European seabass Dicentrarchus labrax is an economically important species in Mediterranean aquaculture (Cardia and Lovatelli, 2007), with the top producers of this fish species located in Turkey and Greece followed by Egypt and Spain (FAO/GLOBEFISH, 2013). The production of European seabass increased to 128.105 tons in 2013 (FEAP, 2014), which does not account for the contribution from Egypt. Portion-sized fish are mainly produced in the Mediterranean Sea (Cardia and Lovatelli, 2007; Monfort, 2007), with a small fraction of the Turkish production originating from the Black Sea (FAO/GLOBEFISH, 2013). Infectious diseases threaten aquaculture industries not only via direct financial costs related to biomass losses but also via indirect costs related to disease management practices and depreciation of product value. Among the potential disease agents, bacterial pathogens are the most frequently encountered (Lafferty et al., 2015; Meyer, 1991). In the Mediterranean Sea, the

Effective analysis of pathogens causing human and veterinary diseases demands rapid, specific and sensitive detection methods which can be applied in research laboratory setups and in field for routine diagnosis. Paper lateral flow biosensors (LFBs) have been established as attractive tools for such analytical applications. In the present study a prototype LFB was designed for whole particles (virions) detection of nodavirus or fish nervous necrosis virus. Nodavirus is an important threat in the aquaculture industry, causing severe economic losses and environmental problems. The LFB was based on polyclonal antibodies conjugated on gold nanoparticles for signal visualization. Brain and retinas from fish samples were homogenized, centrifuged and the supernatant was directly applied on the LFB. formation of a red test line was indicative of nodavirus virions presence. nodavirus visual detection was completed in short time (30 min). Key factors of the LFB development influencing the assays' detection limit were characterized and the optimum parameters were determined, enabling increased efficiency, excluding non-specific interactions. Therefore, the proposed LFB assay consists a robust, simple, low cost and accurate method for detection of nodavirus virions in fish samples. The proposed biosensor is ideal for development of a commercial kit to be used on aquaculture facilities by fish farmers. It is anticipated that disease monitoring and environmental safety will benefit from the simplification of time consuming and costly procedures.Aquaculture is essential to cover fish-product demands, providing seafood in high quantities, and covering more than the half amount of fish consumed worldwide. This fact drives a strong demand for high production efficiency in aquaculture industry in order to cover the feeding needs of the world's growing population, in the middle of an increasing environmental crisis 1,2 . As a result, the aquaculture industry has continuously increased profits in a high rate. However, outbreaks of diseases caused by infectious agents are significantly restricting intensified aquaculture. According to literature 3 , 22.6% of all disease outbreaks are caused by viruses. Among these, viral nervous necrosis (VNN), also named vacuolating encephalopathy and retinopathy or encephalomyelitis, is a devastating disease, which induces cell necrosis accompanied by vacuolation in fish retina and brain. Its clinical symptoms include changes in skin color with abnormal swimming, low feed ingestion and altered buoyancy in affected fish. The disease is caused by nervous necrosis virus (NNV) or nodavirus, affecting more than 30 different fish species, worldwide. VNN causes high mortalities (80-100% in several species e.g. European sea bass), emerging as a major problem especially in the Mediterranean area, since it cannot be prevented by vaccination or effective treatment 4-6 .Fish nervous necrosis virus (belonging to Betanodavirus genus and Nodaviridae family) is icosahedral, and non-enveloped (∼25 nm in diameter). I...