I am still being asked about the use of sodium chloride salts (table salt or commercially available aquarium salt) to aid freshwater fish specimens recover from a variety of diseases and general injuries. Unless certain protozoal diseases are involved, I generally recommend against the use of salt baths or the addition of salt to freshwater aquariums.
The following is a modification of an earlier thread I authored regarding the use of these salts in freshwater systems. With our new illness and disease subsection, I hope this post may assist in understanding some of the risks associated with sodium chloride use.
This discussion is geared towards the addition of salt to the average freshwater specimen tanks that would not ordinarily promote higher salinity. Brackish/semi-brackish live bearer tanks or those that require higher levels of general hardness (GH) including African Rift Lake cichlids are a distinct issue and merit their own discussion. The GH needs of African cichlids in particular require a salt balance totally unrelated to the addition of the sodium chloride salts discussed here. For African rift tanks, hard ions (such as the magnesium provided by Epsom salt) are required. There are no naturally occurring aquatic environments which have high sodium salinity with simultaneously low hardness due to low calcium/magnesium ion concentrations.
Some advocate for the addition of sodium chloride salts (typically at a concentration of 1 tablespoon per 5 gallons of water) to create benefits for fish specimens and aid in recovery. Let's examine these below:
____________________
I heard that salt can inhibit nitrite toxicity...
Salt can minimize nitrite poisoning by inhibition of nitrite ion uptake if chloride concentration is ~30 times greater than that of nitrite by sequestration of anion binding membrane transport. Assuming a toxic nitrite level of 0.1 ppm, this would require an estimated chloride concentration of ~3 ppm. A mere 1 teaspoon of salt would be sufficient to provide this desirable effect for ~300 gallons of tank water; contrast this to the typical recommendation for salt addition per gallon (1 tbsp/gallon).
____________________
Doesn't salt reduce osmotic pressure and stress?
The addition of salt electrolytes can reduce osmotic stress for the gills. The ability of the fish to maintain homeostasis with its surrounding water is disturbed during times of stress or disease. Equilibrating this gradient provides ‘relief’ for specimens. The osmotic pressure in question is not ion specific and is comprised of the total ionic potential of a many ions in solution including magnesium (Mg), calcium (Ca), chloride (Cl), sodium (Na), potassium (K), etc. The sodium and chloride contribution of salt addition represents only a fraction of the total osmotic potential for tank water of average tank hardness (i.e. GH). Mg and Ca are far more important in this pressure system than either Na or Cl. Excessive gradients can lead to disruption of membrane potentials for specimens both at the gill membrane and at other ionic exchange membranes. Finding this balance is very difficult.
____________________
But salt promotes slime coat and speeds wound healing...
Salinity promotes the creation of slime coat in many fish. This coat assists in the clearance of scale-bound parasites and helps cope with other disease states. Many (if not all) commercially available water conditioners already provide for ample stimulation of this coat. Wound healing may occur via the created osmolar gradient. If the surrounding water has a higher concentration of total dissolved solids (TDS) than the fluids circulating within the fish, fluids move away from the wound site. Fresh plasma moves in response to the displacement, promoting flow to the wound area and augmenting immune response via migration of immune cells to site of injury. There is also a significant risk of osmotic stress directly across already fragile and friable fish tissue membranes if the TDS osmolar gradient is too large. This is especially dangerous in the context of the high TDS "salt bath". Plasma seepage or hemorrhage can occur in extreme cases as a result of tissue disruption (just as it can in humans).
____________________
What about salt for protozoal diseases like ich (aka white spot)?
Many pathogens including ichthyophthirius do not tolerate higher concentrations of salinity. In conjunction with an increase in temperature to accelerate the protozoan’s life cycle, increased salinity is often all that is necessary to turn the tide against the disease. Salt is a welcome ally in the war against dreaded “white spot” and in this configuration, is treated as a medicinal additive. Appropriate treatment regimens also call for large water changes to remove this excess salt upon conclusion of the treatment. Note that in this context salt is used as a medicine, not as a regular tank additive.
____________________
But I've used salt for years and never had any problems...
Sodium salts may have an unpredictable effect on many specimens. Some fish seem unaffected by its addition while others show instant signs of irritation. If not predissolved before addition, salt can generate serious burns. This is an important consideration for scaleless fish including certain species of loach, catfish and freshwater eels. As mentioned, sodium chloride raises the total dissolved solid (TDS), GH and the important osmolar gradient of water. For those with average general tank hardness, this addition is less significant due to the presence of the other TDS ions previously listed (specifically Ca and Mg). However, for those with softer tank water, the addition of salt can have a profound impact. Many fish specimens generally do not thrive in waters of higher TDS including wild-caught (and to a lesser extent tank-raised) fish from the Amazon basin. Discus, tetra, corydoras etc. owners should be aware of this dynamic. Freshwater fish are highly adaptable creatures but immersion in solutions of high (or low) TDS can have serious consequences for many species.
____________________
My LFS uses salt baths all the time!
It is difficult for the average aquarist to create a balance between an osmolar gradient that will assist the fish vs. one that can actually promote stress. Inherent variability from one species to another (even one specimen to another) also means that a single recommendation for level of "therapeutic salt" is impossible to establish. Salt baths (with much higher added salt concentrations) place fish in environments of increased TDS and GH for brief periods of time. This is an extremely stressful event for an already stressed specimen. Such baths are often promoted for the treatment of edema (aka dropsy). The renal (kidney) and hepatic (liver) failure often associated with this condition makes the fish especially susceptible to imbalances in osmotic regulation; if the bath itself helped to alleviate some of the edema, the switch back to regular tank water (at lower TDS) in itself represents another environmental challenge. The primary goal should be to treat the underlying cause (e.g. bacterial infection) whenever possible and not to merely palliate manifestations or symptoms of the disease. We all strive for consistency in the aquatic environment whenever possible.
____________________
In conclusion, there is little compelling evidence supporting or validating the addition of sodium salt (or use of salt bath) for anything other than a recognized medicinal purpose (e.g. protozoal disease). There are no existing guidelines for its safety or efficacy. There is no compelling evidence strongly in support of its addition (nor are there any situations calling for its absolute contraindication). The regular use of salt in the aquarium may be associated with disproportionately more harm than good. Striking a balance between potentially beneficial osmolar gradients versus those capable of promoting fish injury is difficult, is subject to inter-species variability, and represents additional stress for the specimen in the context of a high TDS bath. Sodium salts should be treated as a welcome medicinal in the arsenal against protozoal disease, not as an additive for an otherwise stable aquatic environment nor for general recovery from illness.
The following is a modification of an earlier thread I authored regarding the use of these salts in freshwater systems. With our new illness and disease subsection, I hope this post may assist in understanding some of the risks associated with sodium chloride use.
This discussion is geared towards the addition of salt to the average freshwater specimen tanks that would not ordinarily promote higher salinity. Brackish/semi-brackish live bearer tanks or those that require higher levels of general hardness (GH) including African Rift Lake cichlids are a distinct issue and merit their own discussion. The GH needs of African cichlids in particular require a salt balance totally unrelated to the addition of the sodium chloride salts discussed here. For African rift tanks, hard ions (such as the magnesium provided by Epsom salt) are required. There are no naturally occurring aquatic environments which have high sodium salinity with simultaneously low hardness due to low calcium/magnesium ion concentrations.
Some advocate for the addition of sodium chloride salts (typically at a concentration of 1 tablespoon per 5 gallons of water) to create benefits for fish specimens and aid in recovery. Let's examine these below:
____________________
I heard that salt can inhibit nitrite toxicity...
Salt can minimize nitrite poisoning by inhibition of nitrite ion uptake if chloride concentration is ~30 times greater than that of nitrite by sequestration of anion binding membrane transport. Assuming a toxic nitrite level of 0.1 ppm, this would require an estimated chloride concentration of ~3 ppm. A mere 1 teaspoon of salt would be sufficient to provide this desirable effect for ~300 gallons of tank water; contrast this to the typical recommendation for salt addition per gallon (1 tbsp/gallon).
____________________
Doesn't salt reduce osmotic pressure and stress?
The addition of salt electrolytes can reduce osmotic stress for the gills. The ability of the fish to maintain homeostasis with its surrounding water is disturbed during times of stress or disease. Equilibrating this gradient provides ‘relief’ for specimens. The osmotic pressure in question is not ion specific and is comprised of the total ionic potential of a many ions in solution including magnesium (Mg), calcium (Ca), chloride (Cl), sodium (Na), potassium (K), etc. The sodium and chloride contribution of salt addition represents only a fraction of the total osmotic potential for tank water of average tank hardness (i.e. GH). Mg and Ca are far more important in this pressure system than either Na or Cl. Excessive gradients can lead to disruption of membrane potentials for specimens both at the gill membrane and at other ionic exchange membranes. Finding this balance is very difficult.
____________________
But salt promotes slime coat and speeds wound healing...
Salinity promotes the creation of slime coat in many fish. This coat assists in the clearance of scale-bound parasites and helps cope with other disease states. Many (if not all) commercially available water conditioners already provide for ample stimulation of this coat. Wound healing may occur via the created osmolar gradient. If the surrounding water has a higher concentration of total dissolved solids (TDS) than the fluids circulating within the fish, fluids move away from the wound site. Fresh plasma moves in response to the displacement, promoting flow to the wound area and augmenting immune response via migration of immune cells to site of injury. There is also a significant risk of osmotic stress directly across already fragile and friable fish tissue membranes if the TDS osmolar gradient is too large. This is especially dangerous in the context of the high TDS "salt bath". Plasma seepage or hemorrhage can occur in extreme cases as a result of tissue disruption (just as it can in humans).
____________________
What about salt for protozoal diseases like ich (aka white spot)?
Many pathogens including ichthyophthirius do not tolerate higher concentrations of salinity. In conjunction with an increase in temperature to accelerate the protozoan’s life cycle, increased salinity is often all that is necessary to turn the tide against the disease. Salt is a welcome ally in the war against dreaded “white spot” and in this configuration, is treated as a medicinal additive. Appropriate treatment regimens also call for large water changes to remove this excess salt upon conclusion of the treatment. Note that in this context salt is used as a medicine, not as a regular tank additive.
____________________
But I've used salt for years and never had any problems...
Sodium salts may have an unpredictable effect on many specimens. Some fish seem unaffected by its addition while others show instant signs of irritation. If not predissolved before addition, salt can generate serious burns. This is an important consideration for scaleless fish including certain species of loach, catfish and freshwater eels. As mentioned, sodium chloride raises the total dissolved solid (TDS), GH and the important osmolar gradient of water. For those with average general tank hardness, this addition is less significant due to the presence of the other TDS ions previously listed (specifically Ca and Mg). However, for those with softer tank water, the addition of salt can have a profound impact. Many fish specimens generally do not thrive in waters of higher TDS including wild-caught (and to a lesser extent tank-raised) fish from the Amazon basin. Discus, tetra, corydoras etc. owners should be aware of this dynamic. Freshwater fish are highly adaptable creatures but immersion in solutions of high (or low) TDS can have serious consequences for many species.
____________________
My LFS uses salt baths all the time!
It is difficult for the average aquarist to create a balance between an osmolar gradient that will assist the fish vs. one that can actually promote stress. Inherent variability from one species to another (even one specimen to another) also means that a single recommendation for level of "therapeutic salt" is impossible to establish. Salt baths (with much higher added salt concentrations) place fish in environments of increased TDS and GH for brief periods of time. This is an extremely stressful event for an already stressed specimen. Such baths are often promoted for the treatment of edema (aka dropsy). The renal (kidney) and hepatic (liver) failure often associated with this condition makes the fish especially susceptible to imbalances in osmotic regulation; if the bath itself helped to alleviate some of the edema, the switch back to regular tank water (at lower TDS) in itself represents another environmental challenge. The primary goal should be to treat the underlying cause (e.g. bacterial infection) whenever possible and not to merely palliate manifestations or symptoms of the disease. We all strive for consistency in the aquatic environment whenever possible.
____________________
In conclusion, there is little compelling evidence supporting or validating the addition of sodium salt (or use of salt bath) for anything other than a recognized medicinal purpose (e.g. protozoal disease). There are no existing guidelines for its safety or efficacy. There is no compelling evidence strongly in support of its addition (nor are there any situations calling for its absolute contraindication). The regular use of salt in the aquarium may be associated with disproportionately more harm than good. Striking a balance between potentially beneficial osmolar gradients versus those capable of promoting fish injury is difficult, is subject to inter-species variability, and represents additional stress for the specimen in the context of a high TDS bath. Sodium salts should be treated as a welcome medicinal in the arsenal against protozoal disease, not as an additive for an otherwise stable aquatic environment nor for general recovery from illness.
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