Water gets into a fish's body through osmosis, the process in which water diffuses from a higher to a lower concentration.
水通过渗透作用进入鱼儿的身体，在这一过程中，水从高浓度的地方扩散至低浓度的地方。
For example, if there is more water outside of a cell than inside, water will try to flow into the cell until there is the same concentration of water on either side of the cell's membrane. The body of a fish acts the same way, either absorbing or losing water depending on its surroundings.
比方说，如果细胞外的水多于细胞内，水就会流入细胞内，直到细胞膜内外的浓度相同。鱼儿的身体与细胞一样，吸水还是失水取决于它生存的环境。
Whether a fish absorbs or loses water is based on the fact that all fish must maintain a certain amount of salt in their bodies to stay healthy. Fish that live in fresh water have a higher concentration of salt in their bodies than the surrounding water.
不管鱼儿吸水还是失水，事实上，所有的鱼要想保持健康其体内就必须维持一定量的盐分。淡水鱼体内盐的浓度要高于周围的水。

Consequently, water continuously flows into the fish's body to attempt to dilute the amount of salt in the fish until it is equal to the amount of salt in the surrounding water. Since fish cannot allow their salt content to be diminished, their kidneys work overtime to expel excess water in the form of urine.
因此，水就不断地进入鱼儿的体内以稀释盐份，直到鱼儿体内与外界的盐的浓度持平。因为鱼儿自身无法减少体内的盐分，所以他们的肾就要不断工作以将多余的水以尿液的形式排出体外。
Ocean fish have the opposite problem. Surrounded by salt water, their bodies contain a relatively lower concentration of salt than the ocean water. In this case, osmosis causes the fish to constantly lose water in order to equalize salt concentration inside and outside the fish.
海鱼的问题则恰恰相反。由于被盐水包围，他们体内盐的浓度与海水相比相对较低。在这种情况下，渗透作用使得鱼儿不停地失水以平衡体内外盐的浓度。
To partially compensate for the water loss, ocean fish actually drink water through their mouths. To get rid of the excess salt they take in by drinking seawater, they excrete some salt through cells in their gills.
为了补偿失去的部分水分，海水鱼通常要用嘴喝水。而为了去除喝海水带来的多余盐分，它们会通过腮里的细胞排出一些盐分。