The behavioral responses of goldfish to a variety of amplitude‐modulated (AM) acoustic signals were studied using a stimulus generalization paradigm in combination with a classical conditioning method. Measurements were thus allowed of the equivalence among various complex and simple signals in controlling the conditioned respiration response. The goldfish's conditioned response to AM signals were found to be controlled by carrier frequency, modulation depth, and to a lesser extent, by modulation frequency in the 40‐Hz range. On the other hand, pure‐tone frequency exerted minimal behavioral control for subjects conditioned to AM signals. Subjects conditioned to a 40‐Hz pure tone tended to generalize maximally to an AM signal having a 40‐Hz modulation rate. The results indicate the degree to which the goldfish can use much of the information present in complex periodic acoustic signals and suggest the existence of periodicity pitch in fish.