An evaluation of fish health‐management practices and occupational health hazards associated with Pangasius catfish (Pangasianodon hypophthalmus) aquaculture in the Mekong Delta,Vietnam

This study aimed to evaluate the current status on the use of probiotics, disinfectants and antimicrobials in hatcheries, nurseries and grow‐out farms producing Pangasius catfish (Pangasianodon hypophthalmus) in the Mekong Delta, Vietnam. Semi‐structured interviews were conducted with 83 aquaculture enterprises (15 hatcheries, 32 nurseries and 36 grow‐out farms). Farmers reported use of a total of 24 different antimicrobials, e.g. for treatment of bacillary necrosis and motile aeromonad septicaemia, and a variety of disinfectants, probiotics and nutritional supplements. In contrast to small‐scale farmers, all large‐scale grow‐out farmers studied were certified and therefore had higher levels of formal education and specialized aquaculture training to diagnose and treat diseases. All farmers prepared their own medicated feed with a high risk of treatment failure, negative environmental impact from released antimicrobials and resistance development. Small‐scale farmers were at particular occupational health risks when handling antimicrobials and other chemicals, e.g. mixing medicated feed with bare hands. There is an urgent need to improve knowledge and use innovative approaches, e.g. private‐public partnerships, to assure a prudent use of chemicals, to improve capacity and access to disease diagnosis, particularly for small‐scale grow‐out farmers and nurseries. Efforts to control use of antimicrobials in aquaculture should be coordinated with the livestock and human health sectors taking an One‐Health approach.     

基于热重红外联用技术的竹综纤维素热解过程及动力学特性

利用热重红外联用技术(TG-FTIR)研究了竹材综纤维素在不同升温速率下(5.0, 10.0, 15.0, 20.0和30.0℃·min-1)的热解特性和热解动力学。热重分析/热重一次微分曲线(TG/DTG)表明:竹材综纤维素热解可分为干燥、快速裂解和慢速裂解等3个阶段; 随着升温速率增加, TG/DTG曲线往高温一侧移动; 竹综纤维素热解过程发生复杂的化学反应, 包括多重、平行和连续反应; 热解挥发分主要由小分子CO, H₂O, CH₄和CO₂, 以及一些醛类、酮类、酸类、烷烃、醇类和酚类等有机物组成。利用无模式函数积分法, 即Flynn-Wall-Ozawa(FWO)和Kissinger-Akahira-Sunose(KAS)积分法, 对其热解动力学进行研究。结果表明:竹材综纤维素的活化能随着转化率的升高先增大后减小再增大, 活化能数值的变化与纤维素/半纤维素不同的热解特性有紧密联系。     

Low numbers of repeat units in variable number of tandem repeats (VNTR) regions of white spot syndrome virus are correlated with disease outbreaks

White spot syndrome virus (WSSV) is the most important pathogen in shrimp farming systems worldwide including the Mekong Delta, Vietnam. The genome of WSSV is characterized by the presence of two major ‘indel regions’ found at ORF14/15 and ORF23/24 (WSSV‐Thailand) and three regions with variable number tandem repeats (VNTR) located in ORF75, ORF94 and ORF125. In the current study, we investigated whether or not the number of repeat units in the VNTRs correlates with virus outbreak status and/or shrimp farming practice. We analysed 662 WSSV samples from individual WSSV‐infected Penaeus monodon shrimp from 104 ponds collected from two important shrimp farming regions of the Mekong Delta: Ca Mau and Bac Lieu. Using this large data set and statistical analysis, we found that for ORF94 and ORF125, the mean number of repeat units (RUs) in VNTRs was significantly lower in disease outbreak ponds than in non‐outbreak ponds. Although a higher mean RU number was observed in the improved‐extensive system than in the rice‐shrimp or semi‐intensive systems, these differences were not significant. VNTR sequences are thus not only useful markers for studying WSSV genotypes and populations, but specific VNTR variants also correlate with disease outbreaks in shrimp farming systems.     

Preparation of oligoalginate plant growth promoter by γ irradiation of alginate solution containing hydrogen peroxide

Degraded alginate compounds with molecular weights of 7-26, 40-77, or 11-26 kDa were obtained by γ irradiation, hydrogen peroxide (5% H(2)O(2)) treatment, or a combination treatment involving ionizing radiation and H(2)O(2), respectively. The 14 kDa oligoalginate, prepared by the combined method, promoted the growth of mustard greens and lettuce at an optimal concentration of 75 mg/L. The growth promotion effects of the oligoalginate prepared by γ irradiation in the presence of H(2)O(2) were statistically equivalent to those of the oligoalginate prepared by γ irradiation only. The combination of γ irradiation and H(2)O(2) reduced the required irradiation dosage by a factor of 9 relative to the oligoalginate produced by γ irradiation only. The combination treatment (γ irradiation/H(2)O(2)) may be carried out on a large scale at low cost to produce oligoalginate for use as a plant growth promoter in agricultural industries.     

Spatiotemporal rescue of memory dysfunction in Drosophila

We have developed a method for temporal and regional gene expression targeting (TARGET) in Drosophila and show the simultaneous spatial and temporal rescue of a memory defect. The transient expression of the rutabaga-encoded adenylyl cyclase in the mushroom bodies of the adult brain was necessary and sufficient to rescue the rutabaga memory deficit, which rules out a developmental brain defect in the etiology of this deficit and demonstrates an acute role for rutabaga in memory formation in these neurons. The TARGET system offers general utility in simultaneously addressing issues of when and where gene products are required.     

Effects of size and nitrite exposure on respiration,oxygen partitioning,and growth of obligate air-breathing fish Channa striata

The effects of fish size and nitrite level on metabolic rate and growth were investigated in the obligate air-breathing snakehead Channa striata, which is an important aquaculture species in Vietnam. Channa striata displayed respiratory size dependence, whereby the standard metabolic rate (SMR) and routine metabolic rate (RMR) decreased progressively in an exponential manner as fish size increased from 50 to 200 g. A mildly elevated nitrite level of 5% of the LC₅₀ 96 h (12 mg NO₂^?/L or safe concentration) induced significant increases in Channa striata SMR and RMR, which were almost double that of the control at the same size. At mild elevation, nitrite caused no significant effect on fish growth and survival during 3 months of rearing. However, both growth and survival rates of fish reared at severely elevated nitrite levels were significantly lower than those of the control; in particular, survival rates were under 50%. While changes in size reduced SMR and RMR, the percentage of air oxygen partitioning remained unchanged. Channa striata upregulation of SMR and RMR and air-breathing regulation were not significantly proven in this study. In summary, maintaining water environments at levels lower than 12 mg NO₂^?/L with ample oxygenation will not affect the growth and survival rate of snakeheads.

     

Pond production of the mud crabs Scylla paramamosain (Estampador) and S. olivacea (Herbst) in the Mekong Delta, Vietnam, using two different supplementary diets

The production performance of Scylla paramamosain and S. olivacea reared together in ponds and provided with different supplementary diets (crustaceans or trash fish) were evaluated with that of an unfed control group relying only on natural food available within the pond. Each treatment was conducted in triplicate. The aim was to evaluate two production strategies over a 130‐day grow‐out trial: (1) production to 200 g crab^?1, which is the minimum preferred marketable size in the Lower Mekong Delta (LMD) and (2) production to 300 g crab^?1, the size that fetches the highest market price. Growth production models were estimated which revealed that the rearing period required to produce crabs of 200 g was 102 days with supplementary feeding, compared with 120 days for the unfed control group. The rearing period needed to produce 300‐g‐sized crabs was estimated to be 144 days and 186 days for the supplementary fed and unfed groups respectively. The additional risk involved in rearing mud crabs to 300 g is not considered worthwhile, under similar culture conditions as observed in this trial, as a decrease in pond water quality and higher mortality rates were observed in the final month of culture needed to achieve this larger size.     

River pen culture of giant freshwater prawn Macrobrachium rosenbergii (De Man) in southern Vietnam

A technical and socio‐economic survey conducted in the Dong Thap province of Vietnam to assess the current status of river pen culture of giant freshwater prawn Macrobrachium rosenbergii (De Man) showed that pen culture, which has been developed and operated by farmers' indigenous knowledge, requires more study in order to optimize stocking density and to assess its environmental impacts. In this study, the prawn pens were of rectangular shape, with an average size of 209 m². Prawns were stocked in June at an average density of 62 pieces m^?2 and fed on farm‐made feed and were harvested 2–4 times starting from 4 months after stocking until late December or the following January. The average prawn yield was 0.52 kg m^?2 year^?1, ranging from 0.14 to 1.6 kg m^?2 year^?1. The average net return was US$0.71 m^?2 year^?1, ranging from US$1.24 to 4.37 m^?2 year^?1. About 73% of the farmers achieved positive net returns. The top five constraints for prawn pen culture were lack of knowledge of culture technologies, poor water quality, disease problems, poor quality of wild seed and lack of capital. Almost all farmers have no environmental awareness, and environmental regulations for prawn pen culture have not been established. Field measurements showed that all measured water quality parameters were within the range for good growth of giant freshwater prawns, and indicated that there was no significant accumulation of nutrients and organic matter at the bottoms of rivers or canals.     

CEP peptide induces susceptibility of Arabidopsis thaliana to non-adapted pathogens

CEP peptide was synthesized and tested for induction of disease susceptibility using Arabidopsis Col-0. When Colletotrichum tropicale was used as a non-adapted fungal pathogen, the conidia germinated to form hyphal-like structures, which successfully penetrated epidermis, eventually causing disease symptoms. In such case, PEN2-, but not PEN3-dependent resistance was likely suppressed by CEP peptide. Similarly, the CEP peptide-mediated disease susceptibility was also effective to a non-adapted bacterial pathogen. Notably, such induced susceptibility was also evident on Arabidopsis mutants lacking the previously identified receptors, suggesting that the CEP peptide modulates Arabidopsis immunity through an unidentified receptor(s).

     

Evaluation of Soil Organic Matter Content under Topographic Influences in Agroforestry Ecosystems: a Study in Central Vietnam

Eurasian Soil Science - We investigate the key predictors that influence the soil organic matter (SOM) content in higher altitude plantations. This is to study the potential of carbon sequestration...