Humpbacked Glass Tetra
Roeboides descalvadensis
A highly unusual, transparent humpbacked tetra. Equipped with exterior-facing teeth, it is a specialized scale-eater (lepidophage) that will violently mutilate peaceful tankmates.
Water Temperature
22 - 28 °C
pH Value
6 - 7.5
Water type
Freshwater
Tank level
Middle
Adult size
10 cm
Minimum tank volume
>= 100 L
Minimum group
>= 6
GH
2 - 15 dGH
KH
1 - 7 dKH
TDS
40 - 295 ppm
Conductivity
63 - 461 uS/cm
Species description
Geographical Origin and Habitat: Widespread from Venezuela to the Paraguay basin. Loose schools inhabit quiet rivers, backwaters, and streams, often lurking motionless mid-water near root tangles.
Taxonomy and Morphology: Unique and sinister Characin (up to 10 cm). Features a steep 'humpbacked' profile behind the head. Its most macabre adaptation is its upper jaw: it protrudes outward, armed with hard, canine-like teeth that point FORWARD and OUTWARD from the mouth—a mechanical tool explicitly evolved to scrape scales off the flanks of live fish.
Social Behavior: Appears deceptively calm, floating at a head-down angle to mimic drifting debris or glass. It is actually a stealth ambush predator. Engages in sudden, violent sideways ramming against both conspecifics and target fish to rip off scales.
Coloration and Sexual Dimorphism: Mostly transparent/glassy with a greenish or amber tint. Distinctive black diamond or humeral spots behind the gills and at the tail base (false eyes to confuse predators). Females are slightly rounder when gravid.
Care, breeding and tankmates
Aquarium Setup: 120+ cm tank for a small group. Requires heavy wood tangles, floating plants for dim lighting, and some open swimming space. Gentle to moderate flow.
Diet and Feeding: LEPIDOPHAGE: a specialized scale-eater in the wild. Fortunately, in aquaria, they can be weaned off live scales. They become voracious meat-eaters, eagerly accepting heavy feedings of frozen bloodworms, mysis shrimp, krill, and sinking carnivore pellets.
Water Quality: Amazonian setup: clean, well-filtered. pH 5.5-7.0. Soft water, 24-28°C.
Compatibility and Cohabitation: THE REASON IT MUST BE AVOIDED IN COMMUNITY TANKS. If hungry, or sometimes out of pure instinct, they will stealth-attack peaceful, slow-moving fish (Discus, Angelfish, Geophagus). They ram their exposed teeth into the victim's side, ripping off scales and flesh. The resulting open wounds quickly become fatally infected with fungus or Columnaris. Must be kept species-only or with fast-moving tetras and heavily armored plecos.
Aquarium Breeding: Extremely rare in captivity. Open water egg-scatterers.
Risks and Diseases: 1. Mutilating and slowly killing expensive centerpiece fish (owners often mistake the sudden scale loss on their Angelfish for a disease). 2. Serious in-fighting leading to facial injuries if the tank is too small.
Geographic Origin and Distribution
Widespread from Venezuela to the Paraguay basin. Loose schools inhabit quiet rivers, backwaters, and streams, often lurking motionless mid-water near root tangles.
Origin
Amazon, Orinoco, and GuianasNorth America
Fish profile
- Temperament
- Semi-aggressive
- They have a semi-aggressive and active temperament. Their specialized feeding habits make them challenging community members. They are best suited for experienced aquarists.
- Diet
- Omnivore
- In the wild, it feeds on scales of other fish, making it a specialized lepidophage. In captivity, it can be trained to accept meaty frozen foods. Bloodworms and brine shrimp are good substitutes for its natural diet.
- Life expectancy
- 3-5 years
- The fish has a typical lifespan of 3 to 5 years in captivity under proper maintenance. Achieving this lifespan requires maintaining stable water parameters, low organic waste, and a low-stress environment. Because they are specialized feeders, providing a diet that matches their nutritional needs is critical for preventing early mortality. Regular water changes and a well-filtered system will help keep these sensitive tetras healthy and active throughout their natural life.
- Adult size
- 10 cm
- The catalog's scalar value is 10 cm. The FishBase SPECIES table (v25.04 snapshot) source reports a maximum adult measurement of 8.9 cm for this species, recorded as standard length (SL). The taxonomic record consulted is Roeboides descalvadensis (v25.04); male or unsexed record. 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.
- Sex ratio
- Solitary
- Best kept in a small group or school. A balanced ratio or more females than males helps distribute any conspecific aggression. Single individuals may become excessively timid or aggressive.
- Feeding frequency
- Twice daily
- They should be fed small amounts once or twice daily. Ensure all food is consumed to prevent water quality issues. Variety is important if they accept prepared foods.
- Bioload
- This characin has a moderate bioload typical for its size. Standard efficient filtration is generally sufficient to keep the water clean. Regular routine water changes will help keep nitrates low.
- Flow
- Stagnant
- They prefer a moderate to strong water flow simulating river currents. Good oxygenation is important for their well-being. Powerheads can be used to create appropriate flow dynamics.
- Reproduction
- Oviparous
- Breeding in captivity is rarely documented and quite difficult. They are likely egg scatterers that provide no parental care. A separate breeding setup with dim lighting would be needed.
- Compatibility & tankmates
- It can be fin-nipping and somewhat predatory towards smaller tankmates. Best kept in a species tank or with robust, similarly sized fish. Avoid housing with very small or slow-moving species.
- Tank level
- Middle
- They generally occupy the mid-water levels of the aquarium. They will actively swim and hunt in the open water. Provide some plant cover for them to retreat into.
Scientific Parameters & Models
FishBase
Window to the official scientific data of the species
Data synced on: 06/15/2026
- Trophic level
- 3.3 ± 0.46 se
- Phylogenetic uniqueness (PD50)
- 0.5
- Bayesian Length-Weight
- a = 0.01, b = 3.09
- VulnerabilityLow vulnerability (10 / 100)
Image gallery
Licensed images linked to the species or, when marked, to the closest representative taxon.
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