Optimizing the Processing of Shellfish (_Mytiilus edulis_ and _M. trosulus_ Hybrid) Biomass Cultivated in the Low Salinity Region of the Baltic Sea for the Extraction of Meat and Proteins  
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the most promising measures to remove these excess nutrients from the Baltic Sea [3]. The most promising aquaculture species in the Baltic Sea is the blue mussel, a hybrid of the two species _Mytiilus edulis_ and _Mytiilus twosulus_[6]. Earlier studies demonstrated that shellfish farming in the Baltic Sea is efficient, cost effective, and removes large amounts of nutrients [3; 7]. Comprehensive environmental monitoring of all existing mussel farms in the Baltic Sea did not identify any significant negative environmental impacts in any aspect over a three-year period [7]. In addition to the above, Baltic Sea shellfish have very low levels of different toxins (e.g., heavy metals, PCBs, benzopyrenes, algal toxins), which means that this resource can be effectively used for human consumption and/or animal feed [8]. Despite these positive aspects, there are still many challenges that hinder the development of the mussel farming industry in the Baltic Sea region [9]. When prepared for human consumption, mussel meat yields should be >30% to have a market as a food product. Thus, mussels with lower meat yields are normally rejected due to their low commercial value and are classified as by-products. Salinity is low (below 10) in the large parts of the Baltic Sea, and therefore blue mussels are much smaller in the Baltic Sea than in the North Sea. Looking at the average size of a mussel in the Baltic Sea (2-3 cm), more than 95% of the catch is theoretically classified as by-products. For shellfish aquaculture to be successful, it is necessary to address product valorization to make this aquaculture sustainable [3]. The development of innovative products and production lines is essential for the cultivation and marketing of new species, as at present there is no effective use of shellfish collected from farms in the low-salinity parts of the Baltic Sea. The small size of mussels farmed requires viable solutions of processing mussels for feed, food, or some high-end product. To date, however, the biomass of mussels has been very poorly exploited in the Baltic Sea region. As blue mussels in marine waters are reasonably large enough to be directly used, and fresh mussels are in high demand, there are not many studies on valorizing mussels further for human consumption. Amongst commonly used methods of extracting meat and protein fractions, acid and alkaline solubilization techniques have been used [10]. In addition, proteins can be efficiently extracted using enzymatic hydrolysis [11]. The necessity for valorization mostly comes from by-products and the biomass that is discarded from direct consumption [12]. Among very few publications on mussel valorization for human consumption, the mussel by-products can be used to produce mussel pate [13] using the well-established technological methods of tuna pate [14]. Besides human consumption, mussels can be used for many other applications. The inhibitor found in the liquid extracted from the mussel successfully inhibits enzymatic browning, making it a valuable \"preservative\" in the fruit and vegetable industry, as natural inhibitors are better absorbed by humans [15]. Mussel shells can be heat treated to effectively produce CaO powder [16] to be used in building materials, food additives, pharmaceuticals, animal feed, and plastics [17]. Further refining technology of this material results in high-purity nano-sized calcium carbonate powder that can be used for niche applications such as scaffold fabrication, bone regeneration, and as a catalyst for high-temperature reactions [18]. Moreover, mussel meal can be used for bird feed. Here, mussels are seen as a good and high-quality protein source for poultry, and may replace fish meal in organic diets for laying hens and broiler chickens [19].