Can Ceylon Puffer (Brackish) and Clown Killifish Live Together?

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

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

In terms of spatial distribution, Ceylon Puffer (Brackish) prefers the Middle (Open Water) and Bottom (Substrate) zones, whereas Clown Killifish occupies the Top (Surface) zone. 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 Ceylon Puffer (Brackish) (7.5–8.5) and Clown Killifish (5–7) do not overlap, making it impossible to satisfy both species simultaneously.

Hardness requirements are incompatible: Ceylon Puffer (Brackish) needs 12–30 dGH while Clown Killifish requires 1–8 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 Ceylon Puffer (Brackish) and Clown Killifish together, plan for an aquarium of at least 150 litres with a minimum length of 90 cm. This recommendation combines the stricter species minimums with a community-load allowance so the pairing has realistic long-term space and filtration headroom.

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: Shells (Breeding/Hiding), Sand (Sifters), Plants - Floating, Plants - Densely covered, Leaf Litter/Blackwater. Meeting these requirements will help both species thrive.

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

Ceylon Puffer (Brackish) and Clown Killifish are the kind of pair that can look acceptable in a shop but become a maintenance problem at home. The main risk is not a single number in the chart; it is the way incompatible behavior, water needs, or pressure on space compounds over time once both fish are established in the same tank.

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