We examined potential vasomotor control mechanisms in an Antarctic fish ( Trematomus bernacchii; usual core temperature approximately −1°C), comparing sensitivity to agonists by means of the cumulative dose response and potency with reference to depolarization by 50 mM KCl. In efferent branchial arteries, norepinephrine (NE) produced ∼20% of the maximal KCl tension and ∼40% in the presence of 10−3M sotalol, suggesting a modest contribution of α- and β-adrenergic tonus [half-maximal response (pEC50) = 6.29 ± 0.37 M]. Carbachol (CBC) and serotonin (5-HT) had different sensitivities (pEC50= 4.50 ± 0.40 and 6.82 ± 0.08 M, respectively) but similar potencies (21.6 ± 11.1 and 31.1 ± 5.3% of KCl). A related species from warmer waters around New Zealand, Paranotothenia angustata, had similar vascular reactivity for NE (pEC50= 5.48 ± 0.31 M), CBC (pEC50= 4.94 ± 0.22 M), and methysergide-sensitive vasoconstriction with 5-HT (pEC50= 6.22 ± 0.40 M). Agonist potencies were 9, 65, and 45% that of KCl, respectively. Bovichtus variegatus, a member of the phylogenetic sister group to the notothenioids, also gave broadly similar responses. In contrast, Dissostichus mawsoni, a pelagic Antarctic notothenioid, showed a dominance of vasodilatation over vasoconstriction, with sensitive isoprenaline (pEC50= 6.66 ± 0.05 M) but weak serotonergic (5.2 ± 1.5% KCl) responses. The unusual dominance of serotonergic control appears to be primarily a consequence of evolutionary lineage rather than low environmental temperature, but the pattern may be modified according to functional demand.