THE IRRIGATION OF THE GILLS IN FISHES: I. STUDIES OF THE MECHANISM OF BRANCHIAL IRRIGATION

Abstract

A technique which does not interfere with normal respiratory movements was developed for measuring the changes in hydrostatic pressure in the oral and opercular cavities of fish breathing at various intensities. This consisted of inserting polyethylene tubing of small diameter through the cleithrum into the opercular cavity and through the rostrum into the oral cavity. These cannulae were connected with manometers which were used together with optical lever systems to record the time course of changes in hydrostatic pressures in the two components of the branchial pump.In the white sucker, brown bullhead, and carp the flow of water over the gills is nearly continuous. There are only brief periods when the pressure in the opercular cavities exceeds that in the oral cavity and therefore only brief reversals in flow in which some water may be returned over the gills. The slits between adjacent hemibranchiae of neighboring gills were observed to open rhythmically during moderate and heavy breathing. This observation is contrary to the thesis of many workers that water bathing the gills flows only through the minute pores between adjacent lamellae. Such opening of the gill slits may have a significant effect in the operation of the gills.