Gill ventilation in the sturgeon, Acipenser transmontanus: unusual adaptations for bottom dwelling.

Measurements of branchial cavity water pressures and flow patterns, arterial blood PO2 and pH, and oxygen utilization and uptake have been made in undisturbed, free swimming sturgeon, Acipenser transmontanus. Although the jaws are degenerate and the oral apparatus is highly modified for feeding, gill ventilation is nonetheless powered by a buccal force pump and an opercular suction pump common to most bony fishes. The reduced spiracles play little or no role in gill ventilation. In sturgeon in which water intake through the ventrally located mouth was experimentally eliminated, a condition which may often develop when these fish forage in mud and sand on river substrates, effective ventilation of the gills was maintained with water drawn into the branchial cavities in a retrograde fashion solely through permanent openings in the upper regions of the opercular slits. O2 uptake and transport also remained at control levels. It is suggested that this unusual alternative mode of gill ventilation in the sturgeon represents an important respiratory adaptation to bottom dwelling and feeding.