Abstract: The effect of hydrogen ion concentrahon (pH) on fish, under certain circumstances, is closely connected with the amount of oxygen dissolved in waten. The auther has designed a controlling apparatus which can be regulated under conditions of dissolved oxygen and other physical and chemical factors most favorable for fish, to investigate the survival adaptability to pH of fish by altering the pH of the water. 412 fingelings being tested for 60-144 hours show that the survival adaptability of Mylopharyngodon piceus, Ctenopharyngodon idellus, Hypophthalmichthys molltrix and Aristechtys nobilis is within the pH range 4.6-10.2, and that of cyprinus carpio is within the pH range 4.4-10.4. It is also found that the individuals of each species have a certain transitional scope between the limits of the surviving and the totally lethal pH range, during which the fish is most sensitive to even slight changes in pH.