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Mertens' Water Monitor
Varanus mertensi
Mertens' water monitor is a highly specialized semi-aquatic Australian monitor lizard. Spending most of its life in water, it is an expert swimmer and diver, requiring large paludariums with complex filtration.
Class:Squamata
Order:Squamata
Family:Varanidae
Genus:Varanus
Species:Varanus mertensi
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Water Temperature
26 - 48 °C
Environment
Terrestrial / Semi-aquatic
Humidity
60 - 85 %
Day temperature
24 - 28 °C
Ambient temperature
28 °C
Night temperature
18 - 22 °C
Basking spot
40 - 45 °C
Adult size
54.2 cm
Minimum enclosure
>= 3,000 L
UVB
High
Species description
Geographical Origin and Habitat:
Native to northern Australia. It is a highly aquatic monitor species that inhabits tropical rivers, swamps, creeks, and billabongs.
Taxonomy and Genetics:
Belongs to the family Varanidae. Protected under Australian wildlife laws, its wild populations have suffered severe declines due to poisoning by invasive Cane Toads (Rhinella marina).
Behavior and Habits:
Diurnal and semi-aquatic. It is a powerful swimmer, spending much of its day basking on rocks or logs overhanging the water. If startled, it will immediately dive and remain submerged for long periods.
Morphology:
Reaches a total length of 100-120 cm. Features nostrils positioned on top of the snout (an aquatic adaptation) and a strongly compressed tail. Coloration is dark brown to black with numerous gold spots.
Care, breeding and tankmates
Terrarium Setup:
Requires a giant aqua-terrarium or paludarium (minimum 200x100x120h cm). The water section should make up at least 50% of the surface area and be equipped with a heavy-duty filtration system.
Lighting and Heating:
Basking area temperature of 40-45°C (104-113°F), air ambient 28-30°C (82-86°F), and water temperature 24-26°C (75-79°F). High-output UVB (10%) is mandatory.
Humidity and Hydration:
Maintain high ambient humidity (70-85%). The animal stays hydrated via the large swimming pool provided in the setup.
Feeding and Supplementation:
Diet should reflect their wild intake: fish, crayfish, crabs, mollusks, insects, and occasional rodents. Supplement with calcium and vitamins.
Compatibility:
Territorial species; adult males must not be housed together. Best kept individually unless in very large enclosures.
Health and Common Diseases:
Water sanitation is crucial. Poor water quality rapidly leads to skin rot, fungal infections, and eye issues. Ensure robust biological filtration.
Geographic Origin and Distribution
Native to northern Australia. It is a highly aquatic monitor species that inhabits tropical rivers, swamps, creeks, and billabongs.
Origin
Australia, New Guinea, and Oceania
Reptile profile
- Diet
- No verified data available
- Life expectancy
- No verified data available
- Adult size
- 54.2 cm
- Lifestyle/Microhabitat
- No verified data available
- Activity cycle
- No verified data available
- Sociality
- No verified data available
- Reproduction
- No verified data available
- Handling tolerance
- No verified data available
- Brumation
- No verified data available
- Molting
- No verified data available
The catalog's scalar value is 54.2 cm. The ReptTraits v1.2 source reports a maximum adult measurement of 54.2 cm for this species, recorded as snout–vent length (SVL). These figures are not interchangeable: the first is the profile's editorial reference, whereas the second is a published maximum under a specific measurement convention; differences among sources can reflect sex, population, life stage and measuring method.
Image gallery
Licensed images linked to the species or, when marked, to the closest representative taxon.
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