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General
Fish Information
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Ichthyology is the study of fishes. Fishes are aquatic, cold-blooded
animals that have backbones and have fins and gills throughout
life. This definition covers a wide variety of species and,
consequently, a great diversity of forms and habits. Currently
recognized as valid are about 25,000 extant species of fishes
divided into 57 orders and 482 families. The number of species
of fishes exceeds all other species of vertebrates combined.
Although over 97% of the surface water on earth is saltwater,
about 41% of all species of fishes live in freshwater. The large
number of freshwater fishes is a product of the propensity for
populations in freshwater bodies to become isolated, and then
to differentiate and, eventually, speciate.
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