Being a neotenic creature, the axolotl doesn’t undergo metamorphosis. Instead, it retains its juvenile features throughout its entire adult life. Such features include its characteristic external gills and the dorsal fin that extends the length of its tail. Consequently, the axolotl spends its entire life underwater, unlike other species of salamander.
So, whilst technically an amphibian, the axolotl is often mistaken for a species of fish. As a matter of fact, the axolotl is sometimes referred to as the “Mexican Walking Fish”, due to the fact that it also has 4 legs. In essence, the axolotl is a purely aquatic animal. This raises the question: “Are axolotls freshwater or saltwater animals?
Here’s what I learned:
Axolotls are native to the high-altitude lakes of Mexico City, Mexico. These lakes are endorheic, and as a result, the salinity of their water is slightly higher than that of freshwater but lower than that of seawater. This type of water is called brackish water. Axolotls have therefore evolved in, and adapted to, very slightly brackish water. Certain axolotl experts recommend preparing brackish water for pet axolotls. However, pet axolotls can also be kept in freshwater such as ordinary tap water, providing that it has the right pH, and general hardness (GH), and has been properly treated (filtered/ reverse osmosis, dechlorinated, etc.).
Continue reading below to find out more!
Table of Contents
- What Kind of Water Do Axolotls Live In?
- What Water Should I Use for An Axolotl?
- Frequently Asked Questions
What Kind of Water Do Axolotls Live In?
Axolotls are native to the high-altitude lakes of Lake Xochimilco and Lake Chalco, near Mexico City, Mexico (approx. 7200 ft or 2200 m). It’s worth noting that the former Lake Chalco was an endorheic lake – and that Lake Xochimilco still is.
An endorheic lake is a lake that doesn’t flow into an external body of water such as a river or ocean. Instead, an endorheic lake loses water through seepage or evaporation.
As a result, the salinity of endorheic lakes (concentration of salts in the water) is unique.
Salinity is measured in Total Dissolved Solids (abbreviated as TDS), expressed in mg/L (milligram per liter) or ppm (parts per million).
According to the Environmental Protection Agency of the USA, here are the salinity levels of the different types of water.
- Freshwater: < 3,000 mg/L
- Brackish water: 3,000 to 10,000 mg/L
- Saline water (saltwater): >10,000 mg/L
On the other hand, the U.S. Geological Survey (USGS) has a slightly different salinity classification.
- Freshwater: <1,000 ppm
- Slightly saline water: 1,000 ppm to 3,000 ppm
- Moderately saline water: 3,000 ppm to 10,000 ppm
- Highly saline water: 10,000 ppm to 35,000 ppm
As a reference point, seawater contains about 35,000 ppm of salt.
Finally, it’s also possible to measure the salinity of water in what’s known as specific gravity (SG). To measure SG you will need either a hydrometer or a refractometer.
Endorheic lakes tend to be more saline than other freshwater lakes, as the concentration of solutes (such as salts and minerals) left in the water is increased through evaporation.
Whilst the salinity of endorheic lake water varies considerably with precipitation levels, temperature, and other factors, it tends to be higher than the salinity of freshwater but not quite as elevated as seawater. This type of water is called brackish water.
Brackish water is also commonly found in estuaries, where fresh water and sea water meet.
What Water Should I Use for An Axolotl?
When deciding what water you should use in your axolotl tank, you have a choice between fresh water or brackish water. I strongly recommend using fresh water, as many axolotl owners say it works perfectly well for their axolotls, and it is far easier and cheaper when compared with brackish water.
Should you choose to keep your axolotl in treated tap water, check out How To Set Up An Axolotl Tank [Beginner’s Guide]. The guide explains how to prepare water for your very first axolotl tank, including cycling, testing, and conditioning.
However, axolotls have naturally evolved in mildly brackish water. And, as a result, certain axolotl experts recommend keeping them in brackish water when in captivity. Check out my dedicated guide to making brackish water if that’s what you decide to do.
Frequently Asked Questions
Should I Put Salt in My Axolotl Tank?
You should only put salt in your axolotl tank if you are planning to make brackish water for your axolotl. Moreover, you need to make sure that you are dosing the correct type of salt into the water (marine salt, not table salt), and at the right concentration. Otherwise, the salinity of your water may be too high for your axolotl and it might die.
Salt baths are used to treat certain conditions, in particular fungus growth. However, they should be prepared in a separate container or tub, not in the axolotl’s main tank.
Is Bottled Water Safe For Axolotls?
Bottled water comes in many types (still/sparkling, spring water, mineral water, filtered water, distilled water, etc.), all with unique characteristics in terms of pH, salt & mineral concentrations, etc. Therefore, it’s impossible to give a general answer.
The obvious types of bottled water to avoid would be:
- Sparkling water
- Distilled water (this water is too pure, and would draw salts and minerals out of your axolotl).
However, if your bottled water meets the criteria below, it would appear to be safe to use. This type of bottled water is generally labeled as “drinking water” or “spring water”.
- pH between 7.0 & 7.6 (the sweet spot for axolotls is actually between 7.4 & 7.6)
- Treated via filtration or reverse osmosis to remove harmful chemicals.
- Free from artificial flavors, colorants, and additives.
Finally, using bottled water for your axolotl tank is likely to become very expensive over time. Indeed, axolotls require at least a 20-gallon tank (90 liters) as well as regular water changes. That’s a lot of water!
Do Axolotls Prefer Hard or Soft Water?
Axolotls prefer slightly hard water. GH measures hard minerals in water (i.e. calcium and magnesium). Axolotls need a GH of 7 to 14 degrees of GH (dGH), equivalent to 125 to 250 ppm. Water hardness is expressed in General Hardness or GH.
The tap water in most areas is hard, which is reflected in limescale build-up in your plumbing, sinks, bathtubs, or showers (in particular on the glass), or in your kettle. Your tap water may already be hard enough for your axolotl. I found this map of water hardness, which might give you an idea of how hard your tap water is.
How Often Do Axolotls Need Water Changes?
How often you need to change the water in your tank will vary with how well your tank is cycled, how effective your filtration system is at cleaning and oxygenating the water, how many animals are in your tank, and how dirty they are. It will also depend on whether or not you regularly spot-clean your tank after feeding your axolotl and after it defecates.
However, as a general rule of thumb, you will hear experts recommend partial water changes of 20% of your water once a week and others saying that 25% every 2 weeks works well for them.