Investigation of the cardiovascular control of notothenioid fish (Pagothenia borchgrevinki and Trematomus bernacchii)

It has been shown that under stress, red blooded notothenioids increase their haematocrit by contracting the spleen thus releasing red blood cells and increasing the heart rate. The increase in heart rate appears to be the result of a decrease in cholinergic inhibition rather than adrenergic (adrenaline mediated) stimulation. The aim was to determine, in vivo, if levels of circulating adrenaline change during stress. The control of blood flow through the heart and gills of Antarctic fish was experimentally investigated on individuals of Pagothenia borchgrevinki and Trematomus bernacchii. Fish were dissected to gain an understanding of the blood system and to determine where to gain access to the dorsal and ventral aorta. Resin casts of the blood system were made. The location of cholinergic, adrenergic and peptidergic receptors in the heart, gills and blood vessels was investigated from sections and isolated blood vessels using immunohistochemical techniques. Fish were stressed by forcing them to swim and physiological parameters (heart rate and ventral aortic blood pressure) were measured via the indwelling cannulae. Blood samples were taken to measure haematocrit, blood haemoglobin, plasma osmolarity and plasma adrenaline. Samples were also analyzed for catecholamines. The effects of two stressors (hypoxia and swimming) on blood flow and heart rate and the factors controlling these changes was investigated. A range of drugs was injected into the fish and their effects were monitored (dorsal and ventral blood pressure, blood pressures, heart rate, cardiac output, stroke volume and resistance to blood flow at the gills and at the systemic capillaries).