, suggesting that a viral strategy to evade destruction by cellular apoptosis is indispensable for viral growth in endothelial cells. 相似文献
19.
Brune WH Anderson JG Toohey DW Fahey DW Kawa SR Jones RL McKenna DS Poole LR 《Science (New York, N.Y.)》1991,252(5010):1260-1266
The nature of the Arctic polar stratosphere is observed to be similar in many respects to that of the Antarctic polar stratosphere, where an ozone hole has been identified. Most of the available chlorine (HCl and ClONO(2)) was converted by reactions on polar stratospheric clouds to reactive ClO and Cl(2)O(2) throughout the Arctic polar vortex before midwinter. Reactive nitrogen was converted to HNO(3), and some, with spatial inhomogeneity, fell out of the stratosphere. These chemical changes ensured characteristic ozone losses of 10 to 15% at altitudes inside the polar vortex where polar stratospheric clouds had occurred. These local losses can translate into 5 to 8% losses in the vertical column abundance of ozone. As the amount of stratospheric chlorine inevitably increases by 50% over the next two decades, ozone losses recognizable as an ozone hole may well appear. 相似文献
20.
Effect of soil invertebrates on the formation of humic substances under laboratory conditions 总被引：1，自引：0，他引：1
The complete polymerization of phenols and proteins (one of the processes involved in the formation of humic substances) was
explained. It was shown that fly (Bibio marci) larvae and earthworms (Aporrectodea caliginosa) participate in the complete polymerization of phenols and proteins. In a laboratory experiment, invertebrates participated
in the degradation of organic matter and the synthesis of humic substances, which was proved in experiments with 14C-labeled phenols and proteins. The same organic substances (phenols and proteins) without the impact of invertebrates were
used as the control substances. The distributions of the 14C isotope in alkaline extracts separated by solubility in acids (humic and fulvic acids) was compared to those of the control
substances. The portion of the 14C isotope in the humic acids in the excrements of Bibio marci was higher than that in the control substances. The content of 14C-labeled humic substances in the excrements of the earthworm Aporrectodea caliginosa exceeded the control values only in the experiment with proteins. When clay material was added to the organic substances,
the portion of the 14C isotope in the humic acids increased in both experiments with phenols and proteins. When these substrates passed through
the digestive tracts of the invertebrates, the polymerization of organic substances and the inclusion of proteins and phenols
into humic acids occurred. 相似文献