Salt Water and Amphibians?

Freshwater has the tendency to move from environments with low salt concentrations to ones with high, through a process called osmosis. This process is synonymous with the tendency of water to spread out and dilute its surroundings. If an animal cell were placed in a solution with a lower salt concentration than inside the cell itself, the cell would gain water by osmosis, and swell. This is why deionized or distilled waters cause internal problems when used with amphibians (see more on distilled water below). Conversely, if an animal cell were placed in a solution of higher concentration of salts than inside the cell, the cell would lose water to the outside environment, causing the cells to become flaccid. To avoid salt concentration disruptions in the cells, animals must always be bathed in solutions with nearly the same salt concentration as that found within their cells. Osmoregulation, a homeostatic function performed by the hypothalamus, allows animal kidneys to remove excess salts, within a moderate degree, allowing a small margin of differentiation between the salt concentration inside and outside the cell. The whole concept is rather intuitive, for most people know that the majority of plants and animals found in the ocean will die if placed in freshwater, and vice versa. It is very important to keep aquatic and semi-aquatic animals within the correct salinity levels, otherwise the salt balance of external water and internal cell construct is disrupted, resulting in poor health and/or the death of the animal. This is especially true with amphibians, as they possess semi-permeable skin and are very sensitive to their surrounding environment. 

It is also worth noting that salt concentrations affect the pH of a water solution; another reason why salt concentrations in freshwater environments are important factors when keeping captive animals. For more information on pH, water chemistry, and the nitrogen cycle, see article 0009 - Introduction to the Nitrogen Cycle.

So, if freshwater has salt in it, what's the difference between saltwater, as in the ocean, and freshwater? Well, terminology, composition, and the amount of salt, really. Saltwater is a term used to describe highly saline waters, and is used broadly to describe the ocean. Technically, all natural water sources are saltwater in the sense that they contain salts, but differ in possessing varying degrees of salts, and different types of salts. The term freshwater is typically used to describe water sources with a dissolved salt content of less than 1,000 ppm (parts per million), which equals .100%. In contrast, highly saline waters, usually referred to as saltwater, consist of dissolved salt contents from 10,000 ppm or higher, or 1.00% or higher. The ocean is at the high level, with 3.50% dissolved salt content. There are other classifications in between the high and low, namely slightly saline levels (.100%-.300%), and moderately saline levels (.300%-1.00%). The term freshwater has been applied to nearly every water source except the oceans. The terms saltwater and freshwater are a bit ambiguous, as they are sometimes used strictly to differentiate between the ocean and all other forms of water, but are also used to differentiate between the general salinity of a given water body, whether it be sea water or not. 

Despite the ambiguity of the terms freshwater and saltwater, it is important to know that the oceans are different from all other water bodies on the planet. The oceans, formed some 4.6 billion years ago, are unique in being one of the oldest entities on the planet. The oceans were formed when atmospheric Oxygen and Hydrogen condensed as primordial Earth began to cool, and they've been here ever since. Freshwater systems, on the other hand, have come and gone throughout the course of life on Earth, and have been formed from various events, such as melting glaciers during and just after the ice age ("glacial scour"), volcanic activity, tectonic movements, and seepage from layers of soluble rock. The oldest lakes on the planet today only date back around 10,000 years or so. So, in terms of composition, "freshwater" and "saltwater" are layman terms used to describe different concentrations of salts in water systems, but there is a significant, geological difference between the oceans and our freshwater systems. 

Amphibians are generally associated with freshwater systems, with the exception of a few species that tolerate brackish (moderately saline) waters or inhabit the marine biome. The chemical composition of freshwater systems brings us to the focus of this article, creating suitable water sources for captive amphibians. Now that we know there are ions (salts) present in freshwaters to varying degrees, the following sections on de-ionized, spring, and conditioned waters should make sense.

Unsafe Types of Water for Captive Amphibians

One might argue that de-ionized water accumulates ions when exposed to the atmosphere, which is absolutely correct, however this is still unsafe for use with amphibians. After a few minutes of exposure, a liter of de-ionized water accumulates only a very small amount of ions, resulting in soft water and acidic pH (usually around 5.6). Most amphibians should be kept around pH 7.0, with a few species preferring pH as low as 6.8 or as high as 7.8. The accumulation of ions from the atmosphere is not sufficient enough to raise the pH of de-ionized water to a safe level, and thus should not be used alone with aquatic or semi-aquatic amphibians. De-ionized water is often used to mist or spray terrestrial amphibians, under the pretense that the water will collect ions from the surrounding terrain. Again, this method is used often, and some would argue the safety of using de-ionized water just for misting purposes, for the fore mentioned reasons.

It is also a fallacy that boiling tap water creates distilled water. Although the distilling process does include boiling at some point, the entire process is more complex and consists of several additional steps to completely remove all ions from the water. Boiled water is similar to distilled water in that some salts and minerals are removed from it, however, boiling alone does not evaporate all present substances. Boiling tap water will kill some bacteria, and evaporate some chemicals, but not all of them because some chemicals do not vaporize at the boiling point of H₂O (100șC). Because of this, boiled tap water is not a safe method for pre-treating water for amphibians.

Acceptable Types of Water for Captive Amphibians

The majority of water sources in the US and other countries are treated with harmful chemicals to kill bacteria, and meet the standards for human consumption. If you're interested in what's in your tap water, you can contact your county or city water district for more information. Keep in mind, that the water sources may not be the same in different cities and counties; some may have extremely hard water, and some may have very soft water, both of which will affect the pH of the water. Many rural cities may have well water, which may or may not be treated with bacteria-inhibiting chemicals. For more information about hard water, soft water, and pH, see article 0009 - Introduction to the Nitrogen Cycle.

Spring water, usually in conjunction with harder water, can also be used. Spring water is extracted from underground formations in which water flows naturally to the surface of the Earth. Spring water is still treated to remove any harmful substances before human consumption, but in order to be defined as spring water, it must retain the same chemical composition and quality as the natural water source. In other words, spring water does not possess the added substances present in tap water, and still contains the minerals and salts that are removed from de-ionized water. Because spring water retains its original chemical properties, it will not disrupt the chemical makeup of most amphibian cells. One drawback of spring water is that is typically soft, which means it tends to have a pH on the low side (acidic). This can be detrimental to certain aquatic species that require neutral, or even slightly alkaline (hard) water to maintain good skin health. Spring water is typically not used by itself, but in some ratio with hard water, usually tap water treated with a water conditioner, to create a neutral (pH of 7.0) solution. Of course, there are other methods to offset the low pH of soft water; for more information about hard water, soft water, and pH, see article 0009 - Introduction to the Nitrogen Cycle.  

Like soft spring water, de-ionized, distilled, or RO water sources can also be used in some ratio with conditioned tap water to obtain a healthy level of ions (i.e. harness or softness of the water), and lower or raise the pH. 

Clean pond water can also be used with amphibians. Pond water contains a wealth of living organisms, which can provide a source of food for larvae and small amphibians, in addition to supplemental foods such as daphnia, copepods, scuds, and chopped tubifex worms. Keep in mind, however, that collected pond water can introduce harmful microbes, parasites, bacteria, or other agents, so the use of pond water may pose some health risks.

Some may opt to create their own water/salt solutions using distilled water and various salt mixtures. This eliminates the need for water conditioners, and allows keepers to control the pH level by adjusting the softness/hardness of the water accordingly. Table 1.1 lists some common salt solutions used with Axolotl's (Ambystoma mexicanum), who require harder water to maintain healthy skin. Hard water occurs in mineral and salt rich waters, resulting in a higher pH (alkaline). Other amphibians, such as most newts, should be maintained at closer to pH 7.0 (neutral pH), depending on the species. The following salt solutions should be used with caution, and only by those who have some chemistry experience in their background, as many of these solutions will need further modification in the form of dilution for any specific species. The solutions in BLACK print can be used with minor dilution, if necessary, to adjust the pH according to any given species. The solutions in GRAY print are solutions at 100% concentration, and require dilution to between 20% - 50%, depending on the species intended.

References:

Frequently Asked Questions. International Bottled Water Association. http://www.absolutelywater.com/faqs.htm (Accessed: 2001).

Indiana University Axolotl Colony. Indiana State University. http://www.indiana.edu/~axolotl/ (Accessed: 2001)