The rapid and intensive growth of aquaculture over the last decade, poses a tremendous challenge to this industry in order to comply with the latest guidelines, established to minimise its negative effects on the environment, animal welfare and public health. Farmed fish welfare has become one of the main priorities towards sustainable aquaculture production with several initiatives launched by the European Union within the framework of the 2030 agenda. It is clear that an unbiased and reliable way to access farmed fish welfare needs to be implemented due to the lack of reliable indicators and standardised methods that are used at present. In this review, we start by addressing the status quo of animal and fish welfare definition in particular, describing the methods and assays currently used to measure it. We then explain why we believe these methods are unreliable and why there is a need to establish new ones that will promote productivity and consumer's acceptance of farmed fish. The establishment of a new type of welfare biomarkers using cutting‐edge technologies like proteomics and other omics technologies is proposed as a solution to this issue. Therefore, we provide a brief description of these new methodologies, describing for each one how they can improve our scientific knowledge and the role they can play in farmed fish welfare biomarker discovery.

Amyloodiniosis represents a major bottleneck for semi-intensive aquaculture production in Southern Europe, causing extremely high mortalities. Amyloodinium ocellatum is a parasitic dinoflagellate that can infest almost all fish, crustacean and bivalves that live within its ecological range. Fish mortalities are usually attributed to anoxia, associated with serious gill hyperplasia, inflammation, haemorrhage and necrosis in heavy infestations; or with osmoregulatory impairment and secondary microbial infections due to severe epithelial damage in mild infestation. However, physiological information about the host responses to A. ocellatum infestation is scarce. In this work, we analysed the proteome of gilthead sea bream (Sparus aurata) plasma and relate it with haematological and immunological indicators, in order to enlighten the different physiological responses when exposed to an A. ocellatum outbreak. Using 2D-DIGE, immunological and haematological analysis and in response to the A. ocellatum contamination we have identified several proteins associated with acute-phase response, inflammation, lipid transport, homoeostasis, and osmoregulation, wound healing, neoplasia and iron transport. Overall, this preliminary study revealed that amyloodiniosis affects some fish functional pathways as revealed by the changes in the plasma proteome of S. aurata, and that the innate immunological system is not activated in the presence of the parasite.

Meagre (Argyrosomus regius) is considered a potential candidate for aquaculture diversification in southern Europe. The main objective of this experiment was to develop a cold storage protocol for meagre semen to facilitate artificial reproduction techniques. Three extenders (non-activating medium, 0.9% NaCl, and 0.9% NaCl with glycine and glucose) in three different sperm:extender dilutions (1:4, 1:9 and 1:19) were tested in a full factorial design. The quality parameters assessed along the storage time were the sperm motility, viable sperm percentage, adenosine triphosphate (ATP) content, and bacterial growth. The 0.9% NaCl and 0.9% NaCl with glycine and glucose extenders and the 1:4 and 1:9 dilutions maintained a higher sperm motility and a higher sperm linearity for a longer period time.Sperm viability was maintained at a higher value over a longer period with the 0.9% NaCl and 0.9% NaCl with glycine and glucose extenders. Sperm motility and viability appeared to be the main parameters showing the loss of semen quality during cold storage. Meagre semen demonstrated an ability to be stored for up to 10 days at 4°C when using 0.9% NaCl in a 1:4 dilution. These results contribute to a better understanding of the causes of fish semen quality deterioration during cold storage.

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