Abstract: Inland saline-alkaline waters provide potential space for expanding aquaculture, but elevated salinity and carbonate alkalinity can impose strong osmotic and acid-base stress on freshwater fish. This study compared the acute tolerance of one-year-old Ctenopharyngodon idella (114.56 ± 2.29) g, Hypophthalmichthys nobilis (117.45 ± 2.66) g, and Hypophthalmichthys molitrix (159.45 ± 1.87) g to salinity and alkalinity, and evaluated whether short-term fixed-concentration acclimation affected survival during a subsequent challenge. Separate 96-h acute tolerance tests were conducted using NaCl for salinity and NaHCO₃ for alkalinity. The 24, 48, and 96 h median lethal concentrations (LC₅₀) were estimated from measured exposure concentrations and mortality, and safe concentrations (SC) were calculated using an empirical acute-toxicity equation. In a separate acclimation–challenge experiment, fish were acclimated for 96 h to approximately one-quarter, one-third, or one-half of the species-specific 96-h LC₅₀ and were then challenged for 48 h at a concentration close to the corresponding 96-h LC₅₀. The estimated safe salinity concentrations for C. idella, H. nobilis, and H. molitrix were 3.20, 3.67, and 4.00 g/L, respectively, indicating a salinity-tolerance ranking of H. molitrix > H. nobilis > C. idella. The estimated safe alkalinity concentrations were 22.27, 17.69, and 11.72 mmol/L, respectively, with an alkalinity-tolerance ranking of C. idella > H. nobilis > H. molitrix. During the salinity challenge, survival of C. idella acclimated at 2.98 and 3.96 g/L did not differ significantly from that of the unacclimated group, whereas survival at 6.01 g/L was significantly lower. In H. nobilis, survival in the 3.13 g/L acclimation group was significantly higher than that in the unacclimated group, whereas survival in the 4.09 and 6.19 g/L groups was significantly lower. In H. molitrix, survival in all acclimation groups was significantly higher than that in the unacclimated group, although survival decreased at the highest acclimation concentration. During the alkalinity challenge, survival of C. idella in the 17.30 and 23.21 mmol/L acclimation groups was significantly higher than that in the unacclimated group, whereas survival in the 34.55 mmol/L group was significantly lower. In H. nobilis, survival in the 14.45 mmol/L acclimation group was significantly higher than that in the unacclimated group, whereas no significant differences were observed at 19.25 and 28.90 mmol/L. In H. molitrix, survival in all three acclimation groups was significantly higher than that in the unacclimated group, but generally decreased with increasing acclimation concentration. These results show that the three species differ in their acute tolerance to salinity and alkalinity and that the effects of short-term acclimation on subsequent challenge survival are species- and concentration-dependent. The results provide baseline data for acute tolerance assessment and short-term acclimation design, while their applicability to long-term culture and the underlying physiological mechanisms require further validation.