Can Goldfish (Comet / Common) and Least Killifish (Heterandria) Live Together?

Both Goldfish (Comet / Common) and Least Killifish (Heterandria) are peaceful species with an aggression score of 1/10. Their matching temperaments mean neither fish is likely to dominate the other in a shared aquarium.

Goldfish (Comet / Common) and Least Killifish (Heterandria) both frequent the Top (Surface), Middle (Open Water), and 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.

Additional behavioural considerations to keep in mind: Hyperactive swimmers can stress shy, slow-moving species through constant motion. Aggressive eaters may outcompete shy fish for food, leading to malnutrition.

To improve the chances of a peaceful coexistence in this community tank: A larger aquarium with ample hiding spots can help diffuse aggression and give the less dominant fish space to retreat.

The safe temperature window for both species falls between 18°C and 24°C. Aim for the midpoint of this range (around 21.0°C) for optimal comfort.

Both fish can tolerate a pH between 7 and 8. Maintaining a stable value within this band is more important than hitting an exact number.

For general hardness, the shared comfort zone is 5–20 dGH. Regular testing will ensure conditions stay within this range. An aquarium test kit is recommended for monitoring.

To house Goldfish (Comet / Common) and Least Killifish (Heterandria) together, plan for an aquarium of at least 240 litres with a minimum length of 120 cm. This accounts for the larger species' space requirements with an additional 20 % buffer to reduce territorial tension.

Because this pairing requires extra vigilance, include plenty of hiding spots — caves, driftwood, and dense plant clusters — so the less dominant fish can retreat when needed.

Specific environmental needs for this combination include: Sand (Sifters), Smooth Gravel (Sensitive Barbels), Plants - Densely covered, Plants - Floating. Meeting these requirements will help both species thrive.

Note a potential conflict in setup requirements: Goldfish (Comet / Common) is a plant destroyer, which conflicts with Least Killifish (Heterandria)'s requirement for live plants. Compromise where possible or prioritise the more critical need.

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. Goldfish (Comet / Common) is an aggressive eater that may prevent Least Killifish (Heterandria) from getting enough food.

Because Goldfish (Comet / Common) is a fast, competitive feeder, consider using sinking pellets or feeding at opposite ends of the setup to ensure Least Killifish (Heterandria) receives an adequate share.