Branchial circulation and gill morphometrics in the sturgeon Acipenser transmontanus, an ancient Chondrosteian fish

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Abstract
Gill morphometries and branchical circulation have been examined in sturgeon, Acipenser transmontanus, weighing from 1 to 336 kg.Weight-specific gill area of the lamellar blood channels, approximately 0.9 cm2/kg in 2–8 kg Acipenser, is low compared with that of other fishes, and probably reflects a low activity level and metabolic rate in the sturgeon. Gill arches III–VI contribute 98% of the respiratory surface area of the sturgeon. However, Acipenser retains gill tissue representing all six embryonic arches. The spiracular pseudobranch (arch I) is perfused with oxygenated blood, while the well developed opercular gill (arch II) receives deoxygenated blood from the ventral aorta. Although comprising only 2% of total gill surface area, anatomical evidence indicates that gill arch II functions in gas exchange and is the major source of blood for certain ventilatory muscles of the operculum.Lamellae on all branchial filaments of all arches can be placed into one of five surface area classes, each class bearing a quantitative area relationship to all others. Since surface areas of the various gill arches also bear certain quantitative and consistent interrelationships, total gill surface area could be accurately predicted for sturgeon on the basis of data from single hemibranchs.