Changes in level of ATP and its related compounds were investigated in the muscle of eight species of freshwater fishes and compared with those of seawater fishes during ice storage. Changes in content of ATP and its related compounds showed the same pattern through the storage periods among all species of both freshwater and seawater fishes tested; IMP accumulated in the early stage of storage with the rapid decrease of ATP, and then inosine (HxR) and hypoxanthine (Hx) increased during storage with the decrease in IMP level. IMP-degrading and HxR- and Hx-forming rates were different among the fish species, and thus the K value-increasing rate showed considerable difference in the range of 1.6-14.6%/day in freshwater fishes and 1.2-24.6%/day in seawater fishes, respectively. These findings suggest that the K values of all freshwater fishes do not increase more rapidly than those of seawater fishes during ice storage.