My Axolotl's Gills Look Wrong

External gills are the single best at-a-glance health indicator an axolotl keeper has, precisely because they sit outside the body and respond visibly, often within hours, to changes in the water the animal is sitting in. Before assuming disease, the water itself is always the first thing to test — not the animal.

Start with a liquid-reagent test kit (test strips are considerably less reliable for ammonia specifically) and check ammonia, nitrite, nitrate, pH, and temperature. In a newly set-up tank, or one that's had a recent large water change, filter media rinse, or filter replacement, ammonia and nitrite are the prime suspects — a fully cycled tank should read essentially 0 ppm ammonia and 0 ppm nitrite. Axolotls are considerably more sensitive to ammonia than most fish kept at comparable stocking density, so 'the fish were fine' is not a reassuring data point if fish shared the same water.

Temperature comes next: axolotls should be kept at 60-68°F (16-20°C), with performance and immune function declining as temperatures climb toward 74°F (23°C) and becoming dangerous above that. A room that's warmed up for summer, a tank near a sunny window, or a heater left on from a mixed-species setup are the most common causes of an axolotl tank running warmer than intended. Gills clamping flat and going pale alongside reduced appetite and lethargy, in a tank that's crept above the target range, points squarely at heat stress rather than infection — and the fix (a chiller, ice packs in a sealed bag rotated through the water, moving the tank to a cooler room, or increasing surface agitation) is different from a fungal or bacterial treatment protocol.

If water parameters and temperature check out normal, look closely at the gill tissue itself under good light. Symmetrical, generalized shrinkage with no fuzz, discoloration, or fraying, in an axolotl that is still eating and moving normally, is most likely either a slow-building water-quality issue not yet caught by a single test (do several tests over a couple of days) or the normal adaptive response to strong filter flow or high dissolved oxygen — some keepers see gills shrink somewhat after upgrading to a stronger filter, and it isn't necessarily a problem if nothing else about the animal has changed.

A white or grey cotton-like coating on the gill filaments is the clearest sign to treat as a genuine infection rather than a water-quality reaction. Saprolegnia and related water molds are present in virtually all aquarium water and take hold on tissue that's already stressed or injured, which is why the underlying water-quality or injury issue needs addressing alongside any antifungal treatment — treating the fungus without fixing what let it take hold invites a relapse. Because over-the-counter fish antifungal medications vary enormously in axolotl safety (many contain malachite green or formalin, both of which are dangerous to amphibians at fish-labeled doses), this is a case to get exotic-vet or, at minimum, experienced-axolotl-community guidance on treatment rather than reaching for the first fish-tank product on a pet-store shelf.

Uneven, frayed damage concentrated on one side or in patches, with clean rather than fuzzy edges, points toward physical trauma — most often from a tankmate. Axolotls are frequently sold as needing to be housed alone specifically because they will bite at each other's gills and limbs, especially around feeding time or in a tank too small to let a submissive animal retreat; fish sharing the tank, even 'safe' species like small livebearers, will sometimes nip at the trailing gill filaments as well. The management here is separation, not medication, and gills that were bitten rather than infected typically regrow over subsequent weeks as the axolotl continues its normal regeneration and molting-like skin turnover, provided water quality stays clean while they heal.

The signs that turn a gill concern into a same-day or next-day exotic vet visit rather than a home water-quality fix are: gills that are actively fuzzy and spreading rather than static, an axolotl that has also stopped eating and become lethargic or is floating/sinking abnormally (suggesting the gill issue is one symptom of a broader systemic problem), visible open wounds beyond the gills themselves, or gill clamping that persists for more than 48-72 hours after ammonia, nitrite, and temperature have all been corrected to normal range. Exotic-vet access for aquatic amphibians specifically is limited even by exotics-vet standards — many general exotics practices see reptiles and birds routinely but rarely axolotls — so it's worth identifying a vet comfortable with amphibians (sometimes an aquatics-focused exotics vet, or one who also treats ornamental koi/fish) before an emergency happens, rather than during one.

Cycle the tank fully before adding an axolotl, and re-test ammonia and nitrite for several days after any filter media change, large water change, or new decor addition — these are the single most common triggers for a sudden gill-appearance change in an otherwise well-established tank, and a five-minute liquid test kit check is far cheaper than treating a fungal infection that took hold because of a missed ammonia spike.

Keep the tank meaningfully within the 60-68°F range year-round, which for most households means planning for summer heat before it arrives — a small aquarium chiller, a tank sited away from direct sun and heating vents, or simply monitoring a thermometer daily through warm months, rather than discovering a problem only once gills have already clamped and appetite has dropped.

House axolotls alone or with only well-matched, size-appropriate axolotl tankmates, never with fin-nipping fish species, and provide enough floor space and hides that a subordinate or smaller axolotl in a multi-axolotl setup can retreat out of biting range during feeding — gill trauma from tankmates is avoided almost entirely through sensible stocking choices made at setup time.

Maintain a consistent maintenance schedule (partial water changes on a fixed cadence rather than reactive, infrequent large ones) so ammonia and nitrate stay low and stable rather than swinging — stable water chemistry is protective against both the direct gill stress of ammonia exposure and the secondary fungal infections that follow once tissue is already compromised.