The spleen of notothenioids releases red blood cells during times of stress to increase oxygen uptake. The more red blood cells in the blood, the more viscous it is and the harder it is to pump around the body in such cold conditions. Notothenioids therefore have a reduced red blood cell volume in their blood during times of rest. The control of red blood cell release from the spleen was ... investigated. A spleen was isolated in situ. The splenic nerve was stimulated electrically to investigate the contractile properties. Drugs were injected into the perfusion medium to determine if the splenic nerve is composed entirely of cholinergic nerves, the first time cholinergic control of the spleen has been demonstrated in a vertebrate. Isolated samples of spleen were used experimentally to create dose response curves for acetylcholine and adrenaline and blood vessel contractibility was determined.