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Water gets into a fish's body through osmosis, the process in which water diffuses from a higher to a lower concentration.
水通過滲透作用進入魚兒的身體，在這一過程中，水從高濃度的地方擴散至低濃度的地方。
For example, if there is more water outside of a cell than inside, water will try to flow into the celluntil there is the same concentration of water on either side of the cell's membrane.
比方說，如果細胞外的水多于細胞內，水就會流入細胞內，直到細胞膜內外的濃度相同。
The body of a fish acts the same way, either absorbing or losing water depending on its surroundings.
魚兒的身體與細胞一樣，吸水還是失水取決于它生存的環境。
Whether a fish absorbs or loses water is based on the fact that all fish must maintain a certainamount of salt in their bodies to stay healthy.
不管魚兒吸水還是失水，事實上，所有的魚要想保持健康其體內就必須維持一定量的鹽分。
Fish that live in fresh water have a higherconcentration of salt in their bodies than the surrounding water.
淡水魚體內鹽的濃度要高于周圍的水。
Consequently, water continuously flows into the fish's body to attempt to dilute the amount ofsalt in the fish until it is equal to the amount of salt in the surrounding water.
因此，水就不斷地進入魚兒的體內以稀釋鹽份，直到魚兒體內與外界的鹽的濃度持平。
Since fish cannotallow their salt content to be diminished, their kidneys work overtime to expel excess water in theform of urine.
因為魚兒自身無法減少體內的鹽分，所以他們的腎就要不斷工作以將多余的水以尿液的形式排出體外。
Ocean fish have the opposite problem.
海魚的問題則恰恰相反。
Surrounded by salt water, their bodies contain a relativelylower concentration of salt than the ocean water.
由于被鹽水包圍，他們體內鹽的濃度與海水相比相對較低。
In this case, osmosis causes the fish toconstantly lose water in order to equalize salt concentration inside and outside the fish.
在這種情況下，滲透作用使得魚兒不停地失水以平衡體內外鹽的濃度。
To partially compensate for the water loss, ocean fish actually drink water through their mouths.
為了補償失去的部分水分，海水魚通常要用嘴喝水。
To get rid of the excess salt they take in by drinking seawater, they excrete some salt throughcells in their gills.
而為了去除喝海水帶來的多余鹽分，它們會通過腮里的細胞排出一些鹽分。
