Shellfish (bivalvia) are suitable indicator organisms for biomonitoring and assessment of environmental quality because they feed and breathe using gills, filter large amounts of seawater, phytoplankton and particulate organic matter, and thus accumulate present pollutants, and at the same time purify the environment. According to environmental conditions and pollution present, bivalves react to stressful conditions by changing their behavior, closing and opening their shells, changing the intensity of filtering. As a result of exposure to pollutants, other biological effects occur, from damage and changes at the level of molecules, organelles, cells, tissues, organs, organic systems, to the whole organism. Through communication and cooperation with scientists from the Center for Marine Research in Rovinj of the Ruđer Bošković Institute, the need for the development of a built-in computer system that would measure selected environmental parameters and monitor the filtering function by measuring shell openness emerged. Valve Gaping (VG) during experimental exposures of shellfish, primarily the mussel Mytilus galloprovincialis. VG-MM English was developed for this purpose. Valve Gaping - Mussel Monitor system based on Arduino microcontroller primarily intended for laboratory experimental work with mussels. The VG-MM system allows, depending on the need, to connect 6 or 12 Hall sensors and monitor the VG function of the same number of shellfish connected to the device or 6 sensors connected via a 20 m long UTP cable for measuring the VG of mussels in outdoor pools, i.e. via a WIFI network. The Arduino microcontroller platform was chosen as the basis for the creation of an embedded computer system due to its multiple functionality: low power consumption, high modularity and availability of components. To measure the VG filtering function, i.e. the openness of bivalve shells, analog Hall magnetic flux sensors were chosen, taking care to make the system robust, practical and functional, with the possibility of further upgrading, improvement and potential wide application of the created prototype of the built-in VG-MM computer system. The developed VG-MM system was successfully applied to monitor the VG function, i.e. the normal filtering of mussels during several days of laboratory keeping in pools (0-24 hours) and real time observations of attacks and predation of mussels after exposure to the invasive predatory mantled Imogine mediterranea as an example of a relative threat in farms shellfish in the area of ​​the Istrian County.