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Respiration In Fish

Date : Thursday, April 22, 2010

Fish being an aquatic animal, has a respiratory system that is different from that of animals that live on land. It is capable of breathing under water without making frequent trips to the surface to breathe air like marine mammals such as the Whale. This is due to the fact that fishes have a breathing organ known as gills. This is made up of thin feathery sheets of tissue membrane containing many blood vessels through which oxygen passes allowing fishes to breathe.
The process begins by water in the fish’s surrounding entering its mouth‘s. Water enters the mouth by a very effective pumping system that involves the mouth and the outer flexible bony flap that cover the gills called the operculum. This is achieved by the opening and closing of the fish's mouth as it pumps water through the gills. When the fish’s mouth is open, the operculum closes and water is drawn into the fish’s mouth. Conversely, when the fish closes its mouth, the operculum opens and fresh water is then allowed to flow across the gills.

After water enters the fish's mouth it passes through a structure called the gill rakers.

The function of the gill rakers is to act as a filter system by sieving out particles such as food or any other foreign particles that may have entered the mouth from the inflow of water. The filtered water then travel through the gill arches thus passing over the gills. Here each gill consists of two rows of extremely thin membranes called gill filaments. The structure of the gill filaments consist of sequence rows of a thin, disc-like membrane loaded with a capillary network called lamellae. Gill filaments which are projected out into the water flow allows water to flow across the lamellae. This will result in gas exchange where, oxygen and carbon dioxide are exchanged directly across the capillary membrane.As water flows through the gills, the oxygen it contains (dissolved oxygen) passes into blood circulating through the gill structures (filaments and lamellae) while simultaneously, carbon dioxide ( the waste product) in the fish’s bloodstream passes into the water. This deoxygenated water is then carried away and out of the body through the operculum. This process repeats itself continually and this is the process by which fish breathe. This is process is also known as respiration.

Where do fish get their oxygen from?

Water is formed from the combination reaction of hydrogen gas (H2) and oxygen gas (O2) to produce liquid water (H2O). In other words, each molecule of water is made up of two hydrogen atoms and one oxygen atom. However the oxygen that fish breath is not the oxygen found in H2O - the molecular formula of water. The oxygen in liquid water is bound to two hydrogen atoms forming water molecules, thus oxygen from is not free to take part in respiration. Therefore the fish cannot breathe the resulting liquid water, and the oxygen gas (O2) that the fish breaths comes from that which is dissolved in the water. Hence, fish "breathe" the dissolved oxygen out of the water using their gills. This also means that if there is not enough dissolved oxygen in the water, then the fish can suffocate, just as humans and other animals will if there is not enough oxygen in the air that we breathe.

Geraldine Lee(10):)

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