Fish comparison
Cardinal Tetra vs Red-Tailed Black Shark
How the Cardinal Tetra and Red-Tailed Black Shark compare on care, size, water and temperament, and which fish suits your tank.
By Mike ElmiraUpdated
TL;DR, Cardinal Tetra vs Red-Tailed Black Shark
The Cardinal Tetra and the Red-Tailed Black Shark come up together a lot when people are choosing a fish, and they are close enough to weigh side by side. Both are happy somewhere around 23 to 26 °C and pH 6.5 to 6.5, so a single tank can suit either one. Neither is harder than the other to keep, so the choice comes down to look and stocking rather than skill. If tank space is tight, the Cardinal Tetra needs less room to feel settled; give the Red-Tailed Black Shark the nod when you have the litres to spare.
Group compatibility overview
Good fit
Workable as-is, only minor advisories to plan around.
1 warning · 2 notes
Temperature
- Cardinal Tetra23–27 °C
- Red-Tailed Black Shark22–26 °C
pH
- Cardinal Tetra4.5–6.5
- Red-Tailed Black Shark6.5–7.5
Hardness
- Cardinal Tetra1–6 dGH
- Red-Tailed Black Shark5–15 dGH
What to plan for
- Narrow pH overlapTarget pH is 6.5–6.5. Test weekly; use buffered substrate or remineraliser to keep it stable.
- Cardinal Tetra schools, stock at least 8You've planned for 1 cardinal tetra. Cardinal Tetra need a group of at least 8 to feel safe and shoal naturally, below that they're stressed and lose colour. Dial up the count, or remove the species.
- 67% of your fish swim in the midHeavy concentration in a single zone. Spreading stocking across all three levels makes the tank read fuller for the same bioload.
Full attributes
Every parameter, side by side| Parameter |  FishCardinal TetraParacheirodon axelrodi |  FishRed-Tailed Black SharkEpalzeorhynchos bicolor |
|---|---|---|
| Category | Fish | Fish |
| Origin | Upper Orinoco and Rio Negro basins | Thailand (Chao Phraya basin), critically endangered in the wild |
| Family | Characidae | Cyprinidae |
| Temperature | 23–27 °C | 22–26 °C |
| pH | 4.5–6.5 | 6.5–7.5 |
| Hardness (dGH) | 1–6 | 5–15 |
| Flow rate | Low | Medium |
| Min tank | 75 L | 200 L |
| Adult size | 4–5 cm | 12–15 cm |
| Difficulty | 3 / 5 | 3 / 5 |
| Lifespan | 4–6 yrs | 6–8 yrs |
| Diet | Omnivore | Omnivore (heavy on algae and plant matter) |
| Water column | Mid | Bottom to Mid |
| Schooling | Yes | No |
| Plant safe | Yes | Yes (mostly) |
| Shrimp safe | Mostly (may eat shrimplets) | No (will hunt) |
Frequently asked questions
Direct answers to the questions search engines and AI assistants surface most often about this species.
Can you keep Cardinal Tetra and Red-Tailed Black Shark together?
Yes. Their temperature and pH ranges overlap around 23 to 26 °C and pH 6.5 to 6.5, so one set of water conditions keeps both comfortable. Match group sizes and cover the usual planted-tank basics and they share a tank fine.
Which is easier to keep, the Cardinal Tetra or the Red-Tailed Black Shark?
They sit at the same care level, both middle-of-the-road, so neither is the obvious beginner pick. The decision is really about the look you're after.
Do Cardinal Tetra and Red-Tailed Black Shark need the same water?
Close to it. Aim for 23 to 26 °C and pH 6.5 to 6.5 and you're in the shared sweet spot for both. Full ranges are in the table above.
What's the main difference between the Cardinal Tetra and the Red-Tailed Black Shark?
Temperament is the big one. The Cardinal Tetra is peaceful and the Red-Tailed Black Shark is territorial when breeding, which changes who you can house them with.