Home / Fishes / Tetras, piranhas and pacus / Ruby tetra
No federal permit to keepRuby tetra
Axelrodia riesei
Fishes › Tetras, piranhas and pacus (Characiformes) › Characidae (Tetras)
The ruby tetra (Axelrodia riesei) is a species of freshwater ray-finned fish belonging to the family Acestrorhamphidae, the American tetras.
Care at a glance
Species-specific aquarium care
- Tank: At least 24 in long and 12 in front to back for one adult (adults commonly reach about 0.8 in / 2.14 cm).
- Water: Freshwater.
- Temperature: 68–79°F (range recorded for this species).
- Hardness: 0–8 dGH.
- Layout: Uses both the bottom and open water: give open swimming space plus cover near the substrate.
Calculated from this species' own FishBase record: tank size from its typical adult length and swimming zone, water values from its recorded ranges. The group guide below fills in general care.
Care guide
Species care notes
- Tank: a base of at least 24 × 12 in (roughly 14 US gallons); space needed is rated “modest tank”.
- Water: soft, acidic water, 68–82 °F, pH 4–6.5, 1–5 dGH.
- Behaviour: temperament peaceful; a shoaling fish best kept in a group of six or more; not a community fish.
- Difficulty: Moderate (Seriously Fish rating).
Short excerpts from the species profile:
- Setup: “Best-maintained in a well-structured set-up, ideally comprising a sandy substrate plus some driftwood roots and branches.”
- Diet: “Probably a micropredator feeding on tiny invertebrates and other zooplankton in nature.”
- Tankmates: “Peaceful with other species but does not make an ideal community fish due to its small size and somewhat specialised requirements Ideally it should be maintained alone or at most with diminutive, non-aggressive characids and smaller callichthyid or loricariid…”
- Breeding: “Has been achieved and in a properly-structured, mature aquarium it's possible that small numbers of fry may start to appear without intervention.”
From the Seriously Fish profile for this species, which has the full habitat, maintenance, diet, behaviour and breeding write-up 167
Tetras
Applies to most species in this group. Habitat: The covered characids include South American river and tributary fishes, from vegetation-shaded bloodfin habitats to sandy flowing rivers occupied by Exodon. [fg156-bloodfin, fg156-exodon]. Individual species can differ, so compare with the species numbers above and the linked sources.
Housing & setup
- For glass bloodfins, use at least 60 × 38 × 30 cm (24 × 15 × 12 in), retaining open upper-water swimming space.
- Provide planted margins and floating vegetation for bloodfins; fit a tight lid for Aphyocharax anisitsi.
- For bucktooth tetras use at least 120 × 45 × 45 cm (48 × 18 × 18 in), efficient filtration and planted refuges from bullying.
- For glass bloodfins maintain pH 6.0–7.5; for Exodon, pH 5.5–7.5.
Climate & lighting
| Water | 73.4–80.6°F |
Diet
- Small dried foods for glass and ordinary bloodfins.
- Daphnia, Cyclops and bloodworms for glass bloodfins.
- For Exodon, chopped prawns, mussels, earthworms and fish rather than live feeder fish.
Social life
- Glass bloodfins need 6–8 or more; ordinary bloodfins at least six. Exodon requires a species aquarium and at least 12 introduced together; small groups can kill one another.
Health watch
- Freshwater ich (white spot disease), a general aquarium risk.
- Bacterial infections associated with stress and poor water quality.
- Fin and scale damage from aggression, especially Exodon.
Understanding the animal
About this animal
About this animal
This fish is found in northern South America.
Quoted from the Wikipedia article “Ruby tetra” (CC BY-SA 4.0) 174
In the wild
In the wild
From this species’ own FishBase record (habitat, bottom type, water and breeding data), not its family. Good care copies these conditions.1
| Where it lives | Lives in freshwater. Uses both the bottom and open water. Strongly red in nature, but gets pale in captivity. Maximum length reported to reach 4 cm TL. |
| Water it lives in | Freshwater, 68–79 °F (20–26 °C), pH 7, hardness 8 dH. |
| Climate | Tropical climate. |
What this means for care
- Keep water within its wild range, 68–79 °F.
Native climate (measured)
Native climate (measured)
| Warm-season highs | about 93°F (up to 96°F in the hottest sampled areas) |
| Cool-season lows | about 71°F (down to 69°F in the coldest sampled areas) |
| Average temperature | 79–82°F across sampled records |
| Relative humidity | 75–84% on average (driest month about 65%) |
| Rainfall | about 2540 mm a year |
Measured at 33 wild occurrence records sampled against WorldClim 2.1 climate data (1970–2000 averages). Air conditions in the range are ecological context, not enclosure settings: microhabitats such as burrows, leaf litter or basking rocks can be cooler, warmer or more humid.
From the sources
From the sources
Quoted from the matching sections of reputable sources for this exact species. Specialist databases are used first; Wikipedia (community-edited, CC BY-SA 4.0) only fills gaps. Other sources are short credited quotes.
| Overview | The ruby tetra (Axelrodia riesei) is a species of freshwater ray-finned fish belonging to the family Acestrorhamphidae, the American tetras. This fish is found in northern South America. — Wikipedia (community-edited) |
| Where it lives | Home ranges Population dynamics Growth parameters Max. ages / sizes Length-weight rel. Length-frequencies Mass conversion Recruitment Abundance Life cycle Reproduction Maturity Maturity/Gills rel. — FishBase |
| Appearance and size | The ruby tetra is a small fish with a maximum standard length of 2.5 cm. The dominant colour of this species is ruby red, but this fades in captivity. This species can be told apart from A. stigmatias by having 14 or 15 rays in the anal fin, having between 7 and 10 premaxillary teeth and 4 or 5 maxillary teeth, and its standard length being over 3 times the depth of the body. — Wikipedia (community-edited) |
| Biology | Strongly red in nature, but gets pale in captivity. Maximum length reported to reach 4 cm TL. — FishBase |
| History and naming | The ruby tetra was first formally described in 1965 by the French ichthyologist Jacques Géry, with its type locality given as the Upper Río Meta basin, east of Villavicencio in Colombia. Axelrodia was first proposed as a monospecific genus in 1965 by Géry, with its only species being Axelrodia fowleri, and this taxon also being designated as the type species by Géry. — Wikipedia (community-edited) |
Data and studies
The numbers
The numbers
Each bar is what one source reports. Where several sources weigh in, the dashed gold band marks their average.
Adult length
Maximum recorded length. Measured as standard length (snout to the base of the tail, not counting the tail fin). Fish in home aquariums often stay smaller than wild records.
Water temperature
Range the species tolerates in nature; aim for the middle.
pH
Water hardness
Minimum tank footprint
Seriously Fish recommends a tank base of at least 24 × 12 in (about 14 US gallons).
Sources for this sheet
- FishBase (Froese & Pauly, eds.), version 24.07 Peer-reviewed researchThe global scientific database on fishes, maintained by a consortium of research institutions; every value is referenced.
- Seriously Fish species profiles Experienced keeper or breederLong-running aquarium reference written and peer-checked by experienced fishkeepers and ichthyologists; each profile covers habitat, tank size, water, diet, behaviour and breeding.
- Seriously Fish: Prionobrama filigera Experienced keeper or breederAdded in the 2026 source-checked care-guide review.
- Seriously Fish: Exodon paradoxus Experienced keeper or breederAdded in the 2026 source-checked care-guide review.
- Seriously Fish: Aphyocharax anisitsi Experienced keeper or breederAdded in the 2026 source-checked care-guide review.
- Merck Veterinary Manual: Disorders and Diseases of Fish Zoo, university or veterinaryAdded in the 2026 source-checked care-guide review.
- Wikipedia (species article) Community referenceFree encyclopedia; useful overviews with their own citations. Intro text is quoted under CC BY-SA 4.0.
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