The SEA2LAND project is a 4-year collaborative Innovation Action (IA) funded by the EU in the frame of the Horizon 2020 programme. Based on the circular economy model, SEA2LAND promotes the production of fertilisers in the EU from own raw materials. This solution is expected to reduce the soil nutrient imbalance in Europe. The basis of the project is the regional production of bio-based fertilizers (BBF) by developing dedicated demonstration pilots that can be replicated across Europe, boosting local growth. For the Atlantic area, the Sea2Land project aims at producing BBF’s from the by-products of the aquaculture domain using ThermoMechanoChemical (TMC) fractionation by twin-screw extrusion. TMC process is a continuous process, working at low liquid/solid ratios and able to provide a solid and a liquid fraction. Until now, the processes concerning extrusion/fish/fertilizer had been limited to: a) the mixing of fish with vegetal raw materials by twin-screw extrusion for the production of pellets for the feed industry, b) the pretreatment of lignocellulosic raw materials with enzymes by twin-screw extrusion to initiate the enzymatic hydrolysis, c) the transformation of fish bones and heads by extrusion for the production of gelatins films, and d) the production of organic fertilizers by urea and derivatives. The use of TMC process for fertilizers production is an innovative approach that makes it possible to recover not only products with an agronomic value but also other components such as lipids to reach a ZERO-waste process. TMC process had never been used in the presence of enzymes for the transformation of aquaculture by-products into BBF’s. Retained by-products are heads, fishbones and viscera from Steelhead truit (Oncorhynchus mykiss). The pilot implemented in the Atlantic Area includes the following technological units: (i) Grinding technologies, (ii) TMC fractionation by twin-screw extrusion, (iii) Enzymatic Hydrolysis, (iv) Separation by centrifugation technologies and (v) Concentration technologies. The objectives are the production of 20 kg BBF/week and of 200 kg BBF/week at 2 different pilot scales in optimized operating conditions.