Do Fish Drink?
Fish do drink water, but how they consume it depends on where they live. Water gets into a fish’s body through osmosis, the process in which water diffuses from a higher to a lower concentration.
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.
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.
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.
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.
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.
Why Do You Become Dehydrated When Sick?
When you have a cold or flu, the doctor (or Dr. Mom) may tell you to drink lots of fluids. But did they ever explain why you need to guzzle all that water and juice? The extra fluid helps prevent dehydration, which can make you feel even worse, and make it harder to get well. If you have a runny nose, a feverish sweat, or vomiting and diarrhea, it may seem obvious why you’d need to drink more to replace those lost fluids. But these aren’t the only reasons the body needs extra fluid when you’re sick.
If you have a fever, that increase in body temperature increases your metabolism–in other words, all the biochemical reactions that keep you alive speed up. A fever of 101 degrees Fahrenheit increases your body’s metabolic rate by about 10%. What difference does that make?
Two key ingredients of metabolic reactions are water and oxygen. Increased metabolism uses more water and also makes you breathe faster, to supply the extra oxygen. And guess what? As you breathe faster, you breathe out more moisture, along with more carbon dioxide.
Even if you don’t have symptoms that cause obvious water loss–like a runny nose, sweating, vomiting or diarrhea–a cold or flu can dehydrate you in hidden ways. Just a slight rise in body temperature requires more water for metabolic reactions and breathing.
On top of all that, when you’re sick you just might not feel like eating or drinking as much as usual. That’s why Mom keeps reminding you to drink your fluids!