MadSci Network: Zoology |
Fish get their oxygen directly from the water in which they live. So, they don't really breathe like people do by getting oxygen from air. The term "respire" is probably more accurate. Fish use their gills to obtain oxygen from the water. The gill is a very special tissue that has many, many blood vessels running through it. As water passess over the gills of a fish, oxygen from the water diffuses across the gill cell membrane and then into the blood. The blood can then carry the oxygen to the other tissues in the fish (like the muscle, the eye, the stomach, etc.). In a typical tank fish (those we keep as pets), you can usually tell if the fish is respiring by watching the opercula - the flaps on the side of the fish just behind the head. Inside the opercula are the gills. The way many fish keep water flowing over the gills when they are not moving is to use muscles to create a vacuum of sorts - one that will pull water in through the mouth and then expel it across the gills & out the opercula. So, if the opercula are moving, the fish is respiring. Fish can also use what is known as "ram ventilation" whereby they swim with the mouth open. This enables water to enter the mouth and exit through the opercula. This technique keeps fresh, oxygenated water flowing over the gills. Interestingly, there are some fish that have lungs or other structures that enable them to get their oxygen from air. A great example of this is the Beta - a very common pet fish right now. The Beta (or Siamese fighting fish) uses what is known as a labyrinth organ and needs to have access to air in order to survive. More detailed information on fish respiration can be found by visiting these sites: http://www.lookd.com/fish/respiration.html http://www.csuchico.edu/~pmaslin/ichthy/fshrsp.html http://users.northnet.com.au/~cycen/bettainfo.html http://www.exotictropicals.com/encyclo/fresh/anabantoids/labyrinth.htm Thanks for your question! Sue
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