Smith P T
Department of Biology, University of Western Sydney, Campbelltown, NSW, Australia.
Toxicon. 1996 Aug;34(8):857-69. doi: 10.1016/0041-0101(96)00048-7.
Benthic and planktonic blooms of species of Oscillatoriales coincided with mortalities of Penaeus monodon during four episodes at Australian prawn farms. Oscillatoria corakiana was the dominant planktonic species at 65-90,000 cells/ml, but Spirulina sp., Lyngbya sp., Oscillatoria sp. and Nodularia sp. were also identified from the water column, benthic layers or surface mats. The levels and variety of Vibrionaceae in prawn tissue, suggest that mortalities were caused by secondary infections of bacteria. However, experimental results indicate that toxicity of the blooms of Oscillatoriales was the primary cause of disease. Pond water and extracts from a tank culture of benthic Oscillatoriales caused mortalities when injected into P. monodon and P. japonicus. Immersion of artemia in extracts from the tank culture also caused mortalities, with L.D50 values for the supernatant extract of 70 mg/litre for artemia cysts and 50 mg/litre for adult artemia, and LD50 values for the pellet extract of 110 mg/litre for artemia cysts and 200 mg/litre for adult artemia. Experiments with artemia suggested the blooms of Oscillatoriales produced water-soluble, heat-labile toxin/s. Mortalities may have been caused by a neurotoxin because: (a) there was a lack of histopathological evidence of damage to the digestive tracts of prawns during each episode; and (b) artemia cysts immersed in extracts of Oscillatoriales died before they developed digestive tracts. PSP toxin, anatoxin-a, homoanatoxin-a and microcystins were not detected when pond water from a diseased pond was tested. It is proposed that sub-lethal levels of toxin weakened the prawns, causing reduced feeding behaviour and an impaired immune system. As a result, prawns were prone to secondary infection by pathogenic bacteria. Because Oscillatoriales are ubiquitous in prawn farms, the findings have significant implications for the assessment of disease in the prawn farming industry.
在澳大利亚对虾养殖场的四个事件中，颤藻目物种的底栖和浮游水华与斑节对虾的死亡事件同时发生。科拉基颤藻是优势浮游物种，密度为65 - 90,000个细胞/毫升，但也从水柱、底栖层或表面垫层中鉴定出螺旋藻属、鞘丝藻属、颤藻属和节球藻属。对虾组织中弧菌科的水平和种类表明，死亡是由细菌的二次感染引起的。然而，实验结果表明，颤藻目的水华毒性是疾病的主要原因。将患病池塘的池水和底栖颤藻目水槽培养物的提取物注射到斑节对虾和日本对虾体内时，会导致死亡。将卤虫浸泡在水槽培养物的提取物中也会导致死亡，上清液提取物对卤虫卵的半数致死剂量（LD50）值为70毫克/升，对成年卤虫为50毫克/升；沉淀提取物对卤虫卵的LD50值为110毫克/升，对成年卤虫为200毫克/升。对卤虫的实验表明，颤藻目的水华产生了水溶性、热不稳定毒素。死亡可能是由神经毒素引起的，原因如下：(a) 在每个事件中，没有组织病理学证据表明对虾消化道受到损伤；(b) 浸泡在颤藻目提取物中的卤虫卵在发育出消化道之前就死亡了。对患病池塘的池水进行检测时，未检测到麻痹性贝类毒素（PSP毒素）、anatoxin-a、homoanatoxin-a和微囊藻毒素。有人提出，亚致死水平的毒素会削弱对虾的体质，导致摄食行为减少和免疫系统受损。结果，对虾容易受到病原菌的二次感染。由于颤藻目在对虾养殖场中普遍存在，这些发现对虾养殖行业的疾病评估具有重要意义。
