Electrocardiogram of a marine fish,Pagrus major,exposed to red tide plankton,Chattonella marina

Examinations of the electrocardiogram of Pagrus major exposed to Chattonella marina, a planktonic organism causing red tide, were made to determine the physiological effects on fish. The heart rate decreased as a result of the extention in the interval between T and P waves. The decrease in heart rate with the extended intervals between T and P waves was also recognized in the condition of decreased dissolved oxygen. Also, the decrease in heart rate of the fish exposed to the red tide occurred while the fish was struggling. This reduction seems to be caused by the strong tension of the vagal nerve. Upon exposure to C. marina at high cell concentration, the heart beat at a very low frequency after 30 min. The very low heart rate is expected to limit seriously the oxygen uptake by the gill, because the cardiac output is probably very low in this situation.