Can Clown Killifish and Figure 8 Puffer (Brackish) Live Together?

Clown Killifish is a peaceful species (2/10), while Figure 8 Puffer (Brackish) is semi-aggressive (8/10). This notable difference means Figure 8 Puffer (Brackish) may occasionally assert dominance over Clown Killifish.

Large aggression gap (6 points) between Clown Killifish and Figure 8 Puffer (Brackish) increases stress risk for the more peaceful fish.

In terms of spatial distribution, Clown Killifish prefers the Top (Surface) zone, whereas Figure 8 Puffer (Brackish) occupies the Middle (Open Water) and Bottom (Substrate) zones. Because they use different levels of the water column, territorial disputes are less likely and the tank will appear more balanced.

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

Worth noting: Clown Killifish is a known jumper, so a tight-fitting lid is essential.

The safe temperature window for both species falls between 24°C and 27°C. Aim for the midpoint of this range (around 25.5°C) for optimal comfort.

The pH requirements of Clown Killifish (5–7) and Figure 8 Puffer (Brackish) (7.5–8.5) do not overlap, making it impossible to satisfy both species simultaneously.

Hardness requirements are incompatible: Clown Killifish needs 1–8 dGH while Figure 8 Puffer (Brackish) requires 10–25 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. An aquarium test kit is recommended for monitoring.

To house Clown Killifish and Figure 8 Puffer (Brackish) together, plan for an aquarium of at least 72 litres with a minimum length of 60 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: Plants - Floating, Plants - Densely covered, Leaf Litter/Blackwater, 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. Figure 8 Puffer (Brackish) is a known shrimp eater and may prey on small invertebrates or nano fish like Clown Killifish.