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Axolotl sizes: what is the difference between a mini, dwarf and short toes axolotl?

Dwarfism

MissPiggy, a four-month-old dwarf axolotl. Photo: Briitney Alyssah Darlene Long
This picture of Tadpole, a dwarf axolotl, shows the added strain that the condition puts on female axolotls’ bodies when gravid. Photo: Patricia’s Gill Babies

Dwarfism is a genetic condition which causes a foreshortening of the chest area and a smaller than usual adult size. Limbs may also appear shorter than usual, although the axolotl’s fingers and toes keep a normal appearance. Dwarfism can lead to health issues and shortened lifespans, particularly in females, due to the large number of eggs they carry. Dwarf axolotls should never be allowed to breed, and may need to be housed separately to avoid getting picked on by larger adults.

‘Mini’ features

Ravyn the mini axolotl only reached an adult size of six inches. Photo: Patricia’s Gill Babies

A mini axolotl is one whose growth stops before reaching adult size, which can be the result of genetic issues (often due to inbreeding) or stunting due to poor husbandry. Minis may be normally proportioned, or have a somewhat smaller than average tail, with normal chest and limbs. Just like dwarves, minis may require separate housing, and it is preferable not to breed them.

Short toes syndrome

Axolotl suffering from short toes syndrome. Unfortunately, some unscrupulous breeders take advantage of this painful and deadly condition by marketing the afflicted animals as “dwarf axolotls”. Buyers beware! Photo: Amanda Gomes

Axolotls with short toes syndrome look similar to dwarves, but they have short fingers and toes that give their hands and feet a padded appearance. Over time, they develop a pudgy appearance due to oedema, an accumulation of interstitial fluid within the body tissues, which causes bloating of the entire body (pictured above). Short toes syndrome is a very serious and irreversible condition which invariably leads to painful oedema, hemorrhages and organ failure. To prevent unnecessary suffering, axolotls affected by this condition should be euthanized as soon as the condition is detected.

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Axolotl Diseases

This is a quick reference list of common health issues, as well as axolotl-safe treatments. I will add to this article little by little. If you’d like me to talk about one illness in particular, please email me.

Ammonia poisoning

Deformation of the caudal fin and bleeding due to ammonia poisoning.

Early symptoms:

  • Lack of appetite
  • Curling, atrophy of gill filaments
  • Irritated skin (some redness visible on axolotls with pale skin)
  • Veins becoming more visible (also on axolotls with pale skin)

Advanced symptoms:

  • Whitening, curling, atrophy of gill stalk tips
  • Prounounced red patches on the skin (visible on axolotls with pale skin)
  • Loss of gill filaments
  • Deformation of the caudal fin
  • Erosion of the tail tip and fingertips
  • Bleeding
  • Death

How to diagnose:

In the presence of some or all of the above symptoms, test ammonia levels. If any ammonia is detected, the animal is almost certainly suffering from ammonia poisoning.

Causes:

Ammonia poisoning is either due to new tank syndrome or improper husbandry (infrequent water changes, overcrowding, overfeeding, or using inadequate filtration).

Treatment:

If the cause is new tank syndrome, follow the treatment instructions listed below. Otherwise, you will need to find the cause of the problem and fix it. Daily 50% water changes and the addition of conditioner every 24 hours will keep your animals safe until the issue is resolved. Keep testing the water for ammonia every 24 hours until no more ammonia is detected. To prevent the situation from reoccuring in the future, I highly recommend testing ammonia once a week.

New tank syndrome

Early symptoms:

  • Gradual loss of vitality, typically within the first month following the introduction of the axolotl to a new aquarium
  • Red patches on the skin (visible on axolotls with pale skin)
  • Curling, atrophy of gill filaments
  • Lack of appetite or inability to chew or swallow food
  • Change in gill color (paler or more brownish)

Advanced symptoms:

  • Whitening, curling, atrophy of gill stalk tips
  • Loss of gill filaments
  • Erosion and/or deformation of the caudal fin
  • Bleeding
  • Death

How to diagnose:

In the presence of some or all of the above symptoms, test ammonia, nitrite and nitrate levels. You can assume that the animal is suffering from new tank syndrome ammonia and/or nitrites are detected and one or more of the following statements are true:

  • Nitrates are absent or very low (~10 ppm or less)
  • The animal has been living in the aquarium for less than two months
  • The filter is brand new, or the filter media has been completely replaced recently
  • The filter stopped running (e.g. during a power outage) for three hours or more
  • You have recently treated the tank with an antibiotic
  • You have been refilling your aquarium with tap water, without adding conditioner

If ammonia and/or nitrites are present but nitrates are also high (>40 ppm) and none of the other conditions apply, a more likely diagnosis is ammonia poisoning and/or nitrite poisoning due to improper husbandry (infrequent water changes, overcrowding, overfeeding, or using inadequate filtration).

Causes:

Uncycled aquarium (lack of nitrifying bacteria in the filter) leading to ammonia poisoning and/or nitrite poisoning.

Treatment:

Daily water changes and addition of conditioner as needed until the aquarium is properly cycled. The addition of seeded filter media or a bacterial additive is strongly recommended.

Nitrite poisoning

Early symptoms:

  • Very pale gills
  • Frequent breathing at the water surface
  • Crowding near the water inlet or air stone

Advanced symptoms:

  • Gills turning brown
  • Uncontrolled floating
  • Lethargy
  • Lack of interest in food
  • Gill damage, gill loss and/or saprolegniosis
  • Eventual death

Diagnosis:

In the presence of some or all of the above symptoms, test nitrite levels. If any are detectable, you can assume that the animal is suffering from nitrite poisoning.

Causes:

Frequently occurs as part of new tank syndrome or as the result of a cycle crash (e.g. after a power failure). May also be due to overstocking, the presence of something rotting in the tank, or infrequent water changes.

Treatment:

Daily water changes and addition of conditioner as needed until the aquarium is properly cycled. The addition of seeded filter media or a bacterial additive is strongly recommended. Make sure the tank isn’t overstocked and that partial water changes are conducted at least once a week.

Saprolegniosis (winter fungus)

Early signs of saprolegnia.

Early symptoms:

  • Raised white or grey lesions that have a soft appearance, like cotton wool. Typically start as small circles on the axolotl’s head or gills, then grow larger and merge as the disease progresses.

Advanced symptoms:

  • A fuzzy growth, reminiscent of a dandelion puff, typically on the axolotl’s gills — may appear white, grey or tan to brown as debris accumulate
  • Partial loss of gill stalks
  • Death, if internal organs are affected

Causes:

Compromised immune system due to stress, reducing the animal’s natural resistance to saprolegnia (a fungus whose spores are naturally present in virtually all water sources). May appear as a secondary infection if the axolotl is already battling another illness.

Diagnosis: 

The visual cues are usually pretty obvious. In the presence of some or all of the above symptoms, your veterinarian may conduct a skin scraping to identify Saprolegnia’s hyphae (a root-like structure) under a microscope.

Treatment:

Eliminate potential stress causes such as improper housing conditions, poor water quality (especially in an uncycled aquarium), high temperatures, aggressive tankmates or strong water flow. If the axolotl is on the verge of laying eggs or recovering after egg-laying, it may help to isolate her and lower the temperature slightly to help her recuperate. The same applies to an axolotl who is in the process of regrowing a limb. In advanced cases, salt baths are recommended.

Short Toes Syndrome

Axolotl suffering from short toes syndrome. Unfortunately, some unscrupulous breeders take advantage of this painful and deadly condition by marketing the afflicted animals as “dwarf axolotls”. Buyers beware! Photo: Amanda Gomes

Early symptoms:

  • Unusually short limbs and toes
  • Inability to regenerate missing limbs
  • Shortened/missing bones and bone joints

Advanced symptoms:

  • Signs of pain and distress (forward gills, mouth hanging open, arched spine, lack of interest in food, lack of movement)
  • Internal bleeding
  • Skin blisters
  • Hemorrhages
  • Extreme swelling and bloating

Causes:

Short toes is caused by a genetic mutation, which results in skeletal, renal and urogenital malformations. The afflicted animals have shortened lifespans, eventually suffering from painful edema and kidney failure.

Diagnosis:

The shortened toes are a sufficient cue.

Treatment:

Unfortunately, not much can be done to alleviate the issues caused by the mutation. Studies suggest Holtfreter’s solution may help for a time, but it may be kinder to euthanize the animal to spare it further suffering. Alternatively, you may consider donating your axolotl to a university, as short toes axolotls are important to limb regeneration research.