Antarctic fishes have a limited capacity for catecholamine synthesis.

To determine whether an attenuated stress response is a general feature of Antarctic fish or is dependent on ecotype, the capacity for catecholamine synthesis within the head kidney and plasma levels of the primary stress hormones (catecholamines and cortisol) were determined in species with a range of activity patterns. Tyrosine hydroxylase (TH) activities were similar in both sluggish (Gobionotothen gibberifons, 153+/-22 nmol g(-)(1 )h(-)(1), mean +/- s.e.m.) and active (Notothenia rossii, 185+/-39 nmol g(-)(1 )h(-)(1), Dissostichus mawsoni, 128+/-31 nmol g(-)(1 )h(-)(1)) pelagic nototheniids, but only 30 % of those in Atlantic cod (Gadus morhua, 393+/-88 nmol g(-)(1 )h(-)(1)) at the same temperature. TH activities were even lower in white-blooded channichthyids (Chaenocephalus aceratus, 74+/-16 nmol g(-)(1 )h(-)(1) and Champsocephalus gunnari, 53+/-17 nmol g(-)(1 )h(-)(1)), although values in Chionodraco rastrospinosus were similar to red-blooded species (178+/-45 nmol g(-)(1 )h(-)(1)). Circulating catecholamine levels were extremely high in all species after fishing stress, with adrenaline levels 3-4 times higher than noradrenaline levels. Cortisol levels remained low, ranging from 1.33+/-0.58 ng ml(-)(1) in Champsocephalus gunnari to 44.9+/-25.0 ng ml(-)(1 )in Dissostichus mawsoni. These data suggest that depressed catecholamine synthesis is typical of Antarctic fish regardless of life style, although they are able to release extensive stores from the chromaffin tissue under conditions of extreme trauma. Cortisol does not appear to be an important primary stress hormone in these species.