Towards precision fish farming and low carbon productions in aquaculture: new tools and technologies for a more sustainable, resilient and circular fish farming

The exponential growth of aquaculture over the past two decades has generated both optimism and concern among scientists and policy analysts, particularly regarding environmental sustainability. While aquaculture is acknowledged as one of the least impactful forms of animal production, with minimal use of natural resources, chemicals, and antibiotics, persistent environmental challenges demand attention. This thesis addresses a fundamental question: how can we minimise the environmental impact of aquaculture production? A multidisciplinary examination of the entire aquaculture value chain identified critical points where sustainability challenges are most apparent and can be targeted. A recurring theme throughout the thesis revolves around the exploration of alternative ingredients to marine and plant resources, particularly those derived from industrial by–products, such as single–cell proteins and oil–rich microalgae, in alignment with the principles of a circular economy. The initial study showcased the potential of microalgae, specifically Nannochloropsis spp. and Spirulina spp., produced by converting waste outputs from a geothermal plant, to replace traditional encapsulated fish oil in the diet of European seabass larvae. This shift not only reduced pressure on wild resources but also allowed for the valorisation of waste streams and decreased downstream costs associated with industrial waste disposal. Furthermore, larvae fed microalgae diets exhibited a favourable long–chain polyunsaturated fatty acids (LC–PUFAs) profile, with notable levels of docosahexaenoic acid (DHA), and lower catalase activity, indicating potential antioxidant effects. In contrast, the second study revealed that Corynebacterium glutamicum cell mass, a by–product of industrial amino acid production with high protein content, is not a suitable substitute for fishmeal and soybean meal in the diet of flathead grey mullet. The investigation, encompassing key performance indicators and sophisticated variables like metabolic blood parameters, digestive enzyme activities, and gut microbiota, hypothesised that the species' digestive system organisation led to incomplete utilisation of the ingredient due to poor lysis of cell–wall components. Despite unexpected outcomes, these trials contribute theoretical foundations for the advancement of sustainable aquafeed formulations. Transitioning from production to commercialisation, additional environmental challenges were identified, with over 35 % of global fish production wasted or lost due to incorrect storage or problems at the supply chain. The third study introduced a novel, rapid, and non–destructive method for fish freshness evaluation at the commercialisation level. This involved a device with a vector network analyser interfaced with an open coaxial probe, placed in contact with the fish eye, leveraging dielectric properties. The integration with multivariate analysis facilitated the creation of predictive models for storage time and demerit scores of fish spoilage, offering high sensitivity. This innovative approach is poised to assist producers and retailers in the busy commercial setting, addressing a crucial aspect of environmental sustainability in aquaculture.