Can Cardinal Tetra and Green Spotted Puffer (Brackish) Live Together?

Cardinal Tetra is a peaceful species (1/10), while Green Spotted Puffer (Brackish) is highly aggressive (9/10). This notable difference means Green Spotted Puffer (Brackish) may occasionally assert dominance over Cardinal Tetra.

Large aggression gap (8 points) between Cardinal Tetra and Green Spotted Puffer (Brackish) increases stress risk for the more peaceful fish.

Cardinal Tetra and Green Spotted Puffer (Brackish) both frequent the Middle (Open Water) region of the setup. This overlap can increase competition for space, so providing ample room and cover is important to keep both species comfortable.

Additional behavioural considerations to keep in mind: Aggressive fish may bully and stress shy, slow-moving species. Shrimp eaters may also prey on very small nano fish.

The safe temperature window for both species falls between 24°C and 28°C. Aim for the midpoint of this range (around 26.0°C) for optimal comfort.

The pH requirements of Cardinal Tetra (4–7) and Green Spotted Puffer (Brackish) (7.5–8.5) do not overlap, making it impossible to satisfy both species simultaneously.

Hardness requirements are incompatible: Cardinal Tetra needs 1–8 dGH while Green Spotted Puffer (Brackish) requires 12–30 dGH.

Crucially, these species require different water types — one needs freshwater while the other requires brackish conditions. This is a hard barrier to keeping them together.

To house Cardinal Tetra and Green Spotted Puffer (Brackish) together, plan for an aquarium of at least 137 litres with a minimum length of 80 cm. This accounts for the larger species' space requirements with an additional 20 % buffer to reduce territorial tension.

Providing a mix of open swimming space and sheltered areas with rocks, driftwood, or plants will keep both species comfortable and allow natural behaviour.

Specific environmental needs for this combination include: Leaf Litter/Blackwater, Driftwood (Digestion/Hiding), Plants - Densely covered, Sand (Sifters), Shells (Breeding/Hiding). Meeting these requirements will help both species thrive.

Both species do well with low (still water) water movement, so a standard filtration setup rated for the tank volume should suffice.

Feeding time deserves special attention with this pairing. Green Spotted Puffer (Brackish) is a known shrimp eater and may prey on small invertebrates or nano fish like Cardinal Tetra.