引起半滑舌鳎(Cynoglossus semilaevis Günther)鱼苗大规模死亡的神经坏死病毒病

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。

Preliminary Study on Massive Mortality of Hatchery-Reared Half-Smooth Tongue Sole, Cynoglossus semilaevis, Associated with Viral Nervous Necrosis

In the years of 2012 and 2013, there was an outbreak of disease and massive death of half-smooth tongue sole (Cynoglossus semilaevis) 15–20 days post-hatching (dph 15–20) in a hatchery of northern China, and the cumulative mortality reached 90%–100% within one week. The outbreak occurred in July and August when the water temperature was 22–24℃. The symptoms included erratic swimming behaviors such as spiraling movement and fast swimming in circles, without hemorrhaging and ulceration on body surfaces. The histopathological examination revealed typical signs of viral nervous necrosis. The nerve cells of brain and retina underwent severe vacuolation and necrosis. RT-PCR with primers of nervous necrosis virus showed positive results in all samples from moribund half-smooth tongue soles. The RT-PCR products were then sequenced and the sequence alignment was carried out with BLAST. It was found that the sequence similarity was above 98% between the nervous necrosis virus in half-smooth tongue sole (CsCN NNV) and five strains of red-spotted grouper nervous necrosis virus (RGNNV). In contrast, the similarities between CsCN NNV and other three genotype strains of NNV:Striped jack nervous necrosis virus (SJNNV),Barfin flounder nervous necrosis virus (BFNNV), andTiger puffer nervous necrosis virus (TPNNV), were only 71%–78%. Therefore, we inferred that CsCN NNV was a new strain with RGNNV genotype. It was the first case of naturally occurred RGNNV infection of half-smooth tongue sole. Our findings provided insights into the epidemic mechanism of RGNNV infection as well as the prevention of viral nervous necrosis in half-smooth tongue sole.