The catecholamine hormones epinephrine (adrenalin) and norepinephrine (noradrenalin) are associated with more immediate reactions to stress, and are released when situations requiring a fight or flight response occur. The release of catecholamine hormones into the bloodstream causes increases in cardiac output, blood sugar, respiration, oxygen uptake, and blood flow to the gills. This prepares fish to better cope with threats to territory and safety. These responses are usually short in duration and are considered acute stresses.