Evidence of potential vertical transmission of tilapia lake virus

Tilapia lake virus disease (TiLVD) is an emerging viral disease in tilapia with worldwide distribution. Although the horizontal transmission of TiLV has been demonstrated through the cohabitation of infected fish with susceptible fish, no direct experiment showed the potential of vertical transmission from broodstock to progeny. In this study, natural outbreaks of TiLV in broodstock and fry in two tilapia hatcheries were confirmed. The TiLV genomic RNA was detected in liver and reproductive organs of infected broodstock, while infective virus was isolated in susceptible cell line. In situ hybridization assay confirmed the presence of TiLV in the ovary and testis of naturally infected fish and experimentally challenged fish. Moreover, early detection of TiLV in 2‐day‐old fry and the presence of TiLV genomic RNA and viable virus in the testis and ovary suggested the possible transfer of this virus from infected broodstock to progenies. As infective virus was present in gonads and fry in natural outbreak and experimental fish, the importance of biosecurity and prevention of the virus to establish in the hatchery should be emphasized. Hence, the development of TiLV‐free broodstock and the maintenance of high biosecurity standards in the hatcheries are essential for any attempt of virus eradication.     

Virucidal effects of common disinfectants against tilapia lake virus

Tilapia lake virus (TiLV) is an emerging virus associated with high fish mortality and economic losses. This study investigates the virucidal effects of the following disinfectants (active ingredients) on TiLV: 2.5 ppm iodine, 10 ppm sodium hypochlorite (NaOCl), 300 ppm hydrogen peroxide (H₂O₂), 80 ppm formalin and 5,000 ppm (0.5%) Virkon^®. Factors that affect the disinfectants’ efficacy, including temperature, contact time and soiling (organic matter) interference, were examined under conditions mimicking natural aquaculture practices. TiLV inactivation of higher than 5 log₁₀ TCID₅₀ ml^?1 was achieved after 10 min and at 28°C for all disinfectants except formalin; similar inactivation levels were reached by NaOCl and Virkon^® at 10 min and 4°C. Extended exposure to formalin from 10 to 60 min at 28°C rendered more than 5 log₁₀ inactivation. Increasing synthetic organic matter in the water to mimic soiling interference reduced the efficacy of NaOCl, iodine and H₂O₂ when tested at 10 min and 28°C; however, Virkon^® still achieved more than 5 log₁₀ inactivation. This study demonstrates that most common disinfectants effectively reduced viral loads to minimum levels. To limit the spread of TiLV in aquaculture farms and related facilities, the appropriate use of such disinfectants should therefore be promoted and implemented.     

Cage fish culture in Lake Victoria: A boon or a disaster in waiting?

Fish catches in Lake Victoria have been on the decline while demand for fish has been increasing. Cage culture with >3,000 cages, over 3 million tilapias and valued at US$ 12 million is trying to fill the gap. This study reviews the development of cages and the need to develop a decision support tool for effective management. Existing literature and data on fisheries and cage culture held by the Kenya Marine and Fisheries Research Institute (KMFRI) were used in the analysis. Cage culture is a promising venture that may increase productivity, offer employment and enhance economic well‐being. However, site suitability for the installation of cages is poorly regulated with most developments (>45%) located within 200 m of the shoreline that are breeding grounds of fish and conflict with other lake users. Waste feed increases eutrophication, and enhances growth of algae and water hyacinth in the lake. Recent isolated fish kills were attributed to low dissolved oxygen concentrations (<0.64 mg/L), and an increasing occurrence of fish disease are signs of poor management practices among cage farmers. Cage culture may turn into an environmental disaster if not managed well, and there is need for robust policies and increased awareness to reduce environmental impacts.     

Fatty Acid Profiles and Lipid Oxidation Status of Sun Dried,Deep Fried,and Smoked Sardine (Rastrineobola argentea) from Lake Victoria,Tanzania

Freshwater fishes contain long chain omega-3 and omega-6 polyunsaturated fatty acids (PUFAs) of highest nutritional value. PUFAs in fish are susceptible to oxidative damage during processing and subsequent storage. Sardines (Rastrineobola argentea) are an important fish species of Lake Victoria, constituting 72.3% of the total landings by weight on the Tanzanian side of the lake. Fatty acid profiles and lipid oxidation status of sun-dried, deep-fried, and smoked sardines were investigated. Lipid oxidation was assessed by peroxide value, thiobarbituric acid reactive substances (TBARS), and free fatty acids. Fatty acids were analyzed by gas chromatography with flame ionization detector. The three omega-3 PUFAs: docosahexaenoic acid (C22:6n-3), docosapentaenoic acid (C22:5n-3), and eicosapentaenoic acid (C20: 5n-3) contributed 57–60, 63, and 38% of PUFAs in sun-dried, smoked, and deep-fried sardines, respectively. Lipid oxidation reactions were more pronounced in sardines dried on sand and rocks, with TBARS values 97.87 and 84.18 µmolMDA/kg, respectively. The polyene index was significantly lower (p < 0.05) in deep-fried sardines, indicating lower retention of PUFAs in the product. Lake Victoria sardines are a rich source of omega-3 PUFAs. PUFAs in sun-dried sardines are prone to oxidative damage. Smoking resulted in relatively higher retention of omega-3 fatty acids in products.     

湖泊生态系统稳态转换驱动因子判定方法研究进展

湖泊生态系统会在长期的人为胁迫和短期的强扰动下发生稳态转换,灾变性稳态转换将会导致湖泊水环境在短时间内急剧恶化,进而延缓和加大治理的进程及成本。探求浅水湖泊稳态转换驱动因子是科学合理确定湖泊管理策略的关键所在,现有的驱动因子判定方法主要有实验观测、统计分析和模型模拟。实验观测缺乏对生态系统整体的判断,仅采用观测数据并不能得出导致稳态转换确切的原因和效应;统计分析难以对未来作出预警;模型模拟可有效规避上述2种方法存在的问题,特别是机理模型是今后分析稳态转换的主要方法。有必要加强统计分析与模型模拟的结合、生态模型与传统水质水动力模型耦合等方面的研究工作。     

白洋淀浮游甲壳动物的生物多样性研究

基于2006年4月至2006年12月对白洋淀浮游甲壳动物进行采样调查,分析了白洋淀浮游甲壳动物的群落结构及多样性。本次调查共记录到浮游甲壳动物34种,隶属于9科19属,其中枝角类（Cladocera）19种,桡足类（Copepoda）16种。物种多样性季节性明显：枝角类优势种在春、夏和秋冬季依次为微型裸腹溞（Moina micrura）、长额象鼻溞（Bosmina longirostris）、长肢秀体溞（Diaphanosoma leuch）;而桡足类优势种在冬春季为英勇剑水蚤（Cyclopidae strenuus）,在夏秋季为锯缘真剑水蚤（Eucyclopinae macruroides）和台湾温剑水蚤（Thermocyclops tsihokurnsis）。物种多样性春秋季较高,夏季和冬季较低。浮游甲壳类个体密度以春季最高,冬季最低。根据生物多样性指数综合判定白洋淀的水质为中营养化水平。     

2001-2005年松花湖水质评价

为了了解松花湖近几年水质状况,基于2001～2005年松花湖水质监测数据,以单因子评价法,确定主要污染指标.采取综合污染指数法,对松花湖水质进行评价.结果表明,溶解氧全湖年均值7.604mg/L,符合国家Ⅱ类水体标准.丰满断面石油类污染最重,5年超标率为5.0%;各断面除小荒地高锰酸盐指数未超标外,其余断面均超过国家标准;总氮各断面均超过国家标准.松花湖5个断面水质污染程度比较,污染最严重的是辉发河口,综合污染指数7.69,污染负荷比为28.01;第2位是桦树林,综合污染指数6.54,污染负荷比为23.91;第3位是小荒地、沙石浒和丰满,综合污染指数均为4.45,污染负荷比分别为15.77、15.77和为16.28.可见松花湖水体的主要污染指标为总磷、总氮和高锰酸盐指数,松花湖的大部分水体的水质处于中度污染状态.     

城市湖泊中邻苯二甲酸酯(PAEs)类物质的组成及其分布特征

利用GC-MS检测长春市不同位置的4个城市湖泊表层水体中8种邻苯二甲酸酯(PAEs)的浓度。结果表明:4个湖泊表层水体中PAEs总浓度(∑8PAEs)变化范围为3.02~13.03ng/mL;不同城市湖泊夏季的表层水体中的∑8PAEs含量具有一定差异性,整体表现为北湖最高,南湖和雁鸣湖其次,八一水库最低;∑8PAEs与溶解性有机物浓度(DOC)及总悬浮物浓度(TSM)没有相关性。邻苯二甲酸二甲酯(DMP)、邻苯二甲酸二乙酯(DEP)、邻苯二甲酸二丁酯(DBP)、邻苯二甲酸二(2-乙基)己酯(DEHP)和邻苯二甲酸二异癸酯(DIDP)广泛存在于4个湖泊水体中,5~7月的平均浓度范围依次为:0.04~0.11ng/mL、0.08~1.15ng/mL、1.20~4.30ng/mL、2.86~4.52ng/mL和0.10~0.31ng/mL,而邻苯二甲酸二辛酯(DOP)、邻苯二甲酸二异壬酯(DINP)和邻苯二甲酸丁酯苄酯(BBP)仅在南湖水体中被检测到。根据《地表水环境质量标准》(GB3838-2002)要求,南湖和北湖夏季水体DBP和DEHP浓度均达标,雁鸣湖的DBP浓度超标,八一水库DBP和DEHP浓度均超标。本研究中的4个城市湖泊表层水体中PAEs的浓度高于目前报道的其他地区地表水中PAEs的浓度。     

云南高原湖库浮游细菌的生态分布及其影响因素

2009年秋季,对我国西南云贵高原8个处于不同营养水平的湖泊和水库的浮游细菌进行了调查,分析了浮游细菌的分布特征及其与温度、总氮（TN）、总磷（TP）、正磷酸盐（PO4-P）、氨氮（NH4-N）、硝氮（NO3-N）、化学需氧量（CODMn）和叶绿素a（Chl.a）的相关性。结果表明,8个湖库的浮游细菌数量存在明显差异,异龙湖最高,平均值为5.66×109个/L,阳宗海最低,平均值为2.25×109个/L,从大到小依次为：异龙湖〉草甸海〉松花坝水库〉白沙河水库〉月湖〉松茂水库〉石龙坝〉阳宗海。对阳宗海4个点     

人工湖泊滴水湖水质演变趋势及富营养化分析

对上海临港新城滴水湖自建成以来的水质指标进行为期6年的监测.结果表明,湖区自2004年蓄水以来,水体盐度已由3逐渐下降到2010年的1左右;N/P也呈现逐年下降的趋势,其中磷是滴水湖的营养限制元素;湖区总体水质基本维持在地表水Ⅳ～Ⅴ类,影响水质的主要污染物为CODMn 、Tp、TN和BOD.对湖区富营养化分析的结果表明,其富营养化程度变化趋势与水体中叶绿素a含量的变化基本一致,TP是影响其叶绿素a含量和水体富营养化程度的主要指标,且在夏秋季节容易出现富营养化指数上升的现象.