Fluxes and storage of fine-grained sediment and associated contaminants in the Na Borges River (Mallorca,Spain)

Samples of suspended and fine channel bed sediment were used to examine the spatial and temporal variability in the amount of fine-grained sediment and associated contaminants temporarily stored in the Na Borges River (319 km²) in Mallorca and the relationship of such channel storage to the fluxes of fine sediment and associated contaminant through the system. This Mediterranean groundwater-dominated river drains a predominantly agricultural catchment, although urbanisation during the twentieth century has changed the catchment hydrology. A re-suspension technique was used to obtain estimates of channel storage at monthly intervals during the 2004–2005 hydrological year at eight locations along the main stem of the stream (i.e. 26 km). The estimates of fine sediment storage ranged between 0 and 13,000 g m^− 2, with a mean value of 2400 g m^− 2. Only Cu exceeded the critical threshold (36 μg g^− 1), established by existing guidelines for the contaminant content of fluvial sediment. The results demonstrated significant spatial and temporal variability, in response to the influence of urban point sources, agricultural practises, seasonal groundwater interactions and the first-flush effect. The amount of fine sediment entering storage during the study period was 515.2 t, representing the net increase in storage over the study period. As a result, the mean specific storage was 21 t km^− 1. Suspended-sediment load and temporary fine sediment storage are the two basic components of the channel sediment budget that interact to determine sediment transport through a channel system, and they can therefore be used to compute the total input of sediment and associated contaminants to the system. Accordingly, storage values were compared with estimates of suspended sediment load and associated contaminant load values at three measuring stations along the river. During the study period, storage in the main channel system represented 87% of the sediment input and 68% of the contaminant input, indicating that deposition was more important than transport. The low gradient of the main channel and the low return period (i.e. 0–2.5 years) of the flood events that occurred during the study period meant that remobilised bed sediment and associated contaminants were redeposited downstream rather than being flushed to the catchment outlet as suspended sediment. Furthermore, the river bed is dry during the summer months, allowing sealing and crusting processes to stabilise the sediment deposited during the wet season and thereby reduce its availability for remobilisation at the beginning of the next wet season. Together, these factors promote sediment deposition and storage, with the result that sediment progressively accumulate over several hydrological years until a major flood event (i.e. return period ≈ 5 years) evacuates the stored sediment.     

Leukocyte and thrombocyte reference values for channel catfish (Ictalurus punctatus Raf), with an assessment of morphologic, cytochemical, and ultrastructural features

BACKGROUND: Hematology tests are useful to evaluate physiologic disturbances in fish and can provide important information for the diagnosis and prognosis of disease. OBJECTIVES: The primary purpose of this study was to define reference intervals for thrombocytes and leukocytes in healthy channel catfish (Ictalurus punctatus). In addition, the morphologic, cytochemical, and ultrastructural features of blood cells were assessed. METHODS: Blood samples (0.5 mL) were collected into EDTA from 40 clinically healthy catfish on a commercial fish farm in Jaboticabal, Brazil. Thrombocyte, total WBC, and differential WBC counts were determined and reference intervals were calculated as the 25-95th percentiles of data. Thrombocyte and leukocyte morphology was assessed in blood smears stained with May Grünwald-Giemsa-Wright and ultrastructurally by transmission electron microscopy. Cytochemical staining patterns were described using periodic acid-Schiff (PAS), peroxidase, nonspecific esterase, alkaline phosphatase, and toluidine blue. RESULTS: Reference intervals were as follows: thrombocytes 58,802-99,569/microL; total WBCs 27,460-41,523/microL; lymphocytes 5380-11,581/microL; monocytes 2949-7459/microL; neutrophils 12,529-22,748/microL, and basophils 736-2003/microL. Neutrophils were positive for peroxidase and PAS; monocytes were positive for nonspecific esterase; and basophils were positive with toluidine blue. CONCLUSION: The morphologic and staining features of neutrophils and monocytes of channel catfish are similar to those of mammals, and the presence of basophils in this species was verified. These reference intervals and morphologic findings provide a foundation for future investigations on the functions and alterations of blood cells in channel catfish.     

大豆中GmKAB1基因的克隆和信息学分析

为探讨GmKAB1在大豆处于低钾胁迫下的表达水平,以大豆钾高效品系油06-71和钾敏感型品系衡春04-11为试验材料,设置低钾胁迫试验,分别在处理后0.5h、2h、6h、12h、3d、6d、9d和12d取样提取RNA,利用Real time-PCR检测各时间段GmKAB1基因的表达量。结果显示GmKAB1基因在地下部分表达比地上部持续时间更长,地下部相对表达倍数最高为3.5,较地上部相对表达倍数更高。克隆目的基因并对基因序列进行同源性及生物信息学分析,结果表明,与GmKAB1基因相似性在30%以上的同源基因有45个,GmKAB1在进化树中的位置与Glyma20g19000最近;GmKAB1编码蛋白为稳定的可溶性蛋白,具有2个保守结构域,多个磷酸化位点,表明在受到低钾胁迫后该基因编码的β亚基与α亚基结合调控电压门控钾离子通道,对大豆从根部获取钾离子可能起着关键作用。     

青海省新型现代农业科技通道建设研究

分析了青海省农业科技通道建设存在的制度不健全,人员队伍素质偏低等问题,指出建立和完善农技服务通道、反馈通道和评价通道是建设新型现代农业科技通道的主要内容。在此基础上提出了相应的对策,即建立以"专家—农技人员—科技示范户"为主线的农业科技成果转化应用快速通道。     

Effects of Feeding Diets with and without Fish Meal on Production of Channel Catfish,Ictalurus punctatus,Stocked at Varying Densities

ABSTRACT

Animal protein, generally fish meal, has traditionally been used in the diet of channel catfish. However, our previous research indicates that animal protein is not needed for growing stocker-size catfish to food fish when the fish are stocked at densities typical of those used in commercial catfish culture. Whether this holds when fish are stocked at high densities is not known; thus, we conducted an experiment to evaluate the effect of feeding diets with and without fish meal to channel catfish stocked in earthen ponds at different densities. Two 32% protein-practical diets containing 0% or 6% menhaden fish meal were compared for pond-raised channel catfish, Ictalurus punctatus, stocked at densities of 14,820, 29,640, or 44,460 fish/ha. Fingerling channel catfish with average initial weight of 48 g/fish were stocked into 30 0.04-ha ponds. Five ponds were randomly allotted for each fish meal level?×?stocking density combination. Fish were fed once daily to satiation for two growing seasons. There was a significant interaction between stocking density and fish meal for net production; net production increased in fish fed a diet containing fish meal compared with those fed an all-plant diet at the highest stocking density, but not at the two lower stocking densities. Net production of fish fed diets with and without fish meal increased as stocking density increased. Viewing the main effect means, weight gain decreased and feed conversion ratio increased for fish stocked at the two highest densities, and survival was significantly lower at the highest stocking density. Visceral fat decreased in fish at the two highest stocking densities. Body composition data were largely unaffected by experimental treatment except for a reduction in percentage filet fat in fish at the highest stocking density, and fish that were fed diets containing fish meal had a lower percentage fillet protein and a higher percentage fillet fat. It appears that at stocking densities two to three times higher than generally used, animal protein (fish meal) may be beneficial in the diet of channel catfish. In regard to stocking densities, high stocking results in higher overall production, but the average fish size decreased as stocking density increased.     

Effects of 28% Protein Diets Differing in Quality on Channel Catfish Performance,Processing Traits,and Production Economics in a Multi-Batch System

Three 28% protein feeds (premium, standard, or a low-cost diet) were fed to channel catfish in a pond study to compare growth, production, and costs as a follow up to similar work with 32% protein feeds. Twelve 0.1-ha earthen ponds at the University of Arkansas at Pine Bluff (UAPB) Aquaculture Research Station were stocked with carryover fish (0.39 kg mean weight) at 5,860 fish/ha and fingerling catfish (mean individual weight of 15.4 g) at 12,500 fish/ha. Total yield (gross and net) did not differ between fish fed the premium as compared to the standard diet, but that of the premium diet was significantly higher than that of fish fed the low-cost diet. The feed conversion ratio (FCR) did not differ between fish fed the premium and standard diets, but was lower than the FCR of fish fed the low-cost diet. There were no differences found in processing yields among treatments. Given the lower cost of the 28% standard diet and yields equivalent to those of the 28% premium diet, the 28% standard diet was economically preferable to the other diets tested.     

Peracetic acid is effective for controlling fungus on channel catfish eggs

Peracetic acid (PAA) is a relatively new compound suggested for use to treat pathogens in aquaculture. It is approved for use in Europe, but not in the United States. This study determined the effectiveness of PAA for fungus control on channel catfish, Ictalurus punctatus (Rafinesque), eggs. The study consisted of five PAA concentrations (2.5, 5, 10, 15 and 20 mg L^?1) and an untreated control in a flow‐through system. A single spawn was used for each replication (N = 4). Eggs were treated twice daily until the embryos developed eyes. When hatching was complete for all viable eggs, fry were counted to determine the percent survival in each treatment. Fungal growth was severe in the untreated controls resulting in 11% survival. Treatments of 2.5, 5 and 10 mg L^?1 PAA were significantly different from the controls (P < 0.05). The highest percent survival of hatched fry was with 5 mg L^?1 PAA administered twice daily; the 2.5 mg L^?1 PAA treatment had slightly less survival, but gives a higher margin of safety in case of treatment error. Very little fungus was present in treatments receiving 2.5 mg L^?1 PAA or higher, and concentrations of 15 and 20 mg L^?1 PAA were toxic to the eggs. The mean survivals in the 0, 2.5, 5, 10, 15 and 20 mg L^?1 PAA treatments were 11%, 60%, 63%, 62%, 32% and 0%, respectively. Therefore, PAA may be a compound that merits further investigations regarding its use in U.S. aquaculture.     

对我省绿色通道建设的思考

近年公路绿化进展较快,取得了一定成绩,由于我省地处青藏高原,地形、地貌复杂,气候特殊,绿化美化制约条件很大,还存在一些问题,针对问题提出了改进措施,供今后实施中参考。     

农业产业化与农民增收渠道研究

我国处于农业产业化的初级阶段,各种类型的农业产业化不断出现。从农业产业化涵义和表现形式出发,分析了农业产业化形成过程及在这一过程中农民增收的渠道,提出了农业产业化需要注意的问题。