09-06-2007, 07:40 AM
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Most people don't even know what salt actually does for fish and I know it doesn't even say so on most product containers. You wiull often hear that salt improves gill function or adds electrolytes or reduces stress, etc...and that is all true to an extent. The main purpose of salt though is for Osmoregulation...
The cells in a fish's body have a certain salinity level inside them, just like our cells do. The water outside of the fish normally has less salt density than the cells. Because the cell walls are permeable, the fish continually "leaks" out salt into the water. In order to compensate, the fish consumes a large quantity of water to get that salt back. There are also sodium ion pumps in the cell walls that continually have to bring salt back in. All in all, the fish is always expending a certain ammount of energy to maintain a specific salt level in its body.
When you add salt to the tank, you raise the salinity of the water and therefore the fish does not "leak" as much salt. The fish can therefore conserve energy which can boost the immune system, reduce stress and improve respiratory function. I like to compare it to how us humans will lay in bed when we get sick. This allows our bodies to use all of its energy to fight off disease and is why salt is often suggested for treating disease in fish. In salt water tanks you do the opposite. Saltwater fish are constantly taking in salt because the salinity outside the fish is greater than inside the fish cells. The saltwater fish have to expend energy to expell excess salt so when saltwater fish get sick you often lower the salinity of the tank.
That being said, there are pros and cons to using salt. I personally only use it when I have a fish that seems ill or stressed. This is because while it is good for us to lay in bed when we are sick, no doctor will ever tell you to lay in bed 24 hours a day for the rest of your life! If you did that, you may be exposed to less diseases but your immune system, circulatory system and respiratory system would become weaker because it doesn't get a workout. I think using salt at all times can actually create weaker fish and I think the salt is more effective at treating disease when it is not used all the time.