Can Arrowhead Puffer and Least Killifish (Heterandria) Live Together?

Arrowhead Puffer is a highly aggressive species (10/10), while Least Killifish (Heterandria) is peaceful (1/10). This notable difference means Arrowhead Puffer may occasionally assert dominance over Least Killifish (Heterandria).

Large aggression gap (9 points) between Arrowhead Puffer and Least Killifish (Heterandria) increases stress risk for the more peaceful fish.

Arrowhead Puffer and Least Killifish (Heterandria) both frequent the Bottom (Substrate) region of the setup. This overlap can increase competition for space, so providing ample room and cover is important to keep both species comfortable.

There is a critical concern: the Piscivore (Eats small/nano fish) behaviour of one fish directly conflicts with the Nano / Bite-sized (Predation Risk) trait of the other — piscivorous fish will prey on nano-sized tank mates..

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 22°C and 27°C. Aim for the midpoint of this range (around 24.5°C) for optimal comfort.

Both fish can tolerate a pH between 7 and 7.5. Maintaining a stable value within this band is more important than hitting an exact number.

For general hardness, the shared comfort zone is 5–15 dGH. Regular testing will ensure conditions stay within this range.

To house Arrowhead Puffer and Least Killifish (Heterandria) together, plan for an aquarium of at least 114 litres with a minimum length of 75 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: Sand (Sifters), Plants - Densely covered, Plants - Floating. 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.

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