Home / Fishes / Tetras, piranhas and pacus / Blackline penguinfish
No federal permit to keepBlackline penguinfish
Thayeria boehlkei
Fishes › Tetras, piranhas and pacus (Characiformes) › Characidae (Tetras)
Thayeria boehlkei, the blackline penguinfish, is a species of freshwater ray-finned fish belonging to the family Acestrorhamphidae, the American characins.
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 1.2 in / 3.15 cm).
- Water: Freshwater.
- Temperature: 72–82°F (range recorded for this species).
- pH: 6–8.
- Hardness: 5–19 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.
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 × 15 in (roughly 18 US gallons); space needed is rated “modest tank”.
- Water: 72–82 °F, 0–20 dGH.
- Behaviour: temperament peaceful; a shoaling fish best kept in a group of six or more.
- Difficulty: Easy (Seriously Fish rating).
Short excerpts from the species profile:
- Setup: “This species makes a superb addition to the heavily-planted aquarium or well-maintained community.”
- Diet: “It's a micropredator by nature, feeding on a variety of insects, worms, crustaceans and other small invertebrates in nature.”
- Tankmates: “A peaceful species that won't compete well with very boisterous or much larger tankmates.”
- Breeding: “Quite easily bred, although you'll need to set up a separate tank in which to do so if you want to raise any numbers of fry.”
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 species is endemic to the Amazon River basin and Araguaia River, in Peru and Brazil respectively. The species is popular with aquarium hobbyists, and is traded under a variety of common names including blackline penguinfish, blackline thayeria, hockey-stick tetra, penguin fish and penguin tetra.
Quoted from the Wikipedia article “Thayeria boehlkei” (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. Feeds on worms, small insects and crustaceans. In the tank, female lays a large number of eggs, which hatch in about 20 to 24 hours. |
| Water it lives in | Freshwater, 72–82 °F (22–28 °C), pH 6–8, hardness 5–19 dH. |
| Climate | Tropical climate. |
| Wild diet | Hunting macrofauna (predator). |
| Behavior to plan for | Breeding: open water/substratum egg scatterers. |
What this means for care
- Keep water within its wild range, 72–82 °F.
Native climate (measured)
Native climate (measured)
| Warm-season highs | about 93°F (up to 95°F in the hottest sampled areas) |
| Cool-season lows | about 64°F (down to 57°F in the coldest sampled areas) |
| Average temperature | 76–80°F across sampled records |
| Relative humidity | 75–80% on average (driest month about 63%) |
| Rainfall | about 1890 mm a year |
Measured at 128 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 | Thayeria boehlkei, the blackline penguinfish, is a species of freshwater ray-finned fish belonging to the family Acestrorhamphidae, the American characins. This species is endemic to the Amazon River basin and Araguaia River, in Peru and Brazil respectively. The species is popular with aquarium hobbyists, and is traded under a variety of common names including blackline penguinfish, blackline thayeria, hockey-stick tetra, penguin fish and penguin tetra. — 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 | The species feeds on worms, small insects, flake food and crustaceans. — Wikipedia (community-edited) |
| Reproduction | In captivity, this normally schooling species forms pairs that scatter their many adhesive eggs amongst plants. Clutch size is very large and may be up to 1000 eggs, the embryos of which are black in colour. The eggs hatch in about 20 hours and are free-swimming after four days. — Wikipedia (community-edited) |
| Biology | Feeds on worms, small insects and crustaceans. In the tank, female lays a large number of eggs, which hatch in about 20 to 24 hours. Maximum length reported to reach 6 cm TL. — FishBase |
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
Minimum tank footprint
Seriously Fish recommends a tank base of at least 24 × 15 in (about 18 US gallons).
Veterinary & husbandry research
Veterinary & husbandry research
- Complete mitochondrial genome of the penguin tetra, Thayeria boehlkei Xiao GB et al., Mitochondrial DNA. Part A, DNA mapping, sequencing, and analysis 2016
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. 170
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.
- PubMed (U.S. National Library of Medicine) Peer-reviewed researchIndex of peer-reviewed veterinary, zoo and husbandry research.
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