Effect of temperature and thermal stress on the hemodynamics of the scallop Chlamys farreri, as indicated by Doppler ultrasonography

The effect of temperature and thermal stress on cardiac activity and hemodynamics of a temperate scallop species Chlamys farreri was revealed using Doppler echocardiography. The variation scope of eight hemodynamic parameters within the optimal temperature range (8-26 °C) was determined, including heart beat rate (HR), acceleration of blood flow (ABF), peak systolic velocity (PS), end diastolic velocity (ED), maximum & minimum instantaneous blood flow (Max & Min-IBF), resistive index (RI) and PS/ED.The effects of two thermal stress factors were examined, prolonging high water temperature (28-30 °C) and fast heating (2 °C h−1), on hemodynamics of gill blood vessels. The HR-based Arrhenius break temperatures (ABTs) of the scallop under two stress factors were 29.32 °C and 32.37 °C respectively. Results showed that the scallop has a short-term tolerance to acute thermal stress compared with prolonging high temperature. When temperature rose above 28 °C, the PS/ED ratio and RI exceeded the thresholds of 3.0 and 0.63, respectively, indicating potential damage and malfunction of the blood vessels. Low water temperature (6 °C) may also have negative impacts on blood circulation. When faced with a rapidly rising temperature, the scallop cannot adjust its heartbeat in time, but in compensation, the scallop still supplied sufficient hemolymphs to the gill by expanding the diameter of the arteries. The cause of the scallop's death may be different under two thermal stresses: prolonging high temperature caused cardiac failure and physical damage of the artery, whereas rapid heating caused serious tachycardia accompanied by cardiac failure.