Breakdown of Female Axolotl Anatomy with Early Gender ID Potential
Whether you're trying to identify your juvenile axolotl’s gender or simply curious about what makes females tick, this blog breaks down both the visible and internal anatomy of female axolotls—with practical insights for keepers at every level.
From an external perspective, female axolotls are characterized by shorter and rounder body shapes with a small (unpronounced) cloacal bulge. Females are typically not confirmed gender until 18 months old, when the male window is closed (6-18 months).
DNA gender ID does exist, but is not widely accessible or utilized. The majority of the community relies on visual identification for gender confirmation. The cloaca can swell before a poop, and one should be mindful not to mistake a poop bump for male anatomy. Depicted below are a few images of a 3 year old confirmed female for reference.
Today we’re going to explore the internal anatomy of what makes a female axolotl a female.
Oviduct Function
The oviduct is a multifunctional organ responsible for playing roles in egg fertilization, egg formation, egg transport, supplying nutrients to embryos, and providing the eggs a supportive microenvironment.
For axolotls, fertilization is internal. The female picks up and takes in free floating spermatophores that a male axolotl has released into the water. A structure called the spermatheca (located at the exit of the oviduct) stores spermatophores (also commonly referred to as sperm cones/packets) until fertilization occurs.
In terms of egg formation, the oviduct is responsible for secreting and encasing the eggs in the jelly-like clear substance surrounding axolotl eggs. This substance helps protect the egg once it has been expelled from the ovary. The oviduct also provides a microenvironment of fluids containing substrates and co-factors that are critical for embryo development (and cleavage).
Lastly, the oviduct will transport the eggs by pushing them towards the cloaca when it is time for them to be expelled.
Ovary Function
Oogenesis or egg production is the primary function of the ovaries. Ovaries contain two cell types - oogonia (germ line stem cells) and oocytes (developing eggs) - which exist in stages within the ovaries. Oocytes cease in the diplotene stage of development. However, similarly to the oviduct, ovaries are multifaceted organs with several critical functions including yolk production, additional essential molecular production, hormone production, egg maturation, and ovarian regeneration.
There are some critical substances during oocyte differentiation that the ovaries are responsible for producing. These substances include three types of RNA (mRNA, tRNA, and rRNA), proteins, carbohydrates, fats (which make up the yolk), and melanin granules. These substances combined provide the embryo with sufficient nutrients for the post-fertilization development.
Ovaries are also the home to hormone production. One of the most critical hormones produced is progesterone, which is vital for the stimulation of oocyte development. Similar to several other vertebrate species, axolotl oocytes arrest in the diplotene stage of meiotic division (specifically the first metaphase division). Progesterone is required to break the diplotene arrest and allow for the second meiotic phase to occur. Progesterone itself is secreted from the follicle cells surrounding the oocyte.
Egg maturation occurs through cytoplasmic changes, and once the oocyte has finished meiosis through the metaphase II stage, the egg is ready for fertilization.
Axolotl females are capable of regenerating their ovaries and producing eggs even following severe injury/damage to the ovaries and their tissues. The ovaries contain oogonial stem cells (OSCs) which can be activated to repair the organ as well as produce new eggs.
Potential early gender ID for females (prior to 18 months of age)
When axolotls are juveniles, they often have an element of transparency to their skin, allowing you to make out the forms of several organ types. Of these visible organs can be the oviducts, and are often mistaken for intestines (not visible from an external view). Being a female specific organ, the appearance of oviducts in an axolotl would indicate female gender. This is not a guaranteed way to gender, but may be helpful in some cases.
Female specific “disorders”
1. Gravid
Female axolotls occasionally become gravid. This is when they produce eggs, but do not lay them. A female will not lay a clutch of eggs (typically 300-1000 per clutch) unless a male is present to deposit sperm cones. Instead of laying all of her eggs, she will reabsorb them. It is not uncommon for the female to become chunkier, have changes in eating habits, and changes in behavior.
(Photo by Ashley Hunt)
2. Reproductive disorders
There are instances of genetic reproductive disorders in females which does not allow them to reabsorb their eggs properly. This causes an accumulation of eggs for prolonged periods of time, and this accumulation can push on other organs and limit their functionality (ie pushing on the liver and resulting in edema). Additionally, the sitting eggs can generate their own internal infections that can harm the female. If you believe your female is more than gravid (concerning behavior and appetite changes, increased swelling/edema, and recurring fungal infections derived from weakened immune system) it is imperative to take them to a vet and rule out anything pathological going on.
(Photos by Brya Baverstock)
3. Mineral (calcium) deficiencies
Due to generating eggs, females require extra minerals (specifically calcium) than their male counterparts. Soft water lacks an appropriate amount of minerals, and can cause the female to become weakened over time as her mineral stores are depleted. This can present as anemia, in addition to diseases associated with weakened immune system function.
Weakened immune function related to egg holding/laying. Keeping the GH approximately 12 or above is sufficient for mineral access. A picture of anemia is attached below.
