Distribution

Bony fishes inhabit almost every body of water. They are found in tropical, temperate, and polar seas as well as virtually all fresh water environments.

Some species of bony fishes live as deep as 11 km (6.8 mi.) in the deep sea. Other species inhabit lakes as high as 5 km (3.1 mi.) above sea level.

About 58% of all species of bony fishes (more than 13,000 species) live in marine environments. Although only 0.01% of the earth's water is fresh water, freshwater fishes make up about 42% of fish species (more than 9,000 species).

Habitat

Bony fishes live in fresh water, sea water, and brackish (a combination of fresh water and salt water) environments. The salinity of sea water is about 35 ppt (parts per thousand). Some species can tolerate higher-salinity environments. Some species of gobies can tolerate salinity levels as high as 60 ppt.

Fishes live in virtually all aquatic habitats. Different species of fish are adapted for different habitats: rocky shores, coral reefs, kelp forests, rivers and streams, lakes and ponds, under sea ice, the deep sea, and other environments of fresh, salt, and brackish water.

• Some fish are pelagic: they live in the open ocean. For example, tunas (several species in the family Scombridae, subfamily Thunninae) are pelagic fishes.
• Some species, such as the flatfishes (order Pleuronectiformes) are adapted for living along the bottom. Certain fishes, such as gobies (family Gobiidae) even burrow into the substrate or bury themselves in sand.
• Ocean sunfish (family Molidae) are most often spotted at the ocean's surface.
• Some lungfishes "hibernate" throughout a summer drought season, buried under the mud of a dried-up pond.
• Several fish species live in freshwater habitats in the darkness of caves.
• Depending on the species, bony fishes can live at various temperatures. Some live at extreme temperatures.
• Some desert pupfish (Cyprinodon macularius) live in California hot springs that reach temperatures greater than 45°C (113°F).
• At the opposite extreme, some species of bony fishes can survive freezing temperatures of the Arctic and Antarctic. Certain glycoprotein molecules present in the blood of these specially-adapted fishes lower the freezing point of the blood. The arctic cod (Boreogadus saida) can survive temperatures as low as -2°C (28°F).

In general, fishes rely on oxygen dissolved in water for respiration.

Some species of bony fishes require large amounts of dissolved oxygen. The brown trout (Salmo trutta) requires up to 11 mg of dissolved oxygen per liter (11 ppm, or parts per million).

Misgurnus fossillis, a type of loach, can survive in water with an oxygen concentration as low as 0.5 mg per liter (0.5 ppm).

Mudskippers (family Periophthalmidae) can carry a small amount of water in their gill cavities. They commonly spend time on land, returning to mud holes when their water supply begins to evaporate.

African lungfishes (subclass Dipnoi) gulp air into a "lung" for respiration. In fact, these fishes must have access to the water's surface or they will drown.

Migration

Most bony fishes have small home ranges.

Some species of bony fishes migrate great distances. Food and habitat availability, reproduction, environmental cycles and temperature change may be causes of migration for some species.

• Almost all tuna species are migratory. Albacore (Thunnus alalunga) migrate across the Pacific Ocean from the coast of California to the coast of Japan, more than 8,500 km (5,270 mi.). Data from albacore tagging studies indicate that they travel an average of 26 km (16 mi.) per day. Tagged northern bluefin tuna (Thunnus thynnus) have migrated 7,700 km (4,774 mi.) across the Atlantic Ocean in 119 days, about 65 km (40 mi.) per day.
• Billfishes (family Istiophoridae) are highly migratory. A black marlin (Makaira indica) that was tagged and released off Cabo San Lucas, Mexico, was recovered off Norfolk Island in the South Pacific, more than 10,680 km (6,622 mi.) away.
• Some bony fish species are diadromous: they migrate between fresh and marine environments.
• Some fish are catadromous: they live in freshwater environments but migrate downriver to the ocean to spawn. The freshwater eels (family Anguillidae) develop in marine environments then move into freshwater rivers to live.
• Anadromous fishes live most of their lives in the ocean, but migrate into freshwater environments to spawn. The sockeye salmon (Oncorhynchus nerka) may travel more than 3,600 km (2,232 mi.) up the Yukon River to spawn.