engleski

Impact of Viral Encephalopathy and Retinopathy (VER) introduction to Croatian marine farms

Since the first outbreak of viral encephalopathy and retinopathy on two Croatian marine farms in 1995, losses caused by this devastating disease have not been recorded. During the summer of 2014, outbreaks of the disease characterized by abnormal swimming behaviour in European sea bass (Dicentrarchus labrax) were notified from five different farms along the coast. In all cases infected fry was imported from the same hatchery and the outbreaks started a week or a month and half following introduction of fry to farm cages. The sea temperature during outbreaks was ranging from 21 to 24oC. Affected fish from all farms were showing similar symptoms ; dark pigmentation, emaciation, hemorrhagic lesions on the jaws, eye opacity, skin lesions and congestion and haemorrhages on the brain meninges. Mortality rate was very high. Samples of fish were submitted to the laboratory examination and virological examination of the brain homogenate on the SSN-1 cell culture resulted with CPE. Real time RT-qPCR confirmed infection with Noda virus in all cases. Two partial fragments within RNA 1 and RNA 2 of each isolate were amplified and sequenced and genetic characterization was performed. Impact of the infection was studied on the heavily infected farm with recorded advanced symptoms and high mortalities. Samples of all categories of the sea bass and sea bream (Sparus aurata) were collected three weeks after the first detection of the virus. Feral fish swimming around the cages on the infected farm including mullet (Mugil cephalus), salema (Sarpa salpa), bogue (Boops boops) and mussel (Mytilus galloprovincialis) from the cage installation were also collected. All samples were analyzed for the presence of beta noda virus by cell culture technique and RT-qPCR. It was demonstrated that virus has spread only to the older categories of sea bass where clinical symptoms were observed and low mortalities were recorded (up to 5%) compared to yearling category which suffered mortalities from 20 to 50 %.

VER; Nodavirus; European sea bass; Croatia

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