Salt Kills Freshwater Fish and Shuts Down Their Kidneys.
Fishing in freshwater is very different from saltwater, and for this reason the equipment you use will vary. Here’s a quick overview of each.
Saltwater fish die in freshwater due to overhydration, and freshwater fish die in saltwater due to dehydration. This seems to make little sense, given that a fish surrounded by water shouldn't die from a lack of water, but due to the physiology of a fish's skin and the natural properties of water, each type of fish is suited to their fresh or salty habitat, but no other.
To understand why saltwater fish die when placed into freshwater, we first need to understand the structure of their cells. Fish cells are semi-permeable: Some elements can pass through them, while others cannot. In the case of our finned friends, water can move back and forth through the cellular membrane, but dissolved salt in the water is too big for the membrane, and won't pass through.
Aquarium Salt Benefits Freshwater Fish - Drs. Foster and Smith
Aquarium Salt Mix: Salt for Saltwater and Freshwater Fish Aquariums
The practice of adding salt (a.k.a. Sodium Chloride, rock salt, table salt, solar salt, aquarium salt) to freshwater aquariums has been around almost as long as the hobby. There are several reasons why hobbyists add salt to the aquarium, stress reduction, medicating, adding hardness, and for fish commonly found in brackish water. It has become a common practice for employees of big box stores to tell all of their freshwater customers to add a teaspoon of salt per 10 gallons (38 l). This is not a practice most advanced hobbyist partake in, nor one recommended. Before you add salt to a freshwater aquarium, you should understand why you are doing so, and any possible side effects.Freshwater fish and plants have evolved to live in an environment that has very little salt, and because of this some are very sensitive to salt. Most freshwater plants do not tolerate much salt at all, and if you are trying to keep live plants, salt as a general rule should be avoided. Some species of fish from very soft water, like (Sucker Mouth Catfish) do not tolerate much salt either, and the addition of salt with these fish should be avoided.Most wild populations of freshwater fish and plants in the hobby come from rivers and lakes that have very little if any detectable salt. Freshwater fish are adapted to water with salt content that is measured in parts per million (ppm), versus seawater that is measured in parts per thousand (ppt). My local water supply comes from surface water and it averages less than 3 ppm total sodium. That means that out of one million parts, less than 3 are salt. In many cases freshwater has very low salt content, and in some areas of the world, like tropical rain forests, it can be so minute that it is undetectable.The dividing line between saltwater and freshwater on the rivers listed is defined in this section, and all waters of the rivers and their tributaries, streams, and estuaries lying seaward of the dividing lines are considered saltwaters, and all waters lying landward or upstream from all dividing lines are considered freshwaters for purposes of licensing and regulating commercial and recreational fishing.