Pelagic fish live near the surface or in the water column of coastal, ocean and lake waters, but not on the bottom of the sea or the lake. They can be contrasted with demersal fish, which do live on or near the bottom, and reef fish which are associated with coral reefs.[1]
The marine pelagic environment is the largest aquatic habitat on earth, occupying 1,370 million cubic kilometres (330 million cubic miles), and is the habitat for 11 percent of known fish species. The oceans have a mean depth of 4000 metres. About 98 percent of the total water volume is below 100 metres, and 75 percent is below 1000 metres.[2]
Marine pelagic fish can be divided into coastal (inshore) fish and oceanic (offshore) fish.[3] Coastal fish inhabit the relatively shallow and sunlit waters above the continental shelf, while oceanic fish (which may well also swim inshore) inhabit the vast and deep waters beyond the continental shelf.[4]
Pelagic fish range in size from small coastal forage fish, such as herrings andsardines, to large apex predator oceanic fishes, such as the Southern bluefin tuna and oceanic sharks.[1] They are usually agile swimmers with streamlined bodies, capable of sustained cruising on long distancemigrations. The Indo-Pacific sailfish, an oceanic pelagic fish, can sprint at over 110 kilometres per hour. Some tuna species cruise across the Pacific Ocean. Many pelagic fish swim in schools weighing hundreds of tonnes. Others are solitary, like the large ocean sunfish weighing over 500 kilograms, which sometimes drift passively with ocean currents, eating jellyfish.[1]
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