Abstract: Abstract：Fish feeding is a key link to the pre-processing of fishes, as the recent increase in the reproductive outputoffreshwater fishes.At present,mechanical processingis widely used in the pre-processingof freshwater fishes. However, mostfish pre-treatment equipment is lacking of the specific device to automatically position the fish body when fish feeding, ratherthan manually feeding. The current manual feeding is restricting the industrial development of the pre-treatment processing forfreshwater fishes due to its high labor intensity and low efficiency when fish feeding. To realize the automatic feeding offreshwater, this present study aimed to design a sort of mechanical orientation device for pre-treatment processing equipmentwhen fish feeding. A typical bulk freshwater fish, Carassius auratus,was selected as research objects. This selection is becauseCarassiusaur atushas approximately wedge-shape abdomen in the cross-sectional fish body, where exhibit certain mechanicalcharacteristics when the fish's abdomen and back were squeezed at the same time. Asuitable method was then proposed for theorientation of the freshwaterfish'sabdomen and back, as well the related mechanism was analyzed.A test device was finallydesigned and manufactured for the orientationof the freshwater fish'sabdomen and back. The systematic experiments werecarried out on the test device for the freshwater fish'sabdomen and back when fish feeding. The orientation success rate andorientation time were recoded during the test,to be used as the evaluation index of each test. The main parameters of the testdevice were optimized, and the optimal values were also determined to locatethe freshwater fish'sabdomen and back. Themain working parameters of the test device were set as the roller shape, roller gap, fish bodytransport speed and the rollerrotation rate. First, singlefactor tests were utilized to investigate the effects of these parameters on the abdomen and backorientation of the fish body. Then, an orthogonal test was performed to systematically explore the specific factors on theposition operation of the fish body. The results of the orthogonal test showed that the combination among various factors in theoptimal level was: the gap of the roller was 50mm, the rotation rate of the roller was 50 r/min, and the transport speed of thefishbody was 0.6 m/s.Under this optimal level combination, the orientation success rate was 100%, orientation time was 0.55second, indicating that the working state of the test device for freshwater fishes'abdomen and back was reached the optimalstate. The related results on the abdomen and back orientation of freshwater fishes can provide insightful theoretical basis andsound technical reference for the development of orientation equipment for feeding in freshwater fish processing.