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Red represents a higher value (e.g. of temperature or the partial pressure of a gas) than blue so the property being transported in the channels flows from red to blue. In fish a countercurrent flow (lower diagram) of blood and water in the gills is used to extract oxygen from the environment. [6] [7] [8] All basal vertebrates breathe with gills.
Aquaculture is the most rapidly expanding food industry in the world [7] as a result of declining wild fisheries stocks and profitable business. [2] In 2008, aquaculture provided 45.7% of the fish produced globally for human consumption; increasing at a mean rate of 6.6% a year since 1970.
It covers 11.4 million square kilometres (4.38 million sq mi), which is the second largest zone in the world, exceeding the land area of the United States. [5] According to the FAO, in 2005, the United States harvested 4,888,621 tonnes of fish from wild fisheries, and another 471,958 tonnes from aquaculture. This made the United States the ...
Worldwide, the most important fish species used in fish farming are, in order, carp, salmon, tilapia, and catfish. [28] In the Mediterranean, young bluefin tuna are netted at sea and towed slowly towards the shore. They are then interned in offshore pens (sometimes made from floating HDPE pipe) [40] where they are further grown for the market. [41]
The flow rate necessary to maintain water quality can also change through the year, as the temperature changes and the cultured species grow larger. For reason such as these, continuous monitoring of water quality is important, including measurements of water flow rates, pH levels and temperature, as well as the levels of dissolved oxygen, and ...
In this system, of both local and imported fish, a combination of five or six fish species is used in a single fish pond. These species are selected so that they do not compete for food among them by having different types of food habitats. [34] [35] As a result, the food available in all the parts of the pond is used. Fish used in this system ...
The rete mirabile utilizes countercurrent blood flow within the net (blood flowing in opposite directions) to act as a countercurrent exchanger. It exchanges heat , ions , or gases between vessel walls so that the two bloodstreams within the rete maintain a gradient with respect to temperature , or concentration of gases or solutes .
Some species of sharks use this system. When they swim, water flows into the mouth and across the gills. Because these sharks rely on this technique, they must keep swimming in order to respire. Bony fish use countercurrent flow to maximize the intake of oxygen that can diffuse through the gill. Countercurrent flow occurs when deoxygenated ...