Why Knowing Your Axolotl’s Sex Matters

Knowing whether an axolotl is male or female is not just trivia, it affects how you care for them. Important reasons include:

• Preventing unwanted breeding: If you own more than one axolotl, being sure of each animal’s sex can avert accidental breeding. Axolotls lay hundreds of eggs when a male and female are together, often without obvious warning. House males and females in separate tanks if you do not intend to breed them​. Even aquarium dividers may be unreliable because male axolotls release packets of sperm (spermatophores) into the water​. These can drift through mesh or open water and be used to fertilize eggs, so the only surefire way to stop breeding is to keep the sexes fully apart. By identifying sex early, owners can avoid the surprise of eggs and the complications euthanizing or of raising axolotl larvae.

• Breeding Harms Females: Laying eggs is an extremely taxing process for female axolotls, even if the eggs are later removed or euthanized. Producing hundreds of eggs requires significant energy and nutrient reserves, putting immense strain on the female’s body. Repeated or unnecessary breeding can lead to exhaustion, malnutrition, and even organ damage over time. Even a single, unplanned spawning event forces the female to deplete resources that could otherwise support her long-term health. For this reason, it is far better to prevent mating altogether rather than assume it is harmless to simply dispose of unwanted eggs. Protecting females from the physical demands of reproduction helps ensure they stay strong, healthy, and live their full natural lifespan.

Physical Differences Between Males and Females

Cloacal region (vent). The single most reliable clue is the appearance of the cloaca (the common exit for the digestive and reproductive tracts) near the base of the tail. In males, this area develops a noticeable swelling or glandular bulge​. This “cloacal bulge” (sometimes called enlarged cloacal glands) is absent in females. Mature males also have a longer and more tapered vent area, whereas a female’s cloaca remains flat against her body profile​. In practice, looking from above or from the side, a male’s vent will protrude slightly and may show a whitish tip, while a female’s vent stays flush and often V-shaped. These glands are much more pronounced after sexual maturity (around 12–18 months old)​, so careful observation after one year is key.

Overall body shape. Beyond the cloaca, the general silhouette differs by sex.  Females tend to have rounder, “pear-shaped” bodies with a wider midsection and abdomen​. This is because mature females carry hundreds of developing eggs, which makes their bodies appear plump or distended​​. By contrast, males are usually slimmer and more elongated. From a top view, a male’s body looks lean and rectangular (or even slightly curved in), whereas a female’s body widens noticeably behind the shoulders​. (Owners often describe a gravid female as looking visibly “fatter” than a male of the same length.) Both sexes can reach similar lengths, but the female’s girth is the giveaway. Over time, even non-spawning females maintain a fuller body shape than males of comparable age​.

Other skin features. There are a few additional cues, though they are subtler. Male axolotls develop small cloacal papillae – tiny fleshy bumps or protrusions near the vent – which are usually longer and more pronounced than any papillae a female has​. These are often whitish or pinkish and can be seen upon very close inspection of the cloacal opening. During breeding season, breeding tubercles (small white spines) can appear on adult males’ heads, limbs, and tails​; females do not grow these bumps. (However, tubercles are only present seasonally, so they are not a year-round sexing method.) In terms of coloration and gill appearance, there is no reliable difference: males and females come in all the same color morphs, and gill size or color does not indicate sex.