Tips on Salt

Tips on Salt
By Dr. Kaew (Asst. Prof. Dr. Somphoth Weerakul, DVM)

Many of us hold significant misunderstandings regarding the use of salt. Ultimately, this often leads to the loss of fish because salt was used without proper knowledge. It is important to remember that salt can be both a cure and a toxin.

To understand salt, we must first understand the fish. Fish must constantly adapt to survive in their surrounding habitats. Saltwater fish live in environments where the external salt concentration is higher than that inside their bodies. Conversely, freshwater fish live in conditions where the salt concentration is lower than that of their internal fluids. (Interestingly, regardless of the habitat, the internal salt levels in most fish are relatively similar).

Diffusion and Salt Concentration
Water naturally flows from an area of low salt concentration to an area of high salt concentration. This involves the exchange of ions: Sodium with Hydrogen, and Chloride with Bicarbonate.

If this is the case, what happens?

Marine Fish: Since their internal salt levels are lower than the surrounding sea, they constantly lose water through diffusion. They face the risk of dehydration.
Freshwater Fish: Their blood salt concentration is higher than the surrounding water. Consequently, large amounts of water constantly flow into their bodies, leading to "edema" (water retention).
To survive, fish have developed several biological mechanisms:

Skin Barrier: The skin acts as a barrier to prevent the uncontrolled flow of water. But what happens when the fish is wounded? The barrier is compromised.
Gills and Kidneys: Gills are the primary site for oxygen exchange between the blood and water, making them highly permeable.

Freshwater fish constantly take in water and salt (Sodium Chloride) through their gills. Their kidneys work hard to retain salt while filtering out and excreting large volumes of water as urine.
Marine fish try to retain every drop of water. Their kidneys are less focused on salt absorption and more focused on water reabsorption, while actively excreting excess salt.
The Rectal Gland: Some saltwater species possess a "Rectal Gland" connected to the cloaca, specifically designed to eliminate excess salt from the body.
When Things Go Wrong
Disease, transport stress, water preparation, or exposure to medications and chemicals can weaken a fish. This disrupts their internal balance, known as Homeostasis. When homeostasis fails, the fish’s salt-regulation mechanisms are usually the first to suffer.

The Role of Salt in Treatment
In a therapeutic context, "salt" refers to Sodium Chloride ($NaCl$). This can be sourced from sea salt or rock salt, though sea salt is most common. Today, many use Artificial Salt (pure $NaCl$) in treatments and laboratories. Salt is incredibly beneficial, especially for freshwater fish.

Osmoregulatory Stress: Salt helps reduce stress related to electrolyte imbalances. This is particularly useful after transport, water changes, or any event that causes stress.
Antiparasitic Properties: Salt helps eliminate or inhibit protozoa, fungi, parasites, and some bacteria. (Note: It is less effective against bacteria unless used at concentrations so high the fish might not survive).
Dosage and Concentration
In pharmacology, "percent (%)" refers to grams per 100 ml.

1% Salt = 1g per 100ml (or 10g per liter).
This is quite high! You must set clear time limits for exposure. Freshwater fish lack the efficient salt-excreting mechanisms of marine fish; if kept in a 10% solution all day, they will perish.

Correct Dosage Guidelines:

Indefinite Bath (24/7): 1–5 grams per liter. This is used to eliminate some pathogens and assist in homeostasis. It reduces stress during transport or when introducing new fish. For general supportive care, keep it low—no more than 3 grams per liter.
Short Bath (30 Minutes): 10–30 grams per liter. This high concentration is used to knock off protozoa and certain external parasites. For weak fish, use the lower end of this range and repeat after 24 hours if necessary.
Dip (10 Minutes): 30 grams per liter. This is strictly for fish weighing over 100 grams.
Goldfish and Koi: These species are quite salt-tolerant. They can handle 30–35 grams per liter, but only for 4–5 minutes.
Precautions
Sensitive Species: Certain types of Catfish are highly sensitive to salt.
Overdosing: Excessive salt can be fatal or further weaken an already sick fish.
Salt has many more benefits, which I will expand upon in the future.