Fish welfare in aquaculture: From physiology to molecular activities and new tools for study innovative diets, social and spatial stress

Guaranteeing a high quality of life for animals has recently become a matter of increasing concern. Welfare assessment has been well-developed for terrestrial species, mainly for those kept in captivity, but the current state of the art is less well-characterized for aquatic animals. The classical methodologies utilised to date, such as the kind of behavioural observation widely used for terrestrial animals, are not appropriate for improving our knowledge of the well-being of aquatic animals if used alone, mainly due to the large number of species and the difficulty of obtaining comparative results among the different taxa of interest. Among different approaches, the evaluation of internal responses inside organisms can be carried out using different physiological and biochemical tools. This thesis presents methodologies and results of studies aimed at validating physiological and immunity parameters as markers of stress in the evaluation of fish welfare, with a particular focus on two important species in aquaculture, Sparus aurata and Dicentrarchus labrax. Fish were exposed to different conditions, and their welfare status was evaluated. An approach based on physiological markers was introduced to investigate the effects of the surgical implantation of electronic tags to provide telemetry for aquaculture study purposes. Indeed, the use of telemetry to study aquatic organisms has developed rapidly and its utilization needs to be better understood. Nutrition and food quality are further critical aspects for farmed animals. Indeed, aquaculture, both conventional and organic, has increased widely in recent years and has attracted the attention of various stakeholders. Physiological stress indicators, growth performance, and swimming activity data obtained by acoustic transmitters are good indicators for welfare assessment, and here they have been used to evaluate the effect of different aquaculture methodologies, in particular on fish fed with different diets. In addition, social stress and territoriality are relevant factors to evaluate for gregarious species that may have consequences on animals farmed in captivity conditions. These aspects may impair the ability of fish to respond to various stimuli, such as pathogens and environmental variations, with negative influences. In this thesis, we evaluate the effects of social stress on gilthead bream through behavioural observation supported by the evaluation of physiological and immunological-cellular parameters, such as cortisol, glucose, lactate, osmolarity, and phagocytosis.