Confirmation of catfish, Ictalurus punctatus (Rafinesque), mortality from Microcystis toxins

Unexplained deaths of pond-grown catfish have occurred for many years. At least some of these mortalities could be from cyanobacteria toxins ingested during feeding on floating diets or passively assimilated through gills during breathing. Recently we were able to document algal production and subsequent ingestion of these toxicants by catfish during a mortality event. The causative organism, Microcystis aeruginosa, was the dominant species within the phytoplankton community during the cooler autumn-winter season. Pond conditions included a drop in water temperature by c . 5 °C during the 10 days preceding the fish mortalities. Microcystin-LR, a hepatotoxin produced by Microcystis , was detected in water samples and in catfish liver tissue. Fish exposed to pond water containing this toxic bloom were killed within 24 h. Necropsy of fish revealed congested liver and spleen tissues. The combination of clinical signs, detection of microcystin LR in water and in liver, and death of fish exposed to pond water supports the diagnosis of microcystin toxicosis. More research is needed to identify specific environmental conditions initiating toxin production to model and predict occurrence of these toxic algal blooms.     

三峡水库小江回水区水华期间水环境因子对微囊藻丰度的影响

小江是三峡库区北岸流域面积最大的一条支流，其回水区富营养化备受关注。2016年4月下旬至5月，中旬小江回水区高阳断面和双江断面爆发了水华。以高阳断面和双江断面为监测区域，采用冗余分析方法，探究水华爆发期微囊藻丰度与水环境因子的关系，以期找出水华应急阶段关键水环境因子，为小江回水区微囊藻水华预警监测和防控提供科学依据。结果表明，随着水深逐渐增加，微囊藻的丰度逐渐减少，高阳断面上表层（水下0.5 m）、中层（1/2水深）、底层（底部以上0.5 m）微囊藻丰度为2467.67×104个/L、792.58×104 个/L和729.72×104 个/L；双江断面表、中、底层分别为1337.57×104个/L、298.75×104个/L和108.79×104个/L；高阳断面微囊藻丰度明显高于双江断面。高阳断面的水温、溶解氧和高锰酸盐指数明显高于双江断面，其他水环境指标的差异性不显著。冗余分析Monte Carlo检验结果显示，高阳断面溶解氧（P=0.045）与微囊藻丰度呈显著正相关，电导率（P=0.047）与微囊藻丰度呈显著负相关，双江断面水温（P=0.002）与微囊藻丰度呈极显著正相关，透明度与微囊藻丰度呈显著负相关（P=0.011）。     

Evidence of rapid transfer and bioaccumulation of Microcystin‐LR poses potential risk to freshwater prawn Macrobrachium rosenbergii (de Man)

Microcystins accumulate in aquatic organisms and can be transferred to higher trophic levels, eventually affecting vector animals and consumers. We examined three levels of an aquatic food chain (Microcystis aeruginosa, Daphnia magna and Macrobrachium rosenbergii) to identify the transfer efficiency and risk of microcystin on prawns. Samples were analysed using ultra performance liquid chromatography‐mass spectrometry (MS)/MS and microcystin‐LR (MC‐LR) distributions in prawn tissues were studied. The results showed that prawns accumulate MC‐LR both directly from M. aeruginosa and indirectly through D. magna which was pre‐exposed to M. aeruginosa. MC‐LR was detected in the gills, digestive tracts and hepatopancreas of the prawns 2 h after exposure. MC‐LR accumulated in prawns to 0.49 ± 0.04 μg g^?1 dry weight in hepatopancreas within 24 h, while it was not detected in muscle samples, and rarely appeared in blood samples in such a short period. Although MC‐LR was not detected in muscle, the head including hepatopancreas of the prawns accumulated troublesome amounts of MC‐LR. These results demonstrate that microcystis blooms in prawn farming potentially pose a risk to human consumers, although prawns may be exposed to the bloom for a very short time, hence regular monitoring of blue green algae population is recommended.     

Biochemical parameters of blood plasma and content of microcystins in tissues of common carp (Cyprinus carpio L.) from a hypertrophic pond with cyanobacterial water bloom

The aim of this study was to evaluate the dynamics of the blood plasma parameters and the content of microcystins in the tissues of common carp ( Cyprinus carpio L.) in relation to the toxic cyanobacterial water bloom. Fish (average body mass 2176±697 g) in the hypertrophic pond were exposed to natural water bloom (dominated by Planktothrix agardhii, Pseudanabaena limnetica and Limnothrix redekei ), which contained microcystins (concentration in biomass 20–181 μg g⁻¹ dry wt, concentration in water 0.3–9.5 μg L⁻¹). Biochemical parameters in fish blood plasma were analysed in 89 fish at 14-day intervals during the whole season (nine sampling periods). Our results demonstrated high variability and fluctuations in the investigated parameters. The content of microcystins and density of cyanobacterial cells correlated with some haematological indices as lipase, alanine–aminotransferase, albumin, magnesium and chlorides. The concentrations of microcystins in the muscle and liver of the fish (determined by high-performance liquid chromatography with mass spectrometer) were below the limit of detection during the monitored period [0.31 ng g⁻¹ fresh weight (f.w.) for the liver and 0.13 ng g⁻¹ f.w. for muscle]. Our study demonstrates that although known cyanobacterial toxin microcystins were not detected in the fish tissues, several biochemical parameters important for the fish physiology were modulated by natural cyanobacterial bloom.     

太湖微囊藻毒素在罗非鱼体内的累积及生物降解的初步研究

为了解蓝藻水华期间微囊藻毒素在罗非鱼体内的分布及累积传递过程，2008年6月至8月采集了高密度蓝藻池塘及太湖网箱内的鱼样及水样，用ELISA法对鱼样和水样进行微囊藻毒素MC-LR含量的检测。结果表明：池塘水体微囊藻毒素MC-LR含量变化范围在0.123～0.514ug/L间，MC-LR含量随着藻密度的下降而降低，对照组水体MC-LR浓度显著高于实验组MC-LR含量。池塘鱼体肌肉组织微囊藻毒素MC-LR累积含量在1.194～3.615ng/g间，肝脏组织微囊藻毒素MC-LR累积含量显著高于肌肉组织。将池塘与网箱罗非鱼转至无微囊藻水体中暂养，跟踪检测MC-LR含量变化，池塘和网箱鱼体肌肉组织微囊藻毒素MC-LR含量均低于人体每日可耐受摄入量，而肝脏组织藻毒素MC-LR含量则分别需要经过10～20天自然生物降解后降低至安全摄入量之下。并讨论了微囊藻毒素在鱼体内的组织分布与食物链中的累积传递。     

金鱼藻和狐尾藻对铜绿微囊藻生长及藻毒素释放的影响

通过加入金鱼藻(Ceratophyllum)、狐尾藻(Myriophyllum)与铜绿微囊藻(Microcystis aeruginosa)共同培养的实验方式,测定其过程中藻密度、总氮和总磷、藻毒素含量的变化,研究金鱼藻、狐尾藻对微囊藻生长及藻毒素释放的影响。结果表明,金鱼藻、狐尾藻不仅能很好地抑制铜绿微囊藻的生长,吸收水中的氮磷元素,还能在一定程度上抑制微囊藻毒素的释放。其中狐尾藻对铜绿微囊藻密度的抑制率能高达91.19%,对氮和磷的吸附率分别为66.84%和53.75%,对藻毒素MC-LR的抑制率达到44.23%。     

尼罗与奥利亚罗非鱼对池塘蓝藻水华及水质影响的研究

利用尼罗罗非鱼和奥利亚罗非鱼进行了池塘抑藻试验，采用血球计数板测定水体中的微囊藻密度，并对水体理化性质进行了检测分析。试验结果表明，罗非鱼能有效消减水体中蓝藻生物量，降低水体藻毒素浓度，并对水体TN、TP产生一定影响。其中奥利亚罗非鱼试验组蓝藻初始密度为1．53-108cells／L，下降至0．86-108eells／L，降低43．79％；尼罗罗非鱼组蓝藻初始密度为1．54-108cells／L，下降至O．51×108cells，L，降低66．88％。水体总磷含量无显著变化，总氮含量有所下降，水体微囊藻毒素MC—LR含量随着蓝藻密度的下降而降低，并讨论了尼罗与奥利亚罗非鱼摄食抑制蓝藻的摄食抑制及其对水质的影响。     

Changes in the nutritional parameters of muscles of the common carp (Cyprinus carpio) and the silver carp (Hypophthalmichthys molitrix) following environmental exposure to cyanobacterial water bloom

The present study evaluated the effect of naturally developing cyanobacteria on the composition of muscles of two commercially important freshwater fish species. Fish were exposed to cyanobacterial biomass including Microcystis aeruginosa and Microcystis ichthyoblabe for 4 weeks. Then, they were transferred to dechlorinated potable water without any cyanobacteria for another 4-week period, thus modelling their preparation for consumers. Samples of muscles were collected every week during exposure and subsequent stay in dechlorinated potable water. The cyanobacterial water bloom of 3.9–6 × 10⁵ cells mL⁻¹ (133–383 μg g⁻¹ of total MC DW) induced statistically significant effects only in the content of fatty acids ( P <0.05; P <0.01) in the common carp ( Cyprinus carpio ), while all studied parameters including the content of dry matter and fat ( P <0.01), proteins ( P <0.05), fatty acid composition ( P <0.05; P <0.01) and some amino acids ( P <0.05) were affected in the silver carp ( Hypophthalmichthys molitrix ). This study has shown that cyanobacteria in the environment of commercially produced fish may decrease the dietetic value of fish muscles.     

三类分子探针对常见赤潮生物的检测

集中使用寡核苷酸、肽核酸和细胞凝素3类探针对来自东海和厦门海域的现场赤潮样品进行了检测,尝试鉴定识别自然水样中有害的赤潮原因种塔玛亚历山大藻,微小原甲藻和纤小裸甲藻,建立和优化了这些探针的检测方法和样品处理程序.结果表明,在东海和厦门海域的赤潮样品中均成功地检出了塔玛亚历山大藻的分布情况,各探针的检测效率为DBA>Tama28S>Tama5S;在东海和厦门海域的赤潮样品中,也成功地检测出了微小原甲藻,各探针的检测效率为:ConA>PM18S02>PM28S02;在厦门海域的赤潮水样中检出了纤小裸甲藻,各探针的检测效率为:WGA>PNATP28S01>TP18S02>TP28S01.各探针检测结果与相关文献的报道吻合较好.比较这3类探针的特异性,其中以PNA探针为最好,其次为DNA;lectin探针的特异性相对较弱.     

浅议养鳗池中的微囊藻

养鳗池中常易引起微囊藻“水华”,国内外一些养鳗技术资料对此藻类的存在和大量繁殖持肯定态度,认为有利于增氧,除氨氮,笔者则认为,微囊藻产生的毒素对鱼类有害,鳗池中培养绿藻（如小球藻等）同样能起到增氧,除氧作用,我国的传统养鱼经验之一,掌握池水的“肥、嫩、爽”也适用于养鳗生产。