Fish Gills

Not all animals have lungs. Many animals live in environments where lungs would be efficient enough for survival. Gills are another type of respiratory system, which are very efficient at removing oxygen from water: there is only 1/20 the amount of oxygen present in water as in the same volume of air. Gills greatly increase the surface area for gas exchange and they occur in a variety of animal groups including arthropods (including some terrestrial crustaceans), …

…activity, the larger and more active the animal the more lamellae it will have. (Evans 1998) Gills provide a one-way flow for oxygen to perfuse over them. This one way flow increases their efficiency since there is not much mixing of oxygenated and deoxygenated water directly over the gills and there is no “dead air space” such as the trachea in which oxygenated and deoxygenated water can get mixed. Bibliography Thr physiology of fishes. David Evans 1998