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No federal permit to keepThreadfin acara
Acarichthys heckelii
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The threadfin acara (Acarichthys heckelii), also known as Heckel's thread-finned acara, is a South American species of cichlid fish.
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 7.7 in / 19.5 cm).
- Water: Freshwater.
- Temperature: 73–79°F (range recorded for this species).
- Layout: Uses both the bottom and open water: give open swimming space plus cover near the substrate.
- Diet: FishBase classes it as a omnivore.
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
- Water: a fairly wide range, from slightly acidic to slightly alkaline, 75–86 °F, pH 6–8, 1–12 dGH.
- Difficulty: Moderate (Seriously Fish rating).
Short excerpts from the species profile:
- Setup: “A sandy substrate is recommended although gravel can be used if you wish, the main disadvantage being that this species is an incessant digger so if the latter is used any aquascaping will quickly be rearranged.”
- Diet: “This species does not sift sand like some related species, rather spending much its time in midwater.”
- Tankmates: “Relatively peaceful in the main and will not prey on anything larger than a couple of centimetres in size.”
- Breeding: “This species requires 2-3 years to reach sexual maturity and in nature exhibits an intriguing spawning strategy whereby females compete for territories and excavate complex, burrow-like substructures from the substrate.”
From the Seriously Fish profile for this species, which has the full habitat, maintenance, diet, behaviour and breeding write-up 167
Oscars, peacock bass, pike cichlids and eartheaters
Applies to most species in this group. Habitat: Large South American rivers. Individual species can differ, so compare with the species numbers above and the linked sources.
Housing & setup
- For one adult Astronotus ocellatus, plan at least a 150 × 60 cm base according to Seriously Fish; pairs and groups need more space. Use separate adult plans for Cichla and each eartheater species.
- Soft sand for eartheaters (Geophagus, Satanoperca), which sift substrate through their gills.
Climate & lighting
Starting point only: The blanket warm-water interval excludes the subtropical seasonal requirements of G. balzanii; use overrides. Check the species-specific values for this animal where shown.
| Water | 77–84°F |
Diet
- Astronotus ocellatus is an omnivore with a preference for animal foods; offer quality pellets and varied suitable foods rather than feeder-fish dependence. Cichla and substrate-sifting eartheaters require separate feeding plans.
Health watch
- Hole-in-the-head disease and lateral line erosion in poor water; eartheaters suffer on sharp gravel.
Understanding the animal
About this animal
About this animal
It is the only member of the genus Acarichthys and is native to rivers in the Amazon and Essequibo basins in tropical South America, and has become established in southeastern Asia. It is sometimes found in the aquarium trade.
Quoted from the Wikipedia article “Threadfin acara” (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, in rivers and streams. Uses both the bottom and open water. |
| Water it lives in | Freshwater, 73–79 °F (23–26 °C), hardness 18 dH. |
| Climate | Tropical climate. |
| Behavior to plan for | Breeding: nesters. |
What this means for care
- Keep water within its wild range, 73–79 °F.
Native climate (measured)
Native climate (measured)
| Warm-season highs | about 90°F (up to 91°F in the hottest sampled areas) |
| Cool-season lows | about 71°F (down to 68°F in the coldest sampled areas) |
| Average temperature | 79–80°F across sampled records |
| Relative humidity | 82–85% on average (driest month about 79%) |
| Rainfall | about 2182 mm a year |
Measured at 83 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 threadfin acara (Acarichthys heckelii), also known as Heckel's thread-finned acara, is a South American species of cichlid fish. It is the only member of the genus Acarichthys and is native to rivers in the Amazon and Essequibo basins in tropical South America, and has become established in southeastern Asia. It is sometimes found in the aquarium trade. — 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 | This is a laterally-compressed, deep-bodied fish with a brownish-silver upper body, silvery flanks and a pale belly. There is a vertical black streak below the eye, a black blotch on the front few rays of the dorsal fin and a small black spot on the flanks below the centre of the dorsal fin. — Wikipedia (community-edited) |
| History and naming | The threadfin acara was first described in 1848 by the German zoologists J. P. Müller and Troschel as Acara heckelii, and in 1912 was placed by C. H. Eigenmann in the monotypic genus Acarichthys. Its common name is the "threadfin acara", referring to the elongated, free rays at the posterior end of the dorsal fin. — 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.
Typical adult weight
Average adult body mass in each database (FishBase gives the maximum recorded weight).
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
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.
- Merck Veterinary Manual: Management of aquarium fish Zoo, university or veterinaryThe Merck Veterinary Manual: a standard veterinary reference written and reviewed by veterinary specialists.
- Merck Veterinary Manual: Types and features of aquatic systems Zoo, university or veterinaryThe Merck Veterinary Manual: a standard veterinary reference written and reviewed by veterinary specialists.
- Seriously Fish: Gymnogeophagus balzanii Experienced keeper or breederAdded in the 2026 source-checked care-guide review.
- Seriously Fish — Astronotus ocellatus 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.
- iNaturalist (captive observations) Community referenceCommunity observation platform run by the California Academy of Sciences and National Geographic; observations marked captive show animals living in homes, zoos and aquariums.
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