氨、亚硝酸盐和硝酸盐对凡纳滨对虾幼虾的毒性作用

研究了 NH₃-N、NO₂ ^- -N与 NO₃ ^- -N对凡纳滨对虾幼虾的毒性作用。获得了 NH₃-N_t(NH₃-N_m) 与 NO₂ ^- -N对体长2．4cm幼虾的 24h、48h、72h、96h之 LC₅₀值，两者对幼虾的安全质量分数分别为1．30 (0．101)mg/L和3．80mg/L。当 NH₃-N_t(NH₃-N_m)质量分数在1．3(0．101)~4．3(0．333)mg/L时，存活率为71．4% ~92．9%，体长增长率为36．3% ~57．1%，体重增长率为188．5% ~322．3%。当 NO₂ ^- -N质量分数在3．00~21．00mg/L时，成活率为75．0% ~91．7%，体长增长率为21．2% ~59．2%，体重增长率为72．0% ~311．9%。NO₃ ^- -N对体长7．37cm幼虾的亚急性毒性效应：NO₃ ^- -N的质量分数在 30~195mg/L时，成活率为 35% ~100%，体长增长率为8．5% ~20．5%，体重增长率为29．6% ~56．8% 。三态氮在一定质量分数范围内均对幼虾的存活率和生长率产生影响。     

中国西北地区次生盐碱水无机氮转化与环境因子的相关关系

中国西北地区次生盐碱水中NO₂^--N长期处于较高浓度，严重制约了盐碱水养殖产业的可持续发展。根据对甘肃省景泰县草窝滩渔农综合示范区（104°7''40″E，37°19''6″N）的定期定点监测，运用配对样本t检验、Duncan''s多重比较和Pearson相关性分析，研究了不同类型次生盐碱水体无机氮转化及其与环境因子的相关关系。结果表明：（1）次生盐碱水无机三态氮（NO₂^--N、NH₄⁺-N、NO₃^--N）及总氮（TN）本底值高，全年均值分别是NO₂^--N（0.3±0.2）mg/L、NH₄⁺-N（1.93±1.25）mg/L、NO₃^--N（2.92±1.5）mg/L、TN（13.91±5.85）mg/L；无机氮占TN比例不超过50%，说明有机氮在次生盐碱水体中所占比例更高；（2）环境因子pH与NO₂^--N正相关，与NO₃^--N负相关，盐度与NO₃^--N负相关，pH和盐度加剧了次生盐碱水NO₂^--N的积累；（3）水产养殖显著降低次生盐碱水体中NO₃^--N浓度和碳酸盐碱度，显示了盐碱水养殖对次生盐碱水的生态改良功能。本研究旨在为中国次生盐碱水的渔业开发利用提供科学依据。     

环境因子对鼠尾藻幼苗叶绿素荧光参数的影响

为了揭示鼠尾藻幼苗的生态适应性,研究了温度(5~34 ℃)、盐度(10~50)和营养盐等环境因子对鼠尾藻幼苗叶绿素荧光参数的影响。结果表明,(1) 氮浓度高于8 mg/L或磷浓度高于1.2 mg/L,或温度高于28 ℃,对鼠尾藻幼苗的光合作用均有显著影响(P<0.05);(2) 短时间的5~15 ℃的低温胁迫或10~50盐度胁迫6 h对鼠尾藻幼苗的F_v/F_m值影响不明显;(3) 氮、磷浓度分别为2~4 mg/L和0.2~0.8 mg/L,且NH⁺₄-N∶NO^-₃-N的比值为1~3时,较利于鼠尾藻幼苗光合作用的进行。     

高效脱氮菌强化挂膜生物滤器对海水养殖尾水净化效果研究

为了提高海水养殖尾水的净化效率, 研究了利用高效脱氮菌强化挂膜后的生物滤器对静止和流动养殖尾水的净化效果。首先利用自主筛选的 3 株适应海水环境、可有效去除氨氮、亚硝酸氮及有机物的高效脱氮菌[花津滩芽孢杆菌(Bacillus hwajinpoensis)SLWX₂、嗜碱盐单胞菌(Halomonas alkaliphila)X₃ 和麦氏交替单胞菌(Alteromonas macleodii)SLNX₂]的不同组合强化挂膜, 根据成熟后的生物滤器对定量静止养殖尾水中 NH₄⁺ -N、NO₂^– -N、NO₃^– -N、 总氮(TN)及化学需氧量(CODMn)的去除效果, 选出对各无机氮去除效果最佳的菌种组合作为强化菌种再次挂膜, 分析不同浓度强化菌种挂膜对流动养殖尾水中 NH₄⁺ -N、NO₂^– -N 和 NO₃^– -N 的持续净化效果,以上实验均以自然挂膜组为对照。静止尾水处理实验结果表明, 各实验组中 NO₃^– -N 浓度先上升后下降, 对养殖尾水各项无机氮及有机物指标的去除效果均优于对照组。其中, SLWX₂+X₃+SLNX₂ 组合高浓度组对养殖尾水中的各项指标去除效果最佳, 在第 48 小时对 NH₄⁺ -N、NO₂^– -N、CODMn 和 TN 的去除率分别达到 100%、100%、80.7%和 59.5%。而自然挂膜对照组的去除率分别为 95.5%、50.52%、38.1%、13.44%, 且 NO3– -N 浓度持续上升。说明脱氮菌强化挂膜可明显提高生物滤器对养殖尾水的净化效率, 有效降低养殖尾水中氮素和有机物的浓度。后期连续流动尾水净化实验结果表明, 实验组和对照组生物滤器出水的 NH₄⁺ -N、NO₂^– -N、NO₃^– -N 浓度均低于进水的, 强化挂膜组的又均低于自然挂膜组的, 其中 106 CFU/mL 实验组对无机氮的去除效果均最佳, NH₄⁺ -N NO₂^– -N NO₃^– -N 的最大去除率分别为 31.6%、11.33%、 15.6%; 105 CFU/mL 实验组次之, 且出水氮素浓度可长期维持在较低水平。说明脱氮菌强化挂膜对各项无机氮的去除效果持续优于自然挂膜。本实验的结果为脱氮菌在海水养殖尾水净化中的应用提供了理论基础和技术支撑。     

复合垂直流人工湿地植物与基质层微生物群落特征比较分析

为了解复合垂直流人工湿地系统对海水养殖尾水中各形态氮的处理效果, 以及植物与不同基质层微生物群落特征的相似性和差异性, 以互花米草(Spartina alterniflora)-细砂-煤渣-碎石构建的复合垂直流人工湿地系统为研究对象, 研究了该系统对海水石斑鱼养殖尾水中 COD、NO₃ ^– -N、NO₂ ^– -N、NH₄ ⁺ -N 和总氮(TN)的去除效果, 并采用高通量测序技术分析了植物根际和不同基质层微生物群落特征。结果表明, 复合垂直流人工湿地系统对污染物有较好的去除效果, 出水中 COD、NO₃ ^– -N、NO₂ ^– -N、NH₄ ⁺ -N 和 TN 的平均浓度分别为 4.00 mg/L, 0.15 mg/L, 0.16 mg/L, 0.04 mg/L, 0.64 mg/L。植物根际样品和细砂层样品的微生物群落丰富度和多样性较高, 与其他基质层样品具有明显差异; 在门分类水平上优势菌以变形菌门、拟杆菌门、放线菌门、绿弯菌门和厚壁菌门为主, 相对丰度分别为 53.7%、11.5%、11.9%、6.4%、3.7%; 在纲分类水平优势菌以 α-变形菌纲、γ-变形菌纲、放线菌纲和拟杆菌纲为主, 相对丰度分别为 30.1%、20.9%、11.9%、10.3%; 人工湿地中丰度最高的脱氮功能菌包括亚硝化单胞菌属、硝化螺菌属、 芽孢杆菌属、假单胞菌属和不动杆菌属; 系统中微生物代谢功能丰富, 且所有样品功能组成相似; 相同基质层样品的微生物群落组成差异较小, 二级湿地单元各基质层样品微生物群落的差异程度与一级湿地单元相比较小。     

生物强化反应器净化循环养殖废水的研究

利用生物膜的高效截留原理,设计了生物强化反应器,在装有弹性纤维载体的反应器内接种具有硝化反硝化作用的复合菌群,经6周左右的人工挂膜后,弹性纤维载体表面出现了肉眼可见的生物膜。试验以循环养殖废水为研究对象,探讨了不同水力停留时间(HRT)和温度(WT)对生物强化反应器净化水质效果的影响。结果显示,HRT和WT对生物强化反应器净化养殖废水效果的影响显著(P<0.05)。对HRT和WT各处理水平下的COD_Mn、TN和NH ₄-N去除率进行差异显著性分析,并综合考虑反应器的运行时间、费用和操作等因素,选取HRT=18 h、WT=30 ℃作为反应器的最佳运行条件,在此条件下反应器稳定运行3周左右。试验期间,COD_Mn、TN及NH ₄-N的平均去除率分别达44.18%、51.31%及82.08%。此外,还对反应器内载体表面的生物膜进行了可培养微生物数量动态监测。强化反应器在正式运行的25 d内,其生物膜上的可培养微生物数量不断增多,氨氧化细菌数量由35.91?10⁴ CFU/mg增长到89.43?10⁴ CFU/mg,硝化细菌数量由25.75?10⁴ CFU/mg增长到61.65?10⁴ CFU/mg,反硝化细菌数量由14.23?10⁴ CFU/mg增长到100.95?10⁴ CFU/mg；氨氧化细菌和硝化细菌在与氮素循环相关的可培养细菌中占据着主导地位(59.95%～81.25%)。脱氮细菌不断地吸附于载体表面,并成功地定殖和繁殖使得生物膜不断成熟和稳定(TN和NH ⁴-N去除率分别达51.31%及82.08%)。结果表明,生物强化反应器对循环养殖废水中COD_Mn、TN和NH ₄-N的去除效果明显。     

浙江湖州地区主养草鱼池塘水化学和浮游植物

2009年5~11月测定了浙江省湖州市南浔区花园湾村两口主养草鱼池塘的水温(T)、透明度(SD)、溶氧量(DO)、pH、电导率、盐度、总氨氮(TAN)、亚硝态氮(NO₂-N)、硝态氮(NO₃-N)、磷酸盐(PO₄-P)、总氮(TN)、总磷(TP)、高锰酸钾指数(CODMn)、叶绿素a(Chl-a)以及浮游植物的种类和密度。结果表明:池塘内的TAN为1.372~1.664 mg·L-1,NO₂-N为0.072~0.076 mg·L-1,NO₃-N为0.139~0.144·L-1,PO₄-P为0.038~0.062 mg·L-1,TN为2.267~2.828 mg·L-1,TP为0.274~0.277 mg·L-1,CODMn为15.46~15.51 mg·L-1。池塘内浮游植物优势种为蓝藻和绿藻。所检测的池塘水化学指标与20世纪80~90年代长三角地区高产鱼池相比差异不大。     

褐煤的碳缓释特征及其对池塘底泥脱氮作用的影响

厌氧氨氧化和反硝化作用是底泥生物脱氮的主要过程，碳源是调控厌氧氨氧化和反硝化作用的关键因子。本研究以褐煤为对象，对褐煤的静态碳释情况及其对池塘底泥中脱氮作用的影响进行了研究。结果显示，褐煤在室温条件下的碳释放规律符合二级动力学方程，具备作为反硝化碳源的可行性；在脱氮实验中，发现褐煤对底泥上覆水体中的亚硝酸盐氮(NNO₂^--N)的去除具有促进作用，NNO₂^--N的去除率随褐煤浓度的增加而升高，当褐煤质量浓度为40 g/L时，N\${\rm{O}}_2^ - $\-N去除率最高达99.61%，此时硝酸盐氮(NO₃^--N)的浓度也最低；同时发现，水体中氨氮(NH₄⁺-N)氧化的最适褐煤质量浓度为10 g/L，其去除率达99.39%；对底泥中的厌氧氨氧化菌群进行Illumina高通量测序发现，其中浮霉菌门占比最大(39.6%~71.8%)，优势菌属为Candidatus Brocadia (13.9%~35.8%)和Desulfovibrio (17.1%~34.8%)，添加褐煤组Candidatus Scalindua菌属比例高于未添加组；荧光定量PCR得出，随着褐煤质量浓度升高，底泥中的反硝化菌丰度呈增长趋势，而厌氧氨氧化菌丰度则低于无褐煤添加组，表明添加褐煤对底泥反硝化有促进作用，而对厌氧氨氧化有一定的抑制作用。研究表明，褐煤具备作为反硝化碳源的条件，可用于池塘养殖底泥脱氮作用。     

草鱼单养和混养池塘的水质与生物组成特征

为比较单养、混养草鱼(Ctenopharyngodon idella)养殖池塘的水质与生物组成特点，采取水质分析、环境DNA与传统鉴别方法对草鱼单养、混养(80:20)两类池塘的水质变化、浮游生物、底栖生物、菌群结构进行了分析。结果表明，混养池塘的水质优于单养池塘，混养池塘水体中总氮(TN)、硝态氮(NO_3^--N)、氨氮(NH_4⁺-N)、亚硝态氮(NO_2^--N)的浓度比单养池塘分别低10.15%、3.78%、5.07%、80.18%，总磷(TP)和活性磷(SRP)的浓度分别低27.14%和56.26%；两类池塘中浮游植物均以绿藻门(Chlorophyta)、蓝藻门(Cyanophyta)、隐藻门(Cryptophyta)为优势种，但单养池塘中的藻类密度为30×10^₆cells/L，低于混养池塘104×10^₆cells/L；两类池塘中的浮游动物均以轮虫和原生动物为优势种，枝角类和桡足类生物数量较少，单养池塘中浮游动物密度高于混养池塘；在底栖动物方面，单养池塘存在螺类、水蚯蚓和摇蚊幼虫，而混养池塘仅有螺类和摇蚊幼虫。在菌群组成方面，单养池塘水体中以厚壁菌门(Firmicutes)为优势类群，混养池塘水体中以变形菌门(Proteobacteria)为优势类群；但在两类池塘底泥中，均以变形菌门为优势类群。以上结果表明，草鱼混养有利于改善养殖池塘水质，增加浮游植物丰富度，改变养殖水体菌群的结构。本研究为优化草鱼池塘养殖结构，改善水质，构建高效池塘养殖模式提供了依据。     

鄱阳湖丰水期氮素分布特征及其与藻类的响应关系

为了探讨湖泊富营养化过程中水体氮浓度时空分布格局及其与藻类的关系,以鄱阳湖实测数据为基础,对丰水期鄱阳湖主湖区氮素的分布及其与藻类的关系进行了分析。结果表明：丰水期鄱阳湖主湖区各采样点的总氮、硝酸盐氮、氨氮的平均浓度范围分别为0.54～1.26、0.06～1.01、0.08～0.30 mg.L_^-1,外源输入及环境条件对氮素浓度分布产生了一定的影响;藻类数量与氨氮浓度相关性不明显,与总氮、硝酸盐氮浓度表现为显著负相关性,南部湖区内总氮、硝酸盐氮浓度较高,平均浓度依次为1.10 mg.L_^-1、0.75 mg.L_^-1,藻类数量较低,为1.0×10_⁶ 个/L左右;西部湖区内,氮素浓度较低,藻类生长最高值为3.5×10_⁶ 个/L左右。湖泊“中营养型”水平占主湖区的44%,“富营养型”水平占主湖区的56%,东部湖区、西部湖区是鄱阳湖富营养化风险较高区域。     

草鱼养殖水体中参与氮转化途径的异养菌分析

为分析草鱼池塘中参与氮代谢的异养细菌比例及其代谢途径,从杭州郊区取得4个草鱼池塘的水样,每个水样通过涂布随即挑选100株菌株进行定性显色试验,并据此选取11株异养菌进行16S rRNA序列分析。结果表明,4个草鱼养殖池塘中NH4+-N和NO2--N的平均水平分别为5.597 mg/L和0.135 mg/L。池塘中可培养的异养菌平均为3.26×105cfu/mL,其中的89.75%参与了氮的不同代谢途径,其中31.25%的氨化菌和33.50%NO3--N(NO2--N)还原菌参与了NH4+-N的生成,32.45%的氨氧化菌参与了NH4+-N的降低;NO2--N生成途径主要包括蛋白质直接转化(11.26%)、氨氧化(4.25%)和硝酸盐氮还原(10.75%),而NO2--N降低主要通过15.50%的亚硝酸氧化菌、8.75%的NO2--N还原菌和10.75%的反硝化菌实现。结果提示,草鱼养殖水体中存在大量的异养硝化菌参与不同的氮代谢途径,且产生氨氮的异养菌比例远高于去除氨氮的菌,这是草鱼养殖水体中氨氮含量易偏高的原因。同时,11株不同功能的异养菌16SrRNA鉴定结果为寡养食单胞菌(Stenotrophomonas)6株、假单胞菌(Pseudomonas)3株、克雷伯氏菌(Klebsiella)和肠杆菌(Enterobacter)各1株,而且细菌对氮源的利用具有菌株特异性。     

Effect of Dietary Protein Concentration on Nitrogenous Waste in Intensively Fed Catfish Ponds

Channel catfish were fed five diets containing 24, 28, 32, 36 or 40% protein in intensively stocked earthen ponds over a 141 d growing season. Mean standing crop at harvest was 7,559 kg/ha, and maximum daily feed allowance was 105 kg/ha. Dietary protein concentration had a negative linear effect on weight gain. Total ammonia-nitrogen (TAN) in pond water increased linearly as dietary protein concentration increased and was positively correlated with total protein fed. However, unionized ammonia-nitrogen (NH₃-N) was not influenced by dietary protein concentration. Dietary protein had a positive linear effect on nitrite-nitrogen (NO₁^-_- -N) concentration, which was positively correlated with total protein fed and TAN. There was no significant correlation between NO₂^-_--N and fish weight gain, although there was a significant positive correlation between NO₂^-_- -N/Cl-molar ratio in pond water and concentration of methemoglobin in the fish. Results from this study indicate that when the feeding rate is as high as 100 kg/ha/d, or 3,000 kg protein/ha/season, dietary protein concentrations of 36% and above can result in harmful concentrations of NO₂^-_--N when Cl concentration in the ponds is 2–3 mg/L. Although the NO₂^-_--N/Cl- ratio in the ponds increased to harmful levels with protein concentration of the diets, this might not be the major cause of the reduction in fish growth rate as dietary protein increased because the greatest difference in weight gain occurred at the lower protein concentrations and the greatest difference in NO₂^-_--N occurred at the higher dietary protein concentrations.     

Ammonia and nitrite toxicity to false clownfish <Emphasis Type="Italic">Amphiprion ocellaris</Emphasis>

False clownfish, Amphiprion ocellaris, is one of the most commercialized fish species in the world, highly produced to supply the aquarium market. The high stocking densities used to maximize fish production can increase ammonia and nitrite to toxic levels. In this study, A. ocellaris juveniles (1.20 ± 0.34 g) were exposed to six concentrations of ammonia ranged from 0.23 to 1.63 mg/L NH₃-N and eight concentrations of nitrite (26.3–202.2 mg/L NO₂ ^?-N). The LC₅₀- 24, LC₅₀-48, LC₅₀-72 and LC₅₀-96 h were estimated to be 1.06, 0.83, 0.75 and 0.75 mg/L for NH₃-N and 188.3, 151.01, 124.1 and 108.8 mg/L for NO₂ ^?-N. Analysis of gill lesions caused by sublethal concentrations of these nitrogenous compounds showed that both nitrogenous compounds induced tissue lesions such as hyperplasia of epithelium cells, hypertrophy of chloride cells and lamellar lifting to all concentrations tested. However, histopathological alterations were more conspicuous accordingly the increase of ammonia or nitrite in fish exposed to 0.57 mg/L NH₃-N or 100 mg/L NO₂ ^?-N. Based on our results, we recommend to avoid concentrations higher than 0.57 mg/L of NH₃-N and 25 mg/L of NO₂-N in water.     

A microplate technique to quantify nutrients (NO2−, NO3−, NH4+ and PO43−) in seawater

Many methods to measure nutrients (NO₂^?, NO₃^?, NH₄⁺, and PO₄^3?) in water are based on the formation of coloured complexes that are measured by spectrophotometry, frequently using large‐volume (10 mL) spectrophotometer cells. Miniaturization of the techniques using microplate readers and sample volumes as small as 250 μL is an affordable alternative for these determinations. This work describes the adaptation to microtechniques using a 96‐well microplate to measure nitrogen compounds and phosphate in seawater. They can be used as an inexpensive procedure for routine monitoring in aquaculture ponds because of the smaller sample, reagent requirements, and suitable ranges.     

Activated sludge denitrification in marine recirculating aquaculture system effluent using external and internal carbon sources

Stringent environmental legislation in Europe, especially in the Baltic Sea area, limits the discharge of nutrients to natural water bodies, limiting the aquaculture production in the region. Therefore, cost-efficient end-of-pipe treatment technologies to reduce nitrogen (N) discharge are required for the sustainable growth of marine land-based RAS. The following study examined the potential of fed batch reactors (FBR) in treating saline RAS effluents, aiming to define optimal operational conditions and evaluate the activated sludge denitrification capacity using external (acetate, propionate and ethanol) and internal carbon sources (RAS fish organic waste (FOW) and RAS fermented fish organic waste (FFOW)). The results show that between the evaluated operation cycle times (2, 4, and 6 h), the highest nitrate/nitrite removal rate was achieved at an operation cycle time of 2 h (corresponding to a hydraulic retention time of 2.5 h) when acetate was used as a carbon source. The specific denitrification rates were 98.7 ± 3.4 mg NO₃⁻-N/(h g biomass) and 93.2 ± 13.6 mg NO_x⁻-N/(h g biomass), with a resulting volumetric denitrification capacity of 1.20 kg NO₃⁻-N/(m³ reactor d). The usage of external and internal carbon sources at an operation cycle time of 4 h demonstrated that acetate had the highest nitrate removal rate (57.6 ± 6.6 mg N/(h g biomass)), followed by propionate (37.5 ± 6.3 mg NO₃⁻-N/(h g biomass)), ethanol (25.5 ± 6.0 mg NO₃⁻-N/(h g biomass)) and internal carbon sources (7.7 ± 1.6–14.1 ± 2.2 mg NO₃⁻-N/(h g biomass)). No TAN (Total Ammonia Nitrogen) or PO₄^3- accumulation was observed in the effluent when using the external carbon sources, while 0.9 ± 0.5 mg TAN/L and 3.9 ± 1.5 mg PO₄^3--P/L was found in the effluent when using the FOW, and 8.1±0.7 mg TAN/L and 7.3 ± 0.9 mg PO₄^3--P/L when using FFOW. Average sulfide concentrations varied between 0.002 and 0.008 mg S^2-/L when using the acetate, propionate and FOW, while using ethanol resulted in the accumulation of sulfide (0.26 ± 0.17 mg S^2-/L). Altogether, it was demonstrated that FBR has a great potential for end-of-pipe denitrification in marine land-based RAS, with a reliable operation and a reduced reactor volume as compared to the other available technologies. Using acetate, the required reactor volume is less than half of what is needed for other evaluated carbon sources, due to the higher denitrification rate achieved. Additionally, combined use of both internal and external carbon sources would further reduce the operational carbon cost.     

草鱼复合养殖系统间隙水与上覆水中营养盐分布特征

采用陆基围隔实验法,于2009年6～10月调查并分析了草鱼复合养殖系统上覆水和沉积物间隙水营养盐(NH4-N,NO3-N,NO2-N,PO4-P)的时空分布及沉积物总氮(TN)、总磷(TP)和总碳(TC)含量的变化.结果显示,(1)草鱼复合养殖系统上覆水中NH4-N,NO3-N,NOz-N和PO4-P的 含量波动范围分别为0.056～1.499、0.022～0.228、0.049～3.903、0.003～1.882 mg/L,间隙水中营养盐的平面分布中,NH4-N在总无机氮(DIN)中所占比例随着养殖时间的增加而增加,不同复合养殖系统的营养盐垂直分布特征不同,规律也不明显.(2)实验结束与实验开始时相比,沉积物中TN和TP含量无明显变化,但TC含量显著降低,以混养模式(GSC)的减少幅度最大.结果表明,在本实验条件下,草鱼、鲢鱼与鲤鱼复合养殖系统可有效降低养殖过程中有机物的积累,降低底层中潜在释放的NH4-N含量,是一种较为合理的草鱼复合养殖模式.     

主养草鱼与主养黄颡鱼池塘沉积物—水界面氮磷营养盐通量变化及与环境因子的关系

为了探讨不同主养模式池塘养殖期间沉积物—水界面氮磷营养盐通量变化特征以及与环境因子之间的相互关系,利用沉积物—水界面营养盐扩散通量的原位观测装置,分析了2013年4—10月主养草鱼和主养黄颡鱼池塘沉积物—水界面营养盐交换通量,并探讨了影响营养盐交换通量的因素。结果发现:(1)在养殖初期,各种形态氮磷在养殖池塘沉积物—水界面主要表现为从上覆水向沉积物的沉积,养殖中后期,由于温度升高以及池塘沉积物中营养物质的大量累积,各种形态氮磷表现为以沉积物向上覆水扩散为主,表明池塘沉积物是氮磷营养盐的源与汇;(2)两种不同主养模式池塘氮磷通量的统计结果表明,沉积物—水界面-N、-N和-P通量变化无显著差异,而-N、TN和TP通量有显著差异;(3)上覆水中DO含量的升高显著促进界面间-N和-N释放通量,而-N和-P释放通量与上覆水DO浓度成显著负相关;温度的升高对各种无机形态的氮磷通量有显著的促进作用。     

Evaluation of the impact of nitrate-nitrogen levels in recirculating aquaculture systems on concentrations of the off-flavor compounds geosmin and 2-methylisoborneol in water and rainbow trout (Oncorhynchus mykiss)

Aquatic animals raised in recirculating aquaculture systems (RAS) can develop preharvest “off-flavors” such as “earthy” or “musty” which are caused by the bioaccumulation of the odorous compounds geosmin or 2-methylisoborneol (MIB), respectively, in their flesh. Tainted aquatic products cause large economic losses to producers due to the inability to market them. Certain species of actinomycetes, a group of filamentous bacteria, have been attributed as the main sources of geosmin and MIB in RAS. Previous studies have demonstrated that certain nutritional factors can stimulate or inhibit bacterial biomass and geosmin production by certain actinomycetes. In the current study, the effects of two nitrate-nitrogen (NO₃^--N) levels (20–40 mg/L and 80–100 mg/L) on geosmin and MIB levels in culture water and the flesh of rainbow trout (Oncorhynchus mykiss) raised in RAS were monitored. Water and fish tissue samples were collected over an approximately nine-week period from six RAS, three replicates each of low and high NO₃^--N, and analyzed for geosmin concentrations using solid phase microextraction–gas chromatography–mass spectrometry. Results indicated no significant difference in geosmin concentrations in water or fish flesh between the low and high NO₃^--N RAS. Therefore, higher NO₃^--N levels that may occur in RAS will not adversely or beneficially impact geosmin-related off-flavor problems.     

Effect of nitrite on larval development of giant river prawn Macrobrachium rosenbergii

The effects of ambient nitrite concentrations on larval development of giant river prawn Macrobrachium rosenbergii were evaluated. The trials were conducted in two phases: phase 1, larvae from stages I through VIII and phase 2, larvae from stage VIII until post-larvae. In both phases larvae were kept in water with nitrite (NO₂-N) concentrations of 0, 2, 4, 8 and 16 mg/L. Oxygen consumption was analyzed for larvae in stage II at nitrite concentrations of 0, 4, and 8 mg/L. Survival, weight gain, larval stage index and metamorphosis rate decreased linearly with increasing ambient nitrite concentration. However, there was no significant difference between larvae subjected to 0 and 2 mg/L NO₂-N. In phase 1, there was total mortality at 16 mg/L NO₂-N, while in phase 2 larval development stopped at stage X in this treatment. The oxygen consumption in stage II increased significantly at NO₂-N concentration from 0 to 4 mg/L, but there was no difference between 4 and 8 mg/L NO₂-N. In conclusion, increasing ambient nitrite up to 16 mg/L NO₂-N delays larval development, reduces larval growth rate and causes mortality, whereas no significant effect occurs for levels below 2 mg/L NO₂-N. However, the establishment of a general safe level of nitrite to M. rosenbergii hatchery may be difficult due to the great variability in larvae individual sensitivity.