CoachA gill is an evagination of the body surface into the water, folded into filaments and lamellae a few micrometres thick through which blood flows in capillaries. A fish’s gills hang from four bony arches on each side; water drawn in at the mouth and pushed out under the gill covers by a two-pump system flows between the lamellae in one direction, and the blood in the lamellae flows the other way: a counter-current. A trout of a kilogram has some of lamellar surface, thick.
উদাহরণ
Example 21.6 (The price of water)
A resting trout of takes about of oxygen an hour. From water at , with extraction, it must pump of water an hour across its gills — nine kilograms of a medium fifty times more viscous than air, through channels a fraction of a millimetre wide. A tenth of its metabolism goes to breathing; a human at rest spends a fiftieth. Warm the pond to and the same fish, needing more oxygen from water holding less, must pump three times as much.