DISTRIBUTION
Fish are found throughout the world, from altitudes of more than 5,000 m (3 mi), as in
Lake Titicaca, located 3,800 m (2.3 mi) above sea level in the Andes, to depths of about
10 km (6 mi) in the Pacific Ocean. Some, like certain killifishes, Cyprinodon, inhabit hot
springs, where the water temperature may reach 45 deg C (113 deg F); others, like the
icefishes, Chaenocephalus, are found in Antarctic seas, where water temperature may fall
below 0 deg C (32 deg F). About 107 species, including the swordfish, Xiphias, are
distributed worldwide in tropical and subtropical waters, but many species have very
limited ranges, among the smallest being that of the killifish Cyprinodon diabolis, which
is confined to a single spring in Nevada.
About 70% of the Earth's surface is covered by oceans and seas, and about 3.5% of the land
surface (1% of the Earth's total surface) is covered by fresh water. Inhabiting these
waters are an estimated 20,000 or more fish species, equal to or exceeding the number of
all other vertebrate species combined. Bird species number approximately 8,600; reptiles,
6,000; mammals, 4,500; and amphibians, 2,500. About 60% of the fish species live in marine
waters; the remaining 40% are found in fresh water.
Most of the world's fishes are continental in orientation, living either as part of the
freshwater systems on land or as sea-dwellers staying near and influenced by the coastal
environment. High densities of marine fish populations occur near coasts, because the
waters there are extremely rich in nutrients. Coastal benefits include chemical and
organic enrichment discharged by rivers, upwellings from the ocean depths that recycle
previously deposited nitrates and phosphates, aeration caused by surf and tide, and the
penetration of sunlight.
Anatomy -
Circulation - Respiration - Air
Breathing
Body Temperature - Water
Balance - Swimming - Gas Bladder
Lateral Line System - Evolution
- Reproduction