although in these cases the fish were exposed to the anaesthetics for
longer than in the present study. It is known that during periods of
stress, the release of catecholamines can cause the release of erythrocytes
into circulation fromthe spleen (Kita and Itazawa, 1989), thus increasing
the haematocrit and haemoglobin levels. The absence of any
variation in these parameters indicates that exposure to the anaesthetics
is not an important stimulus for activation of the sympathetic
nervous system, the endpoint of which is the release of catecholamines
into blood from the chromaffin tissue. In accordance with this conclusion,
sedation or anaesthesia in salmonids did not stimulate release of
catecholamines from the chromaffin tissue (Gerwick et al., 1999;
Rothwell et al., 2005).