Over the last three decades, the causative agent of viral encephalopathy and retinopathy (VER) disease has become a serious problem of marine finfish aquaculture, and more recently the disease has also been associated with farmed freshwater fish. The virus has been classified as a Betanodavirus within the family Nodaviridae, and the fact that Betanodaviruses are known to affect more than 120 different farmed and wild fish and invertebrate species, highlights the risk that Betanodaviruses pose to global aquaculture production. Betanodaviruses have been clustered into four genotypes, based on the RNA sequence of the T4 variable region of their capsid protein, and are named after the fish species from which they were first derived i.e. Striped Jack nervous necrosis virus (SJNNV), Tiger puffer nervous necrosis virus (TPNNV), Barfin flounder nervous necrosis virus (BFNNV) and Red-spotted grouper nervous necrosis virus (RGNNV), while an additional genotype turbot betanodavirus strain (TNV) has also been proposed. However, these genotypes tend to be associated with a particular water temperature range rather than being species-specific. Larvae and juvenile fish are especially susceptible to VER, with up to 100% mortality resulting in these age groups during disease episodes, with vertical transmission of the virus increasing the disease problem in smaller fish. A number of vaccine preparations have been tested in the laboratory and in the field e.g. inactivated virus, recombinant proteins, virus-like particles and DNA based vaccines, and their efficacy, based on relative percentage survival, has ranged from medium to high levels of protection to little or no protection. Ultimately a combination of effective prophylactic measures, including vaccination, is needed to control VER, and should also target larvae and broodstock stages of production to help the industry deal with the problem of vertical transmission. As yet there are no commercial vaccines for VER and the aquaculture industry eagerly awaits such a product. In this review we provide an overview on the current state of knowledge of the disease, the pathogen, and interactions between betanodavirus and its host, to provide a greater understanding of the multiple factors involved in the disease process. Such knowledge is needed to develop effective methods for controlling VER in the field, to protect the various aquaculture species farmed globally from the different Betanodavirus genotypes to which they are susceptible.

Climate change is expected to have a drastic effect on aquaculture worldwide. As we move forward with the agenda to increase and diversify aquaculture production, rising temperatures will have a progressively relevant impact on fish farming, linked to a multitude of issues associated with fish welfare. Temperature affects the physiology of both fish and pathogens, and has the potential to lead to significant increases in disease outbreaks within aquaculture systems, resulting in severe financial impacts. Significant shifts in future temperature regimes are projected for the Mediterranean Sea. We therefore aim to review and discuss the existing knowledge relating to disease outbreaks in the context of climate change in Mediterranean finfish aquaculture. The objective is to describe the effects of temperature on the physiology of both fish and pathogens, and moreover to list and discuss the principal diseases of the three main fish species farmed in the Mediterranean, namely gilthead seabream (Sparus aurata), European seabass (Dicentrarchus labrax), and meagre (Argyrosomus regius). We will attempt to link the pathology of each disease to a specific temperature range, while discussing potential future disease threats associated with the available climate change trends for the Mediterranean Sea.

To examine the influence of the dietary ratio of (n-3) to (n-6) polyunsaturated fatty acids (PUFAs) on the immune system of Atlantic salmon, Salmo salar L., two dietary trials were carried out in which parr were maintained on diets containing either fish oil [(n-3)/(n-6) PUFA = 5.2] or sunflower oil [(n-3)/(n-6) PUFA = 0.3] and assessed for differences in immunological parameters. There were no significant differences in blood cell counts, differential leucocyte counts or haematocrit values between dietary groups, and while no apparent differences were observed in the non-specific immune parameters measured, there was a significantly higher number of B cells responding to Aeromonas salmonicida, in the kidney and spleen of vaccinated fish maintained on high (n-3)/(n-6) PUFAs diets. There was also a significant difference (P≤ 0.01) between the dietary groups in trial 1 and trial 2 when non-vaccinated fish were challenged with Aeromonas salmonicida and Vibrio anguillarum, respectively, with the (n-6) group succumbing to the bacterium before the (n-3) group. The results suggest that Atlantic salmon fed diets with a low ratio of (n-3)/(n-6) PUFA may be less resistant to infection than those fed diets containing lipid with a high (n-3)/(n-6) PUFA ratio.