Gills use a countercurrent exchange system that increases the efficiency of oxygen-uptake from the water. Fresh oxygenated water taken in through the mouth is uninterruptedly "pumped" through the gills in one direction, while the blood in the lamellae flows in the opposite direction, creating the countercurrent blood and water flow (Fig. 22), on which the fish's survival depends.
Gills use a countercurrent exchange system that increases the efficiency of oxygen-uptake from the water Fresh oxygenated water t!aken in through the mouth is uninterruptedly "pumped" through the gills in one dir,ection, while the blood in the lamellae flows in the opposite direc.tion, creating the countercurrent blood and water flow (Fig. 22), on which the fish's survival depends.