Can Beckford's Pencilfish and Bucktooth Tetra (Exodon) Live Together?

Beckford's Pencilfish is a peaceful species (2/10), while Bucktooth Tetra (Exodon) is highly aggressive (9/10). This notable difference means Bucktooth Tetra (Exodon) may occasionally assert dominance over Beckford's Pencilfish.

Large aggression gap (7 points) between Beckford's Pencilfish and Bucktooth Tetra (Exodon) increases stress risk for the more peaceful fish.

Beckford's Pencilfish and Bucktooth Tetra (Exodon) both frequent the Top (Surface) and Middle (Open Water) 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 are critical concerns: the Nano / Bite-sized (Predation Risk) behaviour of one fish directly conflicts with the Piscivore (Eats small/nano fish) trait of the other — piscivorous fish will prey on nano-sized tank mates.. Additionally, the Shy / Slow Moving (Easily Stressed) behaviour of one fish directly conflicts with the Eye Biter (Attacks slow moving fish) trait of the other — eye biters attack slow-moving fish, risking permanent injury..

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.

Worth noting: Beckford's Pencilfish is a known jumper, so a tight-fitting lid is essential.

The safe temperature window for both species falls between 23°C and 28°C. Aim for the midpoint of this range (around 25.5°C) for optimal comfort.

Both fish can tolerate a pH between 5.5 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 1–15 dGH. Regular testing will ensure conditions stay within this range.

To house Beckford's Pencilfish and Bucktooth Tetra (Exodon) 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.

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 - Densely covered, Plants - Floating, Leaf Litter/Blackwater, Driftwood (Digestion/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.