The shuttlebox performance of goldfish was studied under standardized conditions in a variety of problems—with or without an avoidance contingency, a conditioned stimulus (CS)-termination contingency, and an escape contingency. The effects of CS-only, unconditioned stimulus (US)-only, and explicitly unpaired training were also examined. All the data could be simulated quantitatively with a version of OH Mowrer's (1947) 2-process theory expressed in 2 learning equations (1 classical, the other instrumental) and a performance equation. The good fit suggests that the theory is worth developing further with new experiments designed to challenge it.