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Fish Application Software Download Free Android Application software download free Android A fish (plural: fishes) is an aquatic vertebrate with a backbone, a skull, and gills that are used to breathe. Fish are found in every ocean, river, and lake on Earth and can be eaten or raised as food for humans. They are also commonly raised as ornamental fish in ponds or aquariums, and some are kept as pets. Despite their wide diversity, many fish have evolved similar characteristics to allow them to survive in the same environment. This makes them very effective at obtaining food and avoiding predators. Although scientists do not always agree on the exact definition of a fish, it is generally defined as any non-tetrapod craniate animal that has gills throughout its life and that has fins. The term is often applied to any ray-finned fish, even though hagfishes, lampreys, sharks, and rays are closer relatives of tetrapods (amphibians, reptiles, birds, and mammals) than they are to lobe-finned fish. Most fish are oviparous, that is, their eggs develop outside the mother's body. A few fish are ovoviviparous, however, in which case the male delivers sperm to the female's genital opening using a pair of modified pelvic fins called claspers. Most fish exchange gases by pulling oxygen-rich water in through openings on either side of the pharynx and pushing carbon dioxide-poor water out through the gills. This countercurrent flow is important for extracting oxygen from the water and eliminating carbon dioxide from the blood. The gills are covered by a protective bony covering, known as an operculum. Starfish, jellyfish, and crayfish, which are sometimes mistaken for fish, do not have this feature and are instead echinoderms or cnidarians (see Exploring Our Fluid Earth) that are related to sea urchins and corals, respectively.
