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| Do fishes drink water? At first glance this might seem like a very strange question. As strange as asking “Do land animals breathe air?” However eating or drinking and breathing are two different things. |
Saturday 27 July 2013
Do fishes drink Water?
All living things need to take in water in order to survive. This is very obvious for all land animals. Fishes too need to have the amount of water in their bodies at appropriate levels. Too little or too much water in their bodies would cause problems. The correct answer to this question would differ depending on whether the fish was a freshwater or saltwater one. |  A Salmon Swimming Upriver |
A freshwater fish lives in an environment which has a lower concentration as compared to the blood of the fish. Water from the surroundings would constantly move through the skin and gills of a freshwater fish and into its body. This process where water moves from an area of lower concentration to an area of higher concentration is known as Osmosis. Due to this the freshwater fish does not need to actively drink water. In fact its kidneys have to work constantly to remove the excess water otherwise the salt concentrations in the fish will drop dangerously low. A saltwater fish on the other hand is faced with a situation which is quite the opposite. Now the salt concentration in its body is lower than its environment. The fish constantly loses water through its skin and must therefore actively drink water to ensure that its body has sufficient water. The kidneys now do not do much work and in certain types of saltwater fishes they are absent. However the fishes have other ways of removing the excess salt that has entered into their bodies due to their constant drinking of water. |
 The Dangerous Swim Upriver | The bodies of fishes have therefore adapted to their environment. Freshwater fishes will die if placed in saltwater and saltwater fishes will die if placed in fresh water. How then do salmon do it? |
A salmon is born in a freshwater environment usually high up in mountains where rivers originate. They swim down to the sea where they mature into adults. They then swim back up the river facing various dangers and overcoming many hurdles until they reach the place of their birth. Those fish that survive this journey reproduce and then die. These amazing fish have to adapt twice in their life cycle to changing environments. They do this by changing their bodies to adapt first to the saltwater and then back again to freshwater. George Ferrao |