The secondary lamellae of larval and adult lamprey gills alternate on either side of filaments, become more widely spaced as filament length increases and increase in area as the body weight becomes greater. In terms of body weight, however, the number and total length of the filaments and the total number of secondary lamellae, together with the number of secondary lamellae found on a given distance of filament, increase during metamorphosis. The reverse is true, however, of the bilateral area of the secondary lamellae which is considerably greater in ammocoetes. The total gill area, expressed in terms of body weight, of both larval (1462- 2717 mm2 g -1) adult (1402-2337 mm2 g-1) fluviatilis are comparable with those found in the most active teleosts. The harmonic mean of the water-blood pathway in the secondary lamellae ranged from 4.39 mum in a 0.25 g ammocoete to 1.42 mum in a 3.5 g adult L. planeri. Scanning electron microscopy showed that the surface of the secondary lamellae were covered with a thick layer of mucus after fixation in 5.0% glutaraldehyde, whereas at high (25.0%), and particularly very low concentrations (0.1%), it was often virtually absent. Prominent raised edges separated adjacent cells, and the cell surface bore a mass of short convoluted low microridges. If 5.0% glutaraldehyde stimulates the discharge of the raucous cells, the microridges under normal conditions would increase the surface area by 1.8 times and produce a localised area of microturbulence that would facilitate gaseous exchange. Measurement of standard oxygen consumption during the six stages of metamorphosis showed a rise from 20.3 to 50.5 mul g-1 h-1 in L. planeri and from 29.3 to 60.4 mul g-1 h-1 in L. fluviatilis. In L. planeri the mean rate rose to 73.3 mul g -1 h-1 in males and declined to 44.1 mul g -1 h-1 in females. Standard oxygen consumption and ventilatory frequency of Stage 6 of L. fluviatilis rose from 24.3 mul g -1 h-1 and 33.0 beats min-1 at 5°C to 103.8 mul g-1 h-1 and 98.2 beats min -1 at 15°C. In contrast to larvae, metamorphosing animals displayed a circadian rhythm of oxygen consumption.
|Date of Award||1976|