This work describes the research aimed at determining the value of the basic parameters of fish cutting on treatment with a high-pressure water jet. Assuming a constant feed speed, distance of the nozzle from the processed raw material, and spray angle of the water jet for six diameters of the water nozzles, the supply pressure value was determined. Supply pressure at which the water stream has enough energy to fully cut the muscle flap is also determined. The tests were carried out on samples obtained from rainbow trout, considering the size of the carcasses and the place of cutting. Analysis of the obtained results showed that both the size of the carcass and the cutting site affect the value of the supply pressure. However, regardless of this, the full cut of the lobe without the skin can be obtained by feeding the jet with a pressure of 3.5 MPa. This amount of pressure can easily be achieved using a Karcher pressure washer. To effectively apply this technology to the fish processing industry, it is necessary to extend the tests with further processing parameters such as the feed speed of the nozzle.