Construction of habitat suitability models (HSMs) for benthic macroinvertebrate and their applications to instream environmental flows: A case study in Xiangxi River of Three Gorges Reservior region, China

Based on a long-term ecological monitoring, the present study chose the most dominant benthic macroinvertebrate (Baetis spp.) as target organisms in Xiangxi River, built the habitat suitability models (HSMs) for water depth, current velocity and substrate, respectively, which is the first aquatic organisms model for habitat suitability in the Chinese Mainland with a long-term consecutive in situ measurement. In order to protect the biointegrity and function of the river ecosystem, the theory system of instream environmental flow should be categorized into three hierarchies, namely minimum required instream flow (hydrological level), minimum instream environmental flow (biospecies level), and optimum instream environmental flow (ecosystem level). These three hierarchies of instream environmental flow models were then constructed with the hydrological and weighted usable area (WUA) method. The results show that the minimum required instream flow of Xiangxi River calculated by the Tennant method (10% of the mean annual flow) was 0.615 m(3) s(-1); the minimum instream environmental flow accounted for 19.22% of the mean annual flow (namely 1.182 m(3) s(-1)), which was the damaged river channel. ow in the dry season; and 42.91% of the mean annual flow (namely 2.639 m(3) s(-1)) should be viewed as the optimum instream environmental flow in order to protect the health of the river ecosystem, maintain the instream biodiversity, and reduce the impact of small hydropower stations nearby the Xiangxi River. We recommend that the hydrological and biological methods can help establish better instream environmental. ow models and design best management practices for use in the small hydropower station project. (C) 2008 National Natural Science Foundation of China and Chinese Academy of Sciences. Published by Elsevier Limited and Science in China Press. All rights reserved.

Sequential ultrastructural and biochemical changes induced in vivo by the hepatotoxic microcystins in liver of the phytoplanktivorous silver carp Hypophthalmichthys molitrix

Up to now, in vivo studies on the toxic effects of microcystins (MCs) on the ultrastructures of fish liver have been very limited. The phytoplanktivorous silver carp was injected i.p. with extracted hepatotoxic microcystins (mainly MC-RR and -LR) at a dose of 1000 mu g MC-LReq. kg(-1) body weight, showing a time-dependent ultrastructural change in liver as well as significant increases in enzyme activity of plasma alanine aminotransferase (ALT), aspartate aminotransferase (AST) and lactate dehydrogenase (LDH). We observed for the first time the occurrence of a large amount of activated secondary lysosomes, which might be an adaptive mechanism to eliminate or lessen cell damage caused by MCs through lysosome activation. Quantitative and qualitative determinations of MCs in the liver were conducted by HPLC and LC-MS2, respectively. MCs concentration in the liver reached the maximum (114.20 mu g g(-1) dry weight) after 3 h post-injection, and then rapidly dropped to 7.57 mu g g(-1) dry weight at 48 h, indicating a deputation of 99% accumulated MC-LReq. On the other hand, a decrease trend in glutathione (GSH) concentration was observed in the liver of silver carp while the activity of glutathione S-transferase (GST) increased significantly after injection. The high tolerance of silver carp to MCs might be due to the high basic GSH level in their liver, and/or an increased GSH synthesis. (C) 2007 Elsevier Inc. All rights reserved.

Molecular cloning of growth hormone receptor (GHR) from common carp (Cyprinus carpio L.) and identification of its two forms of mRNA transcripts

The cDNA of growth hormone receptor (GHR) was cloned from the liver of 2-year common carp (Cyprinus carpio L.) by reverse transcription-polymerase chain reaction (RT-PCR) and rapid amplification of cDNA end (RACE). Its open reading frame (ORF) of 1806 nucleotides is translated into a putative peptide of 602 amino acids, including an extracellular ligand-binding domain of 244 amino acids (aa), a single transmembrane domain of 24 aa and an intracellular signal-transduction domain of 334 aa. Sequence analysis indicated that common carp GHR is highly homologous to goldfish (Carassius auratus) GHR at both gene and protein levels. Using a pair of gene-specific primers, a GHR fragment was amplified from the cDNA of 2-year common carp, a 224 bp product was identified in liver and a 321 bp product in other tissues. The sequencing of the products and the partial genomic DNA indicated that the difference in product size was the result of a 97 bp intron that alternatively spliced. In addition, the 321 bp fragment could be amplified from all the tissues of 4-month common carp including liver, demonstrating the occurrence of the alternative splicing of this intron during the development of common carp. Moreover, a semi-quantitative RT-PCR was performed to analyze the expression level of GHR in tissues of 2-year common carp and 4-month common carp. The result revealed that in the tissues of gill, thymus and brain, the expression level of GHR in 2-year common carp was significantly tower than that of 4-month common carp.

Distribution of phytoplankton in the Three-Gorge Reservoir during rainy and dry seasons

After damming of the Yangtze River, in order to explore the impacts of the Three-Gorge Dam (TGD) on the aquatic ecosystem, phytoplankton composition, abundance and biomass spatial distribution were studied in the Three-Gorge Reservoir (TGR), and the closest upstream anabranch Xiangxi River, which is 38 kin away from the Three-Gorge Dam (TGD) during August (rainy season) 2004 and April (dry season) 2005. In surveys, 6 transects (2 downstream and 4 cross-stream) and 25 stations have been investigated and 314 samples were collected from the surface to the river bed with water samplers. In TGR, 63 taxa and 60 taxa were identified in the rainy and dry seasons, respectively. In the Xiangxi River, 39 taxa were observed in the rainy and dry seasons. Algal blooms occurred in the Xiangxi River and at the influx region of the Yangtze and Xiangxi in both seasons, but had not occurred prior to damming. In the rainy season, the dominant species was Chroomonas acuta with 1.84 x 10(7) cells l(-1), and in the dry season the dominant species were Asterionella formosa and Cryptomonas ovata with 1.34 x 10(7) cells l(-1) and 1.79 x 10(6) cells(.)l(-1), respectively. In the main channel of TGR, there were no significant correlations between phytoplankton abundance and the concentrations of the main soluble nutrients. In the Xiangxi River, significant negative correlations were observed between phytoplankton abundance and nitrate (Spearman, p < 0.01, n=21), phosphate (Spearman, p < 0.05, n=21) and silicate (Spearman, p < 0.01, n=21) in the rainy season, and similar correlations were also observed with nitrate (Spearman, p < 0.05, n=28) and silicate (Speannan, p < 0.01, n=28), but not with phosphate in the dry season. Since the damming of the Yangtze River, eutrophication in the anabranch within the backwater has occurred and become severe, and the frequency of algal bloom within TGR and anabranches is expected to increase. (c) 2006 Elsevier B.V. All rights reserved.

Population genetic structure of an endemic cyprinid fish, Ancherythroculter nigrocauda, in the upper reaches of the Yangtze River and its implication for conservation

Ancherythroculter nigrocauda is a cyprinid fish endemic to the upper reaches of the Yangtze River, which has been reported to have 2 or 3 chambers to its air bladder. Morphological studies showed no differences between individuals with different types of air bladder, but did demonstrate geographical differences from different sources. After the completion of the Three Gorges Dam, it was expected that the population of this species would decrease, but artificial breeding and stocking is under consideration to protect this species from extinction. In the present study, mtDNA cytochrome b gene sequences were determined and analyzed for A. nigrocauda samples of different morphotypes and sources to identify their genetic differentiations, and thereby guide plans for the artificial propagation and conservation of this species. Haplotype diversity index values (h) and nucleotide diversity values (pi) for all the populations were found to be high indicating their high level genetic diversity. An analysis of molecular variance identified no differentiation among the studied populations. Therefore, we suggested that the individuals of different morphological types and geographical sources belong to the same species. To maintain its high level genetic diversity, it mill he necessary to use large and diverse sources of parental fish for artificial reproduction.

Molecular identification and expression analysis of natural resistance associated macrophage protein (Nramp) cDNA from Japanese flounder (Paralichthys olivaceus)

Natural resistance associated macrophage protein (Nramp) controls partially innate resistance to intracellular parasites. Its function is to enhance the ability of macrophages to kill pathogens. However, little is known about the structure and function of Nramp in lower vertebrates such as teleosts. We have recently isolated a cDNA encoding Nramp from Japanese flounder (Paratichthys olivaceus). The full-length cDNA of the Nramp is 3066 bp in length, including 224 bp 5' terminal UTR, 1662 bp encoding region and 1180 bp 3' terminal UTR. The 1662-nt open reading frame was found to code for a protein with 554 amino acid residues. Comparison of amino acid sequence indicated that Japanese flounder Nramp consists of 12 transmembrane (TM) domains. A consensus transport motif (CTM) containing 20 residues was observed between transmembrane domains 8 and 9. The deduced amino acid sequence of Japanese flounder had 77.30%, 82.71%, 82.67%, 79.64%, 80.72%, 90.97%, 91.16%, 60.14%, 71.48%, 61.69%, 72.37% identity with that of rainbow trout Nramp alpha and beta, channel catfish Nramp, fathead minnow Nramp, common carp Nramp, striped sea bass Nramp, red sea bream Nramp, mouse Nramp 1 and 2, human Nramp 1 and 2, respectively. RT-PCR indicated that Nramp transcripts were highly abundant in spleen, head kidney, abundant in intestine, liver and gill, and less abundant in heart. The level of Nramp mRNA in embryos gradually increases during embryogenesis from 4 h (8 cell stage) to 80 h (hatched stage) after fertilization. (c) 2005 Elsevier Ltd. All rights reserved.

Identification of immune genes in grass carp Ctenopharyngodon idella in response to infection of the parasitic copepod Sinergasilus major

The parasitic copepod Sinergasilus major is an important pathogen of grass carp Ctenopharyngodon idella. To understand the immune response of grass carp to the copepod infection, suppression subtractive hybridization method was employed to characterize genes up-regulation during the copepod infection in liver and gills of the fish. One hundred and twenty-two dot blot positive clones from infected subtracted library were sequenced. Searching available databases by using these nucleotide sequences revealed that 23 genes are immune-related, including known acute-phase reactants, and four novel genes encoding proteins such as source of immunodominant MHC-associated peptides (SIMP), TNF receptor-associated factor 2 binding protein (T2BP), poliovirus receptor-related protein 1 precursor, glycoprotein A repetitions predominant (GARP). The differential expression of seven immune genes, i.e. GARP, alpha-2-macroglobulin, MHC class I, C3, SIMP, T2BP, transferrin, as a result of infection was further confirmed by RT-PCR, with the up-regulation of alpha-2-macroglobulin, MHC class I, C3, SIMP and T2BP in the liver of infected fish, and down-regulation of SIMP in the gills of infected fish. The present study provides foundation for understanding grass carp immune response and candidate genes for further analysis.

The reproductive strategies of an endemic Tibetan fish, Gymnocypris selincuoensis

The reproductive traits of Gymnocypris selincuoensis from Selincuo Lake and its tributaries were investigated in 1997 and 1998. The youngest mature male was age 7 with a standard length (SL) of 172.0 mm, and the youngest mature female was age 8 with a SL of 194.0 mm. The L(50)s Of SL and age at first maturity were respectively 250.32 mm and age 9 for males and 224.71 mm and age 8 for females. The gonadosomatic index (GSI) significantly changed with seasons for mature individuals but not for immature individuals. GSIs of mature females at stages IV and V of ovary development increased with SL and reached a maximum value at the SL range from 370 mm to 390 mm; the GSIs of mature males were negatively correlated with SL. The breeding season lasted from early April to early August. Egg size did not significantly change with SL but increased with the delay of spawning. The individual absolute fecundity varied from 1,341 to 28,002 eggs (mean 12,607+/-7,349), and the individual relative fecundity varied from 6.4 to 42.0 eggs.g(-1) (mean 25.5+/-9.7). The individual fecundity increased with total body weight; it also increased with SL for those of SL less than 370 mm. There was a rest of spawning for mature individuals.

Deep level and photoluminescence studies of Er-implanted GaN films

Deep level transient spectroscopy measurements were performed on the metal organic chemical vapor deposition epitaxially grown GaN before and after the implantation with Er. Only one deep level located at 0.270 eV below the conduction band was found in the as-grown GaN films. But four defect levels located at 0.300, 0.188, 0.600 and 0.410 eV below the conduction band were found in the Er-implanted GaN films after annealing at 900 degrees for 30 min. The origins of the deep defect levels were discussed. The photoluminescence (PL) properties of Er-implanted GaN thin films were also studied. After annealing at 900 degrees for 30 min in a nitrogen flow, Er-related 1.54 mu m luminescence peaks could be observed for the Er-implanted GaN sample. Moreover, the energy-transfer and recombination processes of the Er-implanted GaN film were described. (c) 2006 Elsevier B.V. All rights reserved.

Electronic structure and electron g factors of HgTe quantum dots

The electronic structure and electron g factors of HgTe quantum dots are investigated, in the framework of the eight-band effective-mass approximation. It is found that the electron states of quantum spheres have aspheric properties due to the interaction between the conduction band and valence band. The highest hole states are S (l = 0) states, when the radius is smaller than 9.4 nm. the same as the lowest electron states. Thus strong luminescence from H-Te quantum dots with radius smaller than 9.4 nm has been observed (Rogach et al 2001 Phys. Statits Solidi b 224 153). The bandgap of H-Te quantum spheres is calculated and compared with earlier experimental results (Harrison et al 2000 Pure Appl. Chem. 72 295). Due to the quantum confinement effect, the bandgap of the small HgTe quantum spheres is positive. The electron g factors of HgTe quantum spheres decrease with increasing radius and are nearly 2 when the radius is very small. The electron g factors of HgTe quantum ellipsoids are also investigated. We found that as some of the three dimensions increase, the electron g factors decrease. The more the dimensions increase, the more the g factors decrease. The dimensions perpendicular to the direction of the magnetic field affect the g factors more than the other dimension.

Numerical simulation of nc-Si : H/c-Si heterojunction solar cells

AMPS simulator, which was developed by Pennsylvania State University, has been used to simulate photovoltaic performances of nc-Si:H/c-Si solar cells. It is shown that interface states are essential factors prominently influencing open circuit voltages (V-OC) and fill factors (FF) of these structured solar cells. Short circuit current density (J(SC)) or spectral response seems more sensitive to the thickness of intrinsic a-Si:H buffer layers inserted into n(+)-nc-Si:H layer and p-c-Si substrates. Impacts of bandgap offset on solar cell performances have also been analyzed. As DeltaE(C) increases, degradation of VOC and FF owing to interface states are dramatically recovered. This implies that the interface state cannot merely be regarded as carrier recombination centres, and impacts of interfacial layer on devices need further investigation. Theoretical maximum efficiency of up to 31.17% (AM1.5,100mW/cm(2), 0.40-1.1mum) has been obtained with BSF structure, idealized light-trapping effect(R-F=0, R-B=1) and no interface states.

Effect of rapid thermal annealing on electron emission and DX centers in strained InGaAs/GaAs single quantum well laser diodes

Thermal processing of strained In0.2Ga0.8As/GaAs graded-index separate confinement heterostructure single quantum well laser diodes grown by molecular beam epitaxy is investigated. It is found that rapid thermal annealing can improve the 77K photoluminescence efficiency and electron emission from the active layer, due to the removal of nonradiative centers from the InGaAs/GaAs interface. Because of the interdiffusion of Al and Ga atoms, rapid thermal annealing increases simultaneously the density of DX centers in the AlGaAs graded layer. The current stressing experiments of postgrowth and annealed laser diodes are indicative of a corresponding increase in the concentration of DX centers, suggesting that DX centers may be responsible for the degradation of laser diode performance.

Growing process of CdS nanoclusters in zeolite Y studied by positron annihilation

Zeolite Y has been used as the host to generate CdS nanoclusters. The location of CdS nanoclusters inside zeolite hosts was confirmed by the blue-shifted reflection absorption spectra with respect to that of bulk CdS materials. But which kind of cage inside zeolite Y, sodalite cage or supercage, was preferred for the CdS clusters remained unclear. In this paper, we conducted positron annihilation spectroscopy (PAS) measurements for the first time on a series of CdS/Y zeolite samples and concluded that CdS clusters were not located in supercages but in smaller sodalite cages. The stability of CdS clusters inside the sodalite units was due to the coordination of Cd atoms with the framework oxygen atoms of the double six-ring windows. Moreover, PAS revealed some important information of surface states existing on the interfacial layers between CdS clusters and zeolite Y. (C) 2001 Elsevier Science B,V, All rights reserved.