. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 100 JOHN L. ROBERTS cm 4 water pressure 0. 20 40 60 Flow cm sec"1 80 100 120 FIGURE 6. Secondary calibration of a Blazka swimming tunnel (respirometer type) with a combined impact-reverse pitot tube in the axial Mow of the swimming chamber to give pressure equivalents of flow velocity in centimeters of water. The primary calibration was obtained by use of a ducted, impeller flow-meter (Marine Advisers Inc., La Jolla, California; model B-7C). Minimal and maximal estimates for across-gill differential pressures have been
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 100 JOHN L. ROBERTS cm 4 water pressure 0. 20 40 60 Flow cm sec"1 80 100 120 FIGURE 6. Secondary calibration of a Blazka swimming tunnel (respirometer type) with a combined impact-reverse pitot tube in the axial Mow of the swimming chamber to give pressure equivalents of flow velocity in centimeters of water. The primary calibration was obtained by use of a ducted, impeller flow-meter (Marine Advisers Inc., La Jolla, California; model B-7C). Minimal and maximal estimates for across-gill differential pressures have been extrapolated on the ordinate according to the range of swimming speeds permitting ram gill ventilation for the fishes listed in Table II. impact-reverse pitot tube with variable tip- and downstream orifices. The com- parison has limits. The pitot tube typically is a zero-flow pressure measuring device so the resistance between orifices is infinite. The branchial system differs in that through-flow occurs as a volume rate determined primarily by the resistivity of the gill screen. Figure 6 illustrates the pressure differential developed between impact and reverse openings of a pitot tube located in a "swimming" respirometer of the Blazka type (loaned by Dr. F. E. J. Fry, University of Toronto) relative to water flow velocities from 0 to 120 cm-sec'1. The extrapolated buccal-post branchial pressure range also is shown (ordinate). This range of pressure dif- ferences corresponds to minimal and maximal swimming speeds for ram gill ven- tilation by the fish species listed in Table II (, blue runner and bluefish, re- spectively). Assuming that a resemblance to the combined impact-reverse pitot is reasonable, then an across-gill pressure drop as low as cm enables some fish to swim as slowly as 35 cm-sec'1 and still support ram gill ventilation. Muir and Buckley (1967) have determined via buccal and opercular cannulas that the average pressure necessary to force water
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
