Aquaculture production: current limits and contribution to innovation on fish health management

The general objective of this thesis was to assess the main threats, in terms of diseases, disorders and pollutants, which occur in the breeding of some fish species, both marine and freshwater, and provide an innovative contribution on the health management of farmed fish through the use of immunostimulant food additives and the application of nanomaterials for water treatment. Finfish aquaculture production has seen rapid growth in terms of both production volume and economic performance over the past decades. Aquaculture is today a key supplier of seafood. As the scale of production increases, the industry is likely to face emerging biological, economic and social challenges that can affect the ability to maintain ethically healthy, productive and eco-friendly fish production. It is therefore important that the industry aspires to monitor and control the effects of these challenges to avoid also increasing potential problems during production upscaling. In this perspective, a fish-health monitoring survey was conducted on gilthead sea bream (Sparus aurata) reared in an intensive Italian fish farm and on common carp (Cyprinus carpio) and pike perch (Sander lucioperca) produced in a semi-intensive Croatian fish farm, each lasting six months. The purpose of these activities was to detect the main problems afflicting the two companies under study. The results of the survey showed that infectious diseases represent the main threat in both farms. In particular, Nodavirus and Vibrio sp. represented the main causes of mortality and heavy economic losses in gilthead sea bream farming; parasites such as Ichthyophthirius multifilis and Dactylogyrus spp. greatly affected the breeding of common carp with an occurrence frequency of 22.7% and 33.4% respectively. The entry of Mycobacterium marinum caused a mass mortality of pike perch specimens reared in recirculating aquaculture systems. Deformities represented the second threatening factor in both farms, with an onset of 4.5% and 3.01% in gilthead sea bream and common carp, respectively. Finally, pollutant investigations in water samples from the Italian farm were found to comply with the requirements of the legislative decrees concerning "Environmental standards". However, lower concentrations of microplastics, classified as emerging contaminants, were found in the gastrointestinal tract of farmed gilthead sea bream (0.48 items/specimen) and common carp (0.11 items/specimen) than in their wild counterpart. As outbreaks of infectious disease in farmed fish emerged as the main hurdles for the development of aquaculture, and considering the limitations and side effects of several veterinary therapies commonly used in aquaculture, the interest of researchers has shifted to development of alternative strategies, such as immunostimulants, for the prevention and control of infectious diseases. In the present research, we investigated the effects of dietary Imoviral on immune-related gene expression at spleen level in gilthead sea bream infected with Vibrio anguillarum. Fish were fed two diets, with or without Imoviral supplementation. The trial lasted for 4 weeks, then fish were divided into five groups; the second and fourth groups were intra-peritoneally injected with phosphate buffer saline (PBS) while the first and third groups were challenged with a sublethal dose of Vibrio anguillarum. The fifth group was the control group. At 1 h, 24 h, 72 h and 168 h post challenge, immune-related gene expressions were evaluated. The results indicated that administration of Imoviral could significantly improve the immune response in fish fed supplemented diets, confirming the beneficial effects of Imoviral as a natural alternative immunostimulant for gilthead sea bream aquaculture. Pollutants, such as heavy metal or pesticides, in the aquatic environment undoubtedly represent one of the main problems that society faces today, representing also one of the greatest threats for aquaculture production. Therefore, in the last few decades, the development of efficient and ecologically-friendly methods to remove contaminants from water has become of relevant importance. In this context, nanotechnology has gained a lot of attention in recent decades due to the unique physical properties of nanoscale materials, which are particularly efficient in the field of remediation. It is, however, important to verify that the materials used for the remediation of pollution are not themselves another pollutant after being used. In this study, we have investigated the toxicity of photocatalysts molecularly imprinted titanium dioxide (TiO2), also N-doped, for selective removal of the o-phenylphenol (OPP) fungicide from water. The toxicity of the nanoparticles was established by a zebrafish embryo toxicity test, an alternative method of animal test. Zebrafish embryos were exposed to: TiO2 bare, TiO2 sol-gel, molecularly imprinted (MI) MITiO2/o-p.p. and molecularly imprinted MITiO2/o-p.p. N-doped at 0.8%, 1.2% and 4%. Moreover, other larvae were exposed to molecularly imprinted MITiO2/o-p.p. N-doped at 0.8%, 1.2% and 4% with the addition of the OPP fungicide (1x10-4 mg/ml) in the ratio of 1:1. As exposure biomarkers, we evaluated the expression of metallothioneins 1 and Heat Shock Proteins 70 by immunohistochemistry analysis. The results obtained from the toxicity test showed that neither mortality nor sublethal effects were induced by the different nanoparticles tested. The zebrafish exposed to imprinted nanoparticles with OPP fungicide (1:1) died one hour after exposure and therefore the immunohistochemical analysis showed no response to the biomarkers tested.