Can Blue Dolphin (Hap) and Marbled Hatchetfish Live Together?

Blue Dolphin (Hap) is a moderately assertive species (5/10), while Marbled Hatchetfish is peaceful (1/10). This notable difference means Blue Dolphin (Hap) may occasionally assert dominance over Marbled Hatchetfish.

In terms of spatial distribution, Blue Dolphin (Hap) prefers the Middle (Open Water) and Bottom (Substrate) zones, whereas Marbled Hatchetfish 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: Hyperactive swimmers can stress shy, slow-moving species through constant motion.

Worth noting: Marbled Hatchetfish is a known jumper, so a tight-fitting lid is essential.

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 24°C and 28°C. Aim for the midpoint of this range (around 26.0°C) for optimal comfort.

Both fish can tolerate a pH between 7.5 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 10–12 dGH. Regular testing will ensure conditions stay within this range. An aquarium test kit is recommended for monitoring.

To house Blue Dolphin (Hap) and Marbled Hatchetfish together, plan for an aquarium of at least 570 litres with a minimum length of 150 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 - Floating, 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.