[Objective]To investigate the effects of acute freshwater stress on the tissue structure of gill, heart, spleen and liver of juvenile Eleutheronema tetradactylum, in order to provide reference for exploring low salinity culture and breeding of improved varieties. [Method]Juvenile E. tetradactylum, temporarily reared at salinity 9, were placed directly into an aquarium with a salinity of 0. Live samples were taken at 2, 6, 12, 24, 48 and 72 h. Histological methods were used to study the gill, heart, spleen and liver structures of juvenile E. tetradactylum under different durations of acute fresh-water stress. [Result] In juvenile E. tetradactylum, the length of the gill lamellae tended to increase gradually, the width of the gill lamellae decreased and then increased, the spacing of the gill lamellae increased and then decreased, and the number of mitochondria-rich cells continued to increase when exposed to acute freshwater stress. The size of the myocardial transverse muscle, the size of the cardiomyocyte gap and the size of the interstitial blood vessels all showed a trend of increasing and then decreasing. The peak of myocardial transverse muscle size was at 12 h of stress, and the peak of myocardial interstitial and interstitial blood vessel size was at 24 h of stress. The white marrow area and marginal zone area gradually increased from 0 to 24 h of stress, and the colour of melanin macrophages also gradually deepened, reaching a peak at 24 h of stress and then gradually decreasing. 72 h later, the red pulp, marginal zone, white pulp and melano-macrophages were roughly restored to the level of the control group. In the control group, the hepatocytes were large, polyhedral, with rounded nuclei and centrally located, and some hepatocytes had 2-3 nuclei; the hepatic plate was clearly defined; the hepatic blood sinusoids were normally distributed among the hepatocytes. During 24 h of stress, the hepatic plate structure was gradually blurred and the gap between the hepatic sinusoids was gradually widened, reaching a peak at 24 h of stress; during 24-72 h of stress, the hepatic plate structure gradually regained clarity, the gap between the hepatic blood sinusoids was gradually reduced and some nuclei lost their intrinsic morphology. [Conclusion] Under freshwater stress, the tissues (gills, heart, spleen) of juvenile E. tetradactylum exhibit stress responses within 24 h, and adapt to a low salt environment after 24 h. However, some liver cells are still difficult to recover from acute freshwater stress. This indicates that juvenile E. tetradactylum have some ability to adapt to low salt stress. [ABSTRACT FROM AUTHOR]