The ventilatory and cardiovascular responses of conscious, decerebrate, and anesthetized spontaneously breathing (ASB) catfish (Ictalurus punctatus) were measured at three different water O2 tensions [Formula: see text] to determine the advantages and limitations associated with each experimental preparation. Ventilation of the decerebrate and ASB catfish was assisted to maintain arterial [Formula: see text] levels and acid–base balance at values similar to those of conscious fish. All groups exhibited decreased heart rate (fh) and increased dorsal aortic blood pressure (PDA), and increased either ventilatory rate (fg), opercular pressure (POP), or both during hypoxia. Conscious catfish were extremely sensitive to outside disturbances and responded with transient bradycardia and apnea. The fg of decerebrate fish was consistently high and was little affected by changes in [Formula: see text]. Altered ventilation after decerebration may be due to interference with suprapontine structures involved in the control of ventilation. Unlike conscious fish, both decerebrate and anesthetized fish had maximal heart rates in normoxia and responded to hyperoxia by reducing fh. Anesthesia produced a relative tachycardia and attenuated the hypoxic bradycardia of ASB catfish, but had little effect on ventilatory reflex responses to hypoxia.