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2012和2013年,山东某育苗场15–20日龄的半滑舌鳎(Cynoglossus semilaevis Günther)鱼苗出现暴发性大规模死亡,7 d内死亡率高达90%–100%。本研究调查了疾病的发生情况和临床特征,采集病鱼样品进行了组织病理学检查,并运用RT-PCR方法进行了病原的检测和基因序列分析。结果发现,半滑舌鳎鱼苗一般在7月和8月发病,发病时养殖水温为22–24℃。病鱼游泳行为异常,表现为上下翻游、螺旋性游动、全身大幅度波浪状浮动症状,但病鱼体表无出血和溃疡症状。组织病理检查发现,病鱼脑和视网膜组织出现严重的空泡化及坏死。病鱼样品的RT-PCR检测结果全部呈鱼类神经坏死病毒阳性。对得到的RT-PCR产物测序,进行BLAST比对,发现该病毒与鱼类神经坏死病毒的赤点石斑鱼神经坏死病毒(Red-spotted grouper nervous necrosis virus,RGNNV)基因型的相似性达98%以上,而与鱼类神经坏死病毒的其他3个基因型:黄带拟鲹神经坏死病毒(Striped jack nervous necrosis virus,SJNNV)、红鳍东方鲀神经坏死病毒(Tiger puffer nervous necrosis virus,TPNNV)和条斑星鲽神经坏死病毒(Barfin flounder nervous necrosis virus,BFNNV)的相似性仅为71%–78%。由此可以判定,本研究发现的引起半滑舌鳎鱼苗大规模死亡的神经坏死病毒为RGNNV基因型,半滑舌鳎也是鱼类神经坏死病毒的天然宿主。该发现在半滑舌鳎疾病防治和鱼类神经坏死病毒的流行机制研究方面都具有重要意义。
In 2012 and 2013, 15th-20th-day-old Cynoglossus semilaevis Günther fishes in a nursery in Shandong Province were exposed to large-scale and fatal deaths with 90% -100% mortality within 7 days. This study investigated the occurrence and clinical features of the disease, collected diseased fish samples for histopathological examination and pathogen detection and gene sequence analysis using RT-PCR. The results showed that the half-smooth tongue bream fry generally onset in July and August, when the incidence of breeding water temperature of 22-24 ℃. Diseased fish swim abnormalities, manifested as up and down tour, spiral swimming, the body wavy symptoms of significant fluctuations, but diseased fish body surface without bleeding and ulcer symptoms. Histopathological examination found that disease fish brain and retinal tissue serious vacuolation and necrosis. The results of RT-PCR of diseased fish samples were all positive for fish nervous necrosis virus. The obtained RT-PCR products were sequenced and compared by BLAST. The results showed that the similarity between the virus and the fish necrosis virus necrotic virus (RGNNV) genotype was 98 %, But not with other three genotypes of fish neurovascal necrosis virus: Striped jack nervous necrosis virus (SJNNV), Tiger puffer nervous necrosis virus (TPNNV) And Barfin flounder nervous necrosis virus (BFNNV), the similarity is only 71% -78%. From this, we can conclude that the neurovascular necrosis virus that caused the large-scale death of the half-smooth-headed bonito fry was RGNNV genotype, and the soleus was also the natural host of the fish nervous necrosis virus. This finding is of great importance in the prevention and treatment of halophilagum spp. And the epidemiological mechanism of fish necrosis virus.