The offshore aquaculture project, which was submitted in 2023 and is funded by European and state funds, aims to develop combined aquaculture in the Baltic Sea. The aim is to promote the spread and economic viability of combined fish and shellfish farming in the Baltic Sea and to gain greater recognition for it. Furthermore, environmental compatibility and economic efficiency are to be evaluated in order to create aquaculture production in the western Baltic Sea off Mecklenburg Western Pomerania that is as sustainable, environmentally friendly, local, and accessible to all as possible. The overall project represents a new approach, as the difficult hydrodynamic and harsh conditions, characterized by high wind speeds and accompanying wave heights, vary greatly in the coastal region of the Baltic Sea, for example, from those in the fjords of Norway. For fish aquaculture, the target fish species is rainbow trout (Oncorhynchus mykiss). The target shellfish species that is produced for shellfish aquaculture is the blue mussel (Mytilus edulis). Other objectives of the project in the field of fish farming include two separate pen systems that are to be installed and tested in the western Baltic Sea and subsequently stocked with fish. One system, called "The Cage," is a net-supported system; the other, called "Björn," is a steel cage shaped like a truncated octahedron. Three different systems were designed and visualized for mussel farming. These include one underwater longline system and two surface longline systems, one of which is a double longline system and the other a single longline system with different types of buoys. In early 2024, all three shellfish systems, as well as the net support system "The Cage," were designed, visualized, and then hand-built on land. In the end of 2024, all of the constructed systems were transported to the Nienhagen Fisheries Reserve, located in the western Baltic Sea not far from Rostock, and installed there for a tasting phase. In early 2025, two of the three installed mussel farms were lost due to severe winter storms; only the above-water double-line system could be saved. However, the first mussel harvest was lost due to the storms and predators. Because of the difficult conditions throughout 2025, only a single mussel farm was installed during the entire year and was harvested at the end of 2025. In mid-2025, the first fish were stocked into the net carrier system over a three-month period. However, due to predators, half of the stock was lost, so that by mid-2025 only half of the stock could be harvested. After the harvest, the net carriers were restocked with rainbow trout following a net change and harvested at the end of 2025. Both harvests yielded excellent results in terms of both fish biomass and mussel biomass. The total catch weighed approximately 209.1 kg, consisting of 417 trout, resulting in an average weight of 0.5 kg per fish. 7.2 kg of commercially viable mussels were harvested per meter of collector line. Extrapolated to the entire 450-meter double-longline system, this would amount to approximately 3,237 kg of commercially viable mussels. Other results such as fish index and mussel index, were also wide above average In early 2026, all three mussel systems were reinstalled and equipped with data loggers that record axial movement. Thus, the mussel system with the least axial movement will be the most efficient in terms of losses and, consequently, the most useful and resilient under harsh conditions. For a future project we want to establish a community to pool their knowledge and expertise in order to produce a sustainable blue circular nutrient economy in the Baltic Sea area. Substituting fishmeal with regional mussel protein production to reduces pressure on wild stocks and closes the nutrient cycle, making regional offshore aquaculture circular.