The effects of thermoregulatory behaviours on gut blood flow in white sturgeon Acipenser transmontanus before and after feeding was studied using a blood flow biotelemetry system in combination with a temperature preference chamber. This is the first study to look at cardiovascular responses to feeding in white sturgeon, and also the first time behavioural tests in fish have been combined with recordings of cardiac output, heart rate, cardiac stroke volume and gut blood flow. The results showed strong correlations between gut blood flow and temperature choice after feeding (R(2)=0.88+/-0.03, 6-8 h postprandially and R(2)=0.89+/-0.04, 8-10 h postprandially) but not prior to feeding (R(2)=0.11+/-0.05). Feeding did not affect the actual temperature preference (18.4+/-0.7 degrees C before feeding, 18.1+/-0.7 degrees C, 6-8 h postprandially and 17.5+/-0.5 degrees C, 8-10 h postprandially). Fish instrumented with a blood flow biotelemetry device, and allowed to move freely in the water, had a significantly lower resting heart rate (37.3+/-0.26 beats min(-1)) compared with the control group that was traditionally instrumented with transit-time blood flow probes and kept in a confined area in accordance with the standard procedure (43.2+/-2.1 beats min(-1)). This study shows, for the first time in fish, the correlation between body temperature and gut blood flow during behavioural thermoregulation.