Selective control of branchial arch perfusion in an air-breathing Amazonian fish Hoplerythrinus unitaeniatus

Vascular responses to adrenergic and cholinergic agonists were investigated in the air-breathing teleost Hoplerythrinus unitaeniatus during in situ saline perfusion of the ventral aorta.The vasculature resembled that of other teleosts in having inhibitory β-adrenergic receptors and excitatory muscarinic receptors, probably located in the gills. The gas bladder vessels were apparently devoid of adrenergic and cholinergic receptors.The dorsal aorta was specialized between gill arches 2 and 3 in such a way that the dorsal aorta probably received most of its blood supply from arches 1 and 2. Arches 3 and 4 supplied the large coeliac artery whose major branch was to the gas bladder. Acetylcholine reduced the number of perfused gill arches so that most of the ventral aortic flow was directed towards the gas bladder through arches 3 and 4. This was seen as a possible solution to the problem of transbranchial oxygen loss that could arise if blood oxygenated at the gas bladder was exposed to hypoxic water at the gills.