Physiology of Finfish and Shellfish

2.2.18. Aneural Cardiac Vascular Control

This is affected by changes in blood volume, by direct responses of heart muscle to temperature changes and by secretions of various organs. Along with swimming movements in certain species, changes in blood volume will also affect venous return. A rise in temperature causes increase in the rate of heart beat in some species. Thus, blood flow increases and the body receives more oxygen, which is necessary to maintain higher metabolic rate of the body in warm water. Certain hormones like catecholamines such as epinephrine also affect aneural control by increasing heart rate.

Decrease in heart rate is also affected by some external stimuli, as the sudden flash of light, touch, mechanical vibration or movement of enemy or prey.