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No federal permit to keepTwospot astyanax
Astyanax bimaculatus
Fishes › Tetras, piranhas and pacus (Characiformes) › Characidae (Tetras)
Astyanax bimaculatus, the twospot astyanax ( also called the two-spot tetra, is a species of freshwater ray-finned fish belonging to the family Acestrorhamphidae, the American characins. This fish is found in South America. It is a middlingly common…
Intro from Wikipedia (CC BY-SA 4.0)
Care at a glance
Species-specific aquarium care
- Tank: At least 36 in long and 15 in front to back for one adult (adults commonly reach about 6.9 in / 17.5 cm).
- Water: Freshwater.
- Temperature: 68–82°F (range recorded for this species).
- pH: 5.5–7.5.
- Hardness: 0–25 dGH.
- Layout: Uses both the bottom and open water: give open swimming space plus cover near the substrate.
- Diet: Eats a varied diet: mix quality prepared foods with frozen and live foods. FishBase classes it as a herbivore.
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 47 × 24 in (roughly 114 US gallons); space needed is rated “large tank”.
- Water: a fairly wide range, from slightly acidic to slightly alkaline, 68–82 °F, pH 5.5–7.5, 2–20 dGH.
- Behaviour: a shoaling fish best kept in a group of six or more; suited to a community tank.
- Difficulty: Easy (Seriously Fish rating).
Short excerpts from the species profile:
- Diet: “Unfussy and omnivorous in nature, existing chiefly on invertebrates and plant material.”
- Tankmates: “Not especially aggressive but its adult size and vigorous it's unsuitable for communities containing smaller or very sluggish species.”
- Breeding: “The most success is reported by using a 2:1 ratio of males to females.”
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
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, in rivers and streams. Uses both the bottom and open water. Inhabits large free flowing clear rivers, small streams, drainage ditches and artificial ponds and impoundments. |
| Water it lives in | Freshwater, 68–82 °F (20–28 °C), pH 5.5–7.5, hardness 25 dH. |
| Climate | Subtropical climate. |
What this means for care
- Keep water within its wild range, 68–82 °F.
Native climate (measured)
Native climate (measured)
| Warm-season highs | about 89°F (up to 91°F in the hottest sampled areas) |
| Cool-season lows | about 68°F (down to 63°F in the coldest sampled areas) |
| Average temperature | 74–80°F across sampled records |
| Relative humidity | 77–80% on average (driest month about 70%) |
| Rainfall | about 2569 mm a year |
Measured at 107 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 | Astyanax bimaculatus, the twospot astyanax ( also called the two-spot tetra, is a species of freshwater ray-finned fish belonging to the family Acestrorhamphidae, the American characins. This fish is found in South America. It is a middlingly common tetra in the aquarium industry, with hobbyist reports of its sale and presence, and it is also a well-studied member of the genus Astyanax in wild settings. Amateur aquarists report peaceful schooling behavior in captivity, though fish in wild schools may turn on one another if presented with the threat of a predatory species. — 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 |
| Wild diet | Astyanax bimaculatus is an omnivorous fish with a leaning towards plant matter. Roughly 60% of the diet is vegetal in nature, and 40% of animals; of these, dicots are the most prevalent in plants, and insects the most prevalent in animals. However, when presented with a shortage of food, A. bimaculatus is remarkably capable of changing its dietary composition. — Wikipedia (community-edited) |
| Appearance and size | Astyanax bimaculatus reaches a maximum total length of 17.5 cm, and a maximum weight of 91.6 g. The scales are large, and lack distinct radii originating from a single point in the center of each; the presence of such lines was a trait once ascribed to A. bimaculatus, but has since been recognized as a trait of congener A. abramis instead. — Wikipedia (community-edited) |
| Biology | Inhabits large free flowing clear rivers, small streams, drainage ditches and artificial ponds and impoundments. Feeds on zooplankton, detritus, higher plants and sometimes on the scales of fish. Gametogenesis takes place during the dry season in time for reproduction to begin during the rainy season. — FishBase |
| History and naming | When first described by Carl Linnaeus in 1758, A. bimaculatus was given the name Salmo bimaculatus. Throughout the 1800s, various species were named under the genus Tetragonopterus, all of which were later found to be synonymous with A. bimaculatus. In 1912, A. bimaculatus was momentarily considered a species of genus Poecilurichthys. — 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.
Maximum recorded lifespan
Longest recorded lifespan reported by each database; typical lifespans are usually shorter.
Typical adult weight
Average adult body mass in each database (FishBase gives the maximum recorded weight).
Adult length
Maximum recorded length. Measured as total length. Fish in home aquariums often stay smaller than wild records.
Water temperature
Range the species tolerates in nature; aim for the middle.
Water hardness
Minimum tank footprint
Seriously Fish recommends a tank base of at least 47 × 24 in (about 114 US gallons).
Veterinary & husbandry research
Veterinary & husbandry research
- Ovarian follicular atresia in two teleost species: a histological and ultrastructural study Miranda AC et al., Tissue & cell 1999
- Relationship between bcl-2, bax, beclin-1, and cathepsin-D proteins during postovulatory follicular regression in fish ovary Morais RD et al., Theriogenology 2016
- Bioaccumulation and Depletion of the Antibiotic Sulfadiazine (14)C in Lambari (Astyanax bimaculatus) Evangelista PA et al., Animals: an open access journal from MDPI 2023
- Gametogenesis and seminatural reproduction of the Amazon twospot astyanax Astyanax bimaculatus (Linnaeus, 1758) cultivated in an enriched environment de Sousa BL et al., Animal reproduction science 2024
Peer-reviewed papers that mention this species alongside captivity, zoos, veterinary care or aquaculture. Some cover several species or mention it only in passing, so check the abstract. See all 7 on PubMed → 170
Sources for this sheet
- AnAge: The Animal Ageing and Longevity Database (Human Ageing Genomic Resources) Peer-reviewed researchCurated, referenced longevity and life-history records for thousands of species; maximum lifespans are often from zoo animals.
- 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.
- PubMed (U.S. National Library of Medicine) Peer-reviewed researchIndex of peer-reviewed veterinary, zoo and husbandry research.
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