Fish health management in Italian mariculture: perspectives on innovative solutions for bacterial diseases control

This doctoral thesis aimed to enhance fish health management in Mediterranean aquaculture by identifying relevant bacterial pathogens circulating in marine farming systems and developing sustainable biosecurity strategies for disease prevention and control. Over a three-year period, integrated laboratory and field investigations were conducted to contextualize bacterial diseases within Mediterranean mariculture and detect established and emerging pathogens. Pathogen-oriented research was complemented by parallel investigations on biofilm dynamics and probiotic applications, improving understanding of bacterial persistence mechanisms and supporting environmentally sustainable disease control strategies. The research activities were organized into three thematic areas: health surveillance, biofilm investigation, and probiotic applications. Surveillance studies, conducted within an NRRP project, monitored bacterial communities in fish, molluscs, and surrounding environments at floating cage farms in three Italian regions. Sampling of approximately 1,000 fish and 200 molluscs revealed ecological interactions between farmed organisms and environmental microbiota, highlighting the importance of ecosystem-based disease prevention. During these activities, relevant and emerging Mediterranean pathogens were isolated and characterized, including Aeromonas veronii, Piscirickettsia salmonis, and Lactococcus garvieae. Biofilm-related research included in vitro evaluation of the biofilm-forming capacity of selected pathogens, seasonal analyses of microbial exchange between fish and the farming environment, and field assessments of biofilm development in recirculating aquaculture systems. Additional collaborative studies developed laboratory protocols to test essential oils as potential biofilm control agents. Finally, field and experimental trials evaluated probiotics as sustainable alternatives to antibiotics in aquaculture. An in vivo trial under controlled conditions demonstrated increased resistance of European seabass to Vibrio harveyi following administration of Bacillus velezensis D-18, highlighting its potential as an effective probiotic to enhance disease resistance in intensive seabass farming. Overall, this thesis advances Mediterranean fish health management by documenting emerging pathogens, clarifying the role of biofilms in disease persistence, and supporting probiotics as tools to reduce bacterial disease impact and antimicrobial dependence.