烤烟漂浮育苗影响因素研究进展

烤烟漂浮育苗技术是我国烤烟育苗的主要方式,对烤烟生产具有重要影响。综述了烤烟漂浮育苗的影响因素,总结了育苗基质、营养液、育苗盘、剪叶、温度和光等对漂浮育苗的影响,并对今后烤烟漂浮育苗的研究方向进行了展望。     

基质改良对河岸带芦苇区冬季脱氮效果及土壤-植物化学计量特征的影响

为探究基质改良对亚热带地区河岸带芦苇区冬季脱氮效果和土壤-植物化学计量特征的影响,以河岸带土壤基质为对照,通过芦苇湿地模拟实验,系统探讨不同基质(砾石、砾石+生物炭、陶粒+生物炭、改性陶粒+生物炭)添加条件下,芦苇湿地的冬季脱氮效果,以及土壤和植物各器官中C、N、P含量及其化学计量比。结果表明：基质改良能够提高芦苇湿地冬季脱氮效果,添加砾石处理使NH₄⁺-N去除率提高8.3个百分点(P<0.05),添加砾石+生物炭处理使TN和NH₄⁺-N去除率均提高8.9个百分点(P<0.05)。基质改良能够增加土壤TC、TN和TP含量,其中,添加砾石+生物炭处理使三者含量均显著增加(P<0.05)。添加生物炭的3个处理均有利于根C固定和植物N吸收,添加陶粒+生物炭和改性陶粒+生物炭处理对植物生长具有促进作用。土壤-植物化学计量特征存在一定的相关性,且土壤与植物茎和根之间的关系更大;与植物相比,基质改良使芦苇湿地冬季脱氮效果更易受到土壤化学计量特征的影响。研究表明,适当的基质改良能够提高亚热带地区...     

Use of GIS to predict effects of water level on the spawning area for smelt, Retropinna retropinna, in Lake Taupo, New Zealand

A GIS model of the littoral bathymetry and substrate composition of Lake Taupo was created using ArcInfo. Littoral substrates were mapped by aerial photography and confirmed by ground-truthing. Water depths were determined by echosounding linked to a differential GPS. These data were imported into ArcInfo where a 3D GIS model was used to calculate the total area of smelt, Retropinna retropinna Richardson, spawning habitat (i.e. clean sand between depths of 0.5–2.5 m) at each of five lake levels. There was little change in area over the first 50 cm below the natural maximum lake level, but spawning habitat decreased rapidly over the next 1.4 m such that a 30% reduction occurred at the natural minimum level. Anecdotal information on inter-annual variations in lake level and smelt abundance supported the notion that high lake levels in spring result in high recruitment of smelt. The GIS model also predicted effects of lake level change on areas of macrophyte cover and on other littoral substrates, and could be used to assess effects of lake level changes on the habitats of other biota.     

Ontogenic changes in the digestive enzyme patterns and characterization of proteases in Indian major carp Cirrhinus mrigala

Digestive enzymes of Cirrhinus mrigala (Ham.) were studied during ontogenic development. Specific amylase activity was detected in first feeding fish. The enzyme activity decreased up to day‐18 and then it increased with the age of fish to reach the highest level on day‐34. Protease activity was 28.61 ± 8.90 mU mg protein^?1 min^?1 on day‐4 and increased with the age throughout the study period. Trypsin activity was 31.86 ± 1.12 mU mg protein^?1 min^?1 on day‐4. The activity decreased up to day‐10 and from day‐12 onwards increased up to day‐26. Chymotrypsin activity was 14.56 ± 2.74 mU mg protein^?1 min^?1on day‐4 and constantly increased up to day‐26. A significant increase in lipase activity was observed between days‐24 and 34. SDS‐PAGE and substrate SDS‐PAGE showed the diversity of protein (17.4–127.8 kDa) and protease activity bands (16.6–88.8 kDa) during ontogenesis. Soybean trypsin inhibitor, phenyl methyl sulphonyl fluoride, N‐α‐p‐tosyl‐l ‐lysine chloromethylketone and N‐tosyl‐l ‐phenylalanine chloromethylketone inhibited the protease activity up to 79.72–97.21, 65.55–94.83, 45.41–75.31 and 40.78–64.72%, respectively. Inhibition study in substrate SDS‐PAGE revealed the abundance of serine proteases and the presence of isoforms of trypsin and chymotrypsin. Ethylenediamine‐tetraacetate showed 5.56–22.78% inhibition of metal ion‐specific enzyme activity.     

Efficacy of Sarafloxacin Hydrochloride in Treating Naturally-Induced Edwardsiella ictaluri Infections in Channel Catfish,Ictalurus punctatus

Sarafin (sarafloxacin hydrochloride), a new antibacterial, was evaluated in the field on a naturally induced infection of Edwardsiella ictaluri in channel catfish, -Ictalurus punctatus. Healthy channel catfish (mean weight = 50 g) were stocked into nine cages at 200 fish per cage in a pond with an undergoing E. ictaluri infection. Seven days after stocking, dead fish were observed in the cages with clinical signs of enteric septicemia of channel catfish (ESC). After E. ictaluri was confirmed through isolative biochemical tests, medicated feed was applied for five consecutive days. During this period, fish in three control cages received a commercial 32% protein floating feed, three other cages of fish served as positive controls and were fed Romet, and three cages received the test feed with Sarafin. Both medicated feeds reduced the increase in cumulative percent mortality. In the control cages, cumulative percent mortalities continued to increase throughout the study period. Average daily mortality rates were significantly lower following both treatments of medicated feed, and treatments receiving Sarafin showed the greatest reduction in average daily mortality rates. Average daily mortality rates in the control did not change after the medicated feeding period. Toward the end of the study, temperatures reached 30°C, above the active range of ESC infections, and all mortalities ceased.     

Biochemical indices (RNA/DNA ratio and protein content) in studying the nutritional status of Ruditapes decussatus (Linnaeus 1758) juveniles

In this work, we investigated the nutritional status of Ruditapes decussatus juveniles under different rearing conditions, using biochemical indices (RNA/DNA ratio and protein content) and the linear instantaneous growth rate (IGR). Two experiments were conducted to study the effect of starvation, addition of substrate (sand) as rearing support and diet composition on somatic growth and biochemical indices. Results show that biochemical indices of fed juveniles were significantly (P<0.05) higher. Highest RNA/DNA values and protein content were recorded in fed juveniles reared with substrate (P<0.05); conversely, lowest values were recorded in starved ones reared without substrate. In the second experiment, the highest RNA/DNA ratio was recorded in juveniles fed with control algal mixture composed of species commonly used in bivalve nurseries [Isochrysis galbana (clone T-Iso), Chaetoceros calcitrans and Tetraselmis suecica] and lowest in those fed with algal species isolated from Tunisian coasts. This confirms the usefulness of the RNA/DNA ratio and protein content in the clam's nutritional status evaluation. This assay is useful to provide information about the nutritional status and health of the clam in field conditions.     

Substrate concentration affects the in vitro metabolism of 17-hydroxyprogesterone by ovaries of the carp,Cyprinus carpio

Carp ovarian tissue was incubated with ³H-17-hydroxyprogesterone in the presence of 0, 0.1, 1, 10, and 100 μg ml⁻¹ unlabeled 17-hydroxyprogesterone. The pattern of metabolites formed showed a marked variation with substrate concentration. Formation of glucuronide and sulphate conjugates was important only at low substrate concentration. At high substrate concentration (10 and 100 μg ml⁻¹) 17,20α-dihydroxy-4-pregnen-3-one was the major metabolite, but at intermediate concentrations polar 7α-hydroxypregnanetetrols predominated. The results support the hypothesis that at low substrate concentrations conjugating, 5α-reducing and 7α-hydroxylating enzymes, of high activity but low capacity, act as scavengers to deactivate any steroids formed during the relatively low pituitary gonadotrophin secretions which are necessary for oocyte development, but that during the prespawning gonadotrophin surge when high levels of substrate are present these enzymes are saturated and 17,20α-dihydroxy-4-pregnen-3-one (17,20αP) becomes the major ovarian steroid. The possible role of 17,20αP during oocyte final maturation requires further examination.     

Competition for food between Eurasian perch (Perca fluviatilis L.) and ruffe (Gymnocephalus cernuus [L.]) over different substrate types

Abstract –  Food consumption by Eurasian perch ( Perca fluviatilis L.) and ruffe ( Gymnocephalus cernuus [L.]) was studied in single and mixed-species treatments in the laboratory, where alternative food resources, chironomids and zooplankton, were offered simultaneously. The effects of structural complexity, which was represented by substrate grain size, and of feeding level on food consumption were analysed. Across all experiments, the outcome of competition between perch and ruffe depended on food abundance and on the structural complexity of the environment. Perch and ruffe both changed their food consumption in the presence of a heterospecific competitor. With high food supply, perch consumed more benthic food than ruffe. With low food supply, the consumption of perch decreased strongly, while that of ruffe remained high on fine sediment. Under all conditions tested, the mechanism of competition appeared to be of interference rather than of exploitative nature. It is suggested that with decreasing lake productivity caused by re-oligotrophication, habitat shifts of both species will occur, which will alleviate interspecific competition. Ruffe will forage over fine sediment and perch over coarse sediment, whereby both species will achieve the highest foraging efficiency under conditions of low food supply.     

植物收割对人工湿地基质酶活性的影响

研究了7月份植物收割对人工湿地基质磷酸酶、脲酶、蛋白酶、脱氢酶活性及养殖废水中总氮(TN)、总磷(TP)、COD去除率的影响。结果显示:植物收割后磷酸酶、脲酶、蛋白酶活性开始增高,分别于第20天(13.7 mg/100 g)、第16天(1.9 mg/100 g)、第12天(61.7 mg/100 g)达到最大值,均于第28天(10.1 mg/100 g、1.1 mg/100 g、43.2 mg/100 g)恢复到收割前水平。脱氢酶活性在植物收割后第4天(142.3μL/100 g)降到最小值,此后开始增高,第16天(249.5μL/100 g)达到最大值,于第24天(195.6μL/100 g)恢复到收割前水平。净化效果研究表明,植物收割后TP、TN去除率开始增高,分别在植物收割后第20天(75.1%)、16天(60.6%)达到最大值,均于第28天(51.1%、34.1%)恢复到收割前水平。COD去除率在收割后第4天(25.3%)降到最小值,此后开始增高,第16天(70.2%)达到最高值,第24天(46.5%)恢复到收割前水平。