The axolotl, known for its feathery external gills, is a distinctive pet that remains fully aquatic and retains its larval characteristics throughout its life, unlike other salamanders. As their popularity grows, a common question arises regarding cohabitation: whether these delicate amphibians can share their habitat with fish. The answer is not a simple yes or no, but rather a strong caution against mixing these species due to fundamental behavioral and environmental incompatibilities.
The Incompatibility Mandate
Cohabitation between axolotls and most fish species is strongly advised against, primarily due to the severe risks posed to both creatures stemming from their natural behaviors. Axolotls are ambush predators that feed by creating a sudden vacuum to suck in prey, and they will instinctively attempt to consume anything that fits entirely or partially into their wide mouths. This opportunistic feeding behavior means that any small fish becomes a potential meal, leading to the fish’s death and a risk of impaction for the axolotl if the fish is too large to pass through the digestive system.
Axolotls also face threats from fish. The axolotl’s defining feature, its feathery external gills, are highly delicate and attractive to many fish species. Even seemingly docile fish, like Goldfish, are known to “nip” at the gills. Gill nipping causes immediate stress and physical damage to the axolotl, opening pathways for bacterial or fungal infections that can be difficult to treat in an aquatic environment.
The size difference between the two species does not guarantee safety, as a small fish can still inflict significant damage on the axolotl’s gills, while an adult axolotl can consume surprisingly large prey. Furthermore, the constant presence of a perceived threat causes chronic stress for the axolotl. Stress weakens the immune system, making the amphibian more susceptible to common diseases and shortening its lifespan.
Environmental Conflicts
Even if the behavioral risks could be mitigated, the specialized environmental needs of the axolotl fundamentally conflict with the requirements of most common aquarium fish. Axolotls thrive in cold water, with an optimal temperature range of 60–65°F (15–18°C), and they begin to experience significant stress when temperatures exceed 70°F (21°C). This narrow, cold temperature range is far too chilly for the majority of tropical fish, which require warmer temperatures to maintain a healthy metabolism.
Attempting to compromise by raising the water temperature to suit the fish would quickly compromise the health of the axolotl, leading to heat stress, a shortened lifespan, and an increased risk of fungal infections. Conversely, maintaining the cold water necessary for the axolotl would cause the fish to become lethargic, suppress their immune systems, and eventually lead to disease or death. The necessary thermal conditions for the two groups are simply mutually exclusive in a shared habitat.
Axolotls also require low-flow water conditions due to their delicate external gills and their preference for walking along the substrate rather than swimming against currents. High-powered filtration creates excessive water movement that can cause physical damage and persistent stress for the axolotl. The continuous force of the water current causes them to expend unnecessary energy and can make it difficult for them to feed or rest comfortably.
The ideal substrate also presents a conflict, as gravel is a common choice in fish tanks but poses a severe danger to axolotls. Axolotls feed by suction and frequently ingest substrate accidentally alongside their food. Any particle larger than fine sand can cause a gastrointestinal blockage, known as impaction, which is often fatal and requires expensive veterinary intervention. Axolotl habitats must therefore utilize either a bare bottom or fine sand (for adults over six inches).
Safe Tank Companions
Given the high risks associated with housing axolotls with fish, the safest approach is to keep the axolotl in a species-only tank, though a few alternatives exist that can tolerate the cold, low-flow conditions. Any potential companion must be non-aggressive, unable to fit into the axolotl’s mouth, and tolerant of the water parameters.
One of the few viable options is the inclusion of specific invertebrates:
- Large apple snails or mystery snails, though their hard shells can still pose a minor threat of impaction if the axolotl manages to bite off a large piece.
- Small, fast-moving invertebrates like ghost shrimp.
- Certain species of freshwater shrimp.
These invertebrates can survive in the cold water, though they often serve as an expensive but occasional snack for the axolotl.
It is sometimes suggested that very fast, cold-water tolerant fish, such as White Cloud Mountain Minnows or Zebra Danios, might work, but they should be viewed more as feeder fish than true companions. While their speed might allow them to evade the axolotl for a time, they will eventually be eaten, and they still carry the potential for gill-nipping behavior. Ultimately, the best environment for an axolotl is one where it is the sole inhabitant, ensuring that its highly specific needs for temperature, water movement, and safety are fully met.