Cardinal tetra≈Cardinal tetra
Paracheirodon axelrodi
- Size
- 4 cm
- Temp
- 23–29°C
- Flow
- Calm
- From
- Blackwater stream
Cardinal tetra
Rio Negro and upper Orinoco, Brazil and Venezuela
- Temperament
- Peaceful
- Diet
- Omnivore
- pH
- 4.5–7
- Group
- 6+
- Typical price
- $3–7
Demo
Amazon blackwater community
River Keep demo · Large, 55–75 gal · calm, like a pond or swamp · running 1500 days · shared October 2026
Tannin-stained water, leaf litter and roots. Soft, acidic and warm enough for rams, cool enough for the tetras.
The fish
Cardinal tetra≈× 15
They school tightest when the lights first come on.
Marbled hatchetfish≈Marbled hatchetfish
Carnegiella strigata
- Size
- 3.5 cm
- Temp
- 24–28°C
- Flow
- Calm
- From
- Blackwater stream
Marbled hatchetfish
Amazon basin, Peru and Brazil
- Temperament
- Peaceful
- Diet
- Carnivore
- pH
- 5.5–7
- Group
- 6+
- Typical price
- $4–8
× 6
Keep the lid on: two jumped before we sealed the gaps.
Gold & red
Golden pencilfish≈
Golden pencilfish
Nannostomus beckfordi
- Size
- 4.5 cm
- Temp
- 24–28°C
- Flow
- Calm
- From
- Blackwater stream
Golden pencilfish
Amazon basin and the Guianas
- Temperament
- Peaceful
- Diet
- Omnivore
- pH
- 5.5–7.5
- Group
- 6+
- Typical price
- $3–6
× 6
Sterba's corydoras
Rio Guaporé, Brazil and Bolivia
- Temperament
- Peaceful
- Diet
- Omnivore
- pH
- 6–7.6
- Group
- 6+
- Typical price
- $6–12
× 8
Always busy in the sand.
German blue ram
Llanos savanna streams, Orinoco basin
- Temperament
- Peaceful
- Diet
- Omnivore
- pH
- 5–7
- Group
- 2+
- Typical price
- $12–25
× 2
The pair guards a patch of leaf litter but leaves everyone else alone.
Report
- Shared range 27–28°C
Every species is comfortable in this range.
- No hybrid risk
No two species here can cross, so any fry that turn up are pure.
- Keep a tight lid
Some of these fish jump, especially when startled.
- Stocking 57% of capacity
A rough estimate based on adult body size and tank volume.
- Tank size is a guess
Size and stocking checks use a typical tank of the size you picked. Add the real length and volume for a sharper answer.
- Some values are estimates
Care data for Cardinal tetra, German blue ram, Golden pencilfish, Marbled hatchetfish, Sterba's corydoras is estimated or taken from the genus, not yet checked against a source.