Home / Fishes / Tetras, piranhas and pacus / Aimara
No federal permit to keepAimara
Hoplerythrinus unitaeniatus
Fishes › Tetras, piranhas and pacus (Characiformes) › Erythrinidae (Wolf fish)
Hoplerythrinus unitaeniatus, the gold wolffish, aimara or yarrow, is currently treated as a single species of freshwater ray-finned fish belonging to the family Erythrinidae, the trahiras.
Care at a glance
Species-specific aquarium care
- Tank: At least 66 in long and 21 in front to back for one adult (adults commonly reach about 11.2 in / 28.5 cm).
- Water: Freshwater.
- Temperature: 73–81°F (range recorded for this species).
- pH: 5.6–7.8.
- Hardness: 0–30 dGH.
- Layout: An open-water swimmer: needs long, open swimming space with few obstacles.
- Diet: A predator: feed meaty foods sized to its mouth (frozen fish, shrimp, worms); it will eat tankmates that fit in its mouth. FishBase classes it as a carnivore.
- Availability: Mostly kept by public aquariums; private keeping is uncommon.
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, 73–81 °F, pH 5.5–7.5, 2–25 dGH.
- Behaviour: temperament predatory.
- Difficulty: Moderate (Seriously Fish rating).
Short excerpts from the species profile:
- Setup: “Ideally, keep it in a heavily planted tank with plenty of floating vegetation, which will allow it to exhibit its natural behaviour.”
- Diet: “Feeds on both insects and fish in nature.”
- Tankmates: “Despite its fearsome appearance, it can be combined with other similarly-sized species in a large tank.”
- Breeding: “It's not been bred in the hobby.”
From the Seriously Fish profile for this species, which has the full habitat, maintenance, diet, behaviour and breeding write-up 167
Wolf fish
Applies to most species in this group. Habitat: Erythrinus and Hoplerythrinus occupy shallow vegetated tributaries and floodplain waters, while giant Hoplias aimara occur in fast rivers and rapids. [fg305-rainbow, fg305-gold, fg305-wolves]. Individual species can differ, so compare with the species numbers above and the linked sources.
Housing & setup
- For one Erythrinus erythrinus, the keeper profile specifies 120 x 30 x 30 cm; this does not apply to giant wolf fish.
- For one Hoplerythrinus unitaeniatus, the profile specifies 120 x 45 x 45 cm.
- Provide abundant refuges and floating vegetation for smaller species; leave surface access for their air breathing.
- Fit a tightly secured cover because wolf fish escape and jump.
- Adult H. aimara need expert-designed housing and fast-moving, well-oxygenated water; acrylic is recommended for very large individuals.
Diet
- Earthworms.
- Prawns and mussels.
- White fish such as lancefish; routine live feeder fish risk introducing disease.
Social life
- Keep Erythrinus singly because severe conspecific fighting is documented. Sources disagree on grouping Hoplerythrinus, so solitary housing is conservative. H. aimara may attack large companions; grouping belongs to experts with extensive space.
Handling
- Keep hands away from the mouth during maintenance; wolf fish strike equipment.
- Specialist containment is needed to move adult H. aimara: bites can penetrate gloves and transport bags.
Health watch
- Bite wounds from territorial fighting.
- Jaw and tooth injuries from H. aimara striking tank walls.
- Disease or parasites introduced with live feeder fish.
Understanding the animal
About this animal
About this animal
This is a widespread fish in tropical South America, and appears to be a species complex rather than a single species.
Quoted from the Wikipedia article “Hoplerythrinus unitaeniatus” (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. Inhabits swamps and creeks with little current. |
| Water it lives in | Freshwater, 73–81 °F (23–27 °C), pH 5.6–7.8, hardness 30 dH. |
| Climate | Subtropical climate. |
| Wild diet | Hunting macrofauna (predator). |
What this means for care
- Keep water within its wild range, 73–81 °F.
Native climate (measured)
Native climate (measured)
| Warm-season highs | about 91°F (up to 95°F in the hottest sampled areas) |
| Cool-season lows | about 68°F (down to 55°F in the coldest sampled areas) |
| Average temperature | 74–81°F across sampled records |
| Relative humidity | 74–82% on average (driest month about 70%) |
| Rainfall | about 2001 mm a year |
Measured at 764 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 | Hoplerythrinus unitaeniatus, the gold wolffish, aimara or yarrow, is currently treated as a single species of freshwater ray-finned fish belonging to the family Erythrinidae, the trahiras. This is a widespread fish in tropical South America, and appears to be a species complex rather than a single 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 |
| Appearance and size | Maximum length 28.5 cm sl male/unsexed; maximum published weight 520.00 g. — FishBase |
| Biology | Obligate air-breathing; Inhabits swamps and creeks with little current, as well as in flooded savannas. Regularly goes to the surface of the water to breathe. Can survive long periods out of the water. — FishBase |
| History and naming | Hoplerythrinus unitaeniatus was first formally described as Erythrinus unitaeniatus in 1829. The type locality was the Rio São Francisco in Brazil, where the German biologist Johann Baptist von Spix collected the type, with the description being completed and published by the Swiss-American biologist Louis Agassiz. — 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.
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.
- Seriously Fish: Erythrinus erythrinus Experienced keeper or breederAdded in the 2026 source-checked care-guide review.
- Seriously Fish: Hoplerythrinus unitaeniatus Experienced keeper or breederAdded in the 2026 source-checked care-guide review.
- Oliver Lucanus, Practical Fishkeeping: Predators: Hoplias, wolves of the water Experienced keeper or breederAdded 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.
