From Rufus Wells, University of Auckland New Zealand
The conclusion that fish do not show emotions, based on increased heart rate
during stress, is flawed
(In Brief, 9 May, p 24).
Rather than regulating their
cardiac output by varying heart rate like mammals, lower vertebrates change the
stroke volume of their hearts. The heart of most fish is a simple volume pump
coupled with a single circulation, so too much excitement might rupture the
gills if there were a link between the heart and stress.
Moreover, it is well known that the primary endocrine responses to stress in
fish are a surge of catecholamines, followed by a sustained release of
cortisol—precisely the same mechanism as in humans.
The circulating concentrations of adrenaline and cortisol that occur in fish
exposed to such mild stresses as a person walking into the viewing gallery of an
aquarium suggest that fishes are sensitive souls indeed.
Auckland
