gill(redirected from Physical gill)
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Zoology The respiratory organ of most aquatic animals that obtain oxygen from water, consisting of a filamentous structure of vascular membranes across which dissolved gases are exchanged.
- the respiratory organ of aquatic animals. External gills, as in tadpoles, are produced by the embryonic ECTODERM; internal gills, as in fish, are developed from the pharynx and are thus endodermal (see ENDODERM). Gills are usually well supplied with blood vessels, and interchange of oxygen and carbon dioxide takes place across the extensive surface area (see COUNTERCURRENT EXCHANGE). Gills also occur in many invertebrates, for example, in insects such as the caddis fly larva and molluscs such as oysters. Occasionally, unusual structures act as gills, for example, the walls of the rectum in certain dragonfly nymphs, water being pumped in and out via the anus.
- the spore-carrying lamellae in basidiomycete fungi, located underneath the cap or ‘pileus’.
external breathing apparatus of fish. Very susceptible to a wide range of diseases.
an infectious disease of aquarium and salmonid species of fish caused by Flavobacterium bronchiophila. Also in Crassostrea angulata caused by an iridovirus and in larval shrimp caused usually by a Leucothrix spp. bacterium. Chronic, proliferative inflammation causes the gill filaments to be swollen and may be clubbed or fused. Called also bacterial gill disease.
the following external parasites are commonly found on the gills, and elsewhere on the skin, in aquarium fish: Gyrodactylus elegans—a monogenetic fluke; Diplozoon barbi, D. paradoxum—monogenetic flukes; Ergasilus sieboldi—crustaceans. Freshly caught seahorses may carry the crustacean Argulus spp. Pond fish may carry the anchor worm Lernaea spp. These are all visible with the naked eye and can be removed manually.