Species profile
Coral Red Pencilfish
Nannostomus mortenthaleri
Peaceful
Hard care
60 L minimum aquarium
2.5–3.5 cm adult size
Top mid
Minimum group: 10
About this species
General notes for hobby use.
A soft-water specialist. Stable mature conditions and very low mineral load are more important than chasing the smallest possible tank.
Water parameters
Suggested general range for long-term care.
Temperature
24–28 °C
pH
4.5–6.5
GH
0–5 dGH
KH
Not yet documented
Flow preference
Low
Data confidence
Verified
Behaviour
General behaviour traits used by TanksConnected compatibility checks.
Minimum group size
Minimum group: 10
Tank zone
Top mid
Territory level
Low
Predation risk
Tiny fry
Bioload factor
0.35
Peaceful overall, though males display and can spar. Keep a substantial mixed-sex group with visual cover.
Compatibility flags
Quick cautions for common tank-planning issues.
Fin nipper
No
Plant safe
Yes
Shrimp safe
Yes
Snail safe
Yes
Cave breeder
No
Digs substrate
No
Jump risk
Yes
Natural history & care
Research-backed context for long-term aquarium care.
Lifespan
Not yet documented
Diet type
Omnivore
Minimum aquarium volume
60 L
Minimum footprint
60 × 30 cm
Accepted scientific name
Nannostomus mortenthaleri
Alternative names
Coral Red Pencilfish, Red Arc Pencilfish
Native range
Peruvian Amazon, especially blackwater tributaries in the Nanay region.
Natural habitat
Very soft, acidic blackwater-style aquarium with botanicals, floating cover and gentle flow.
Diet & feeding
Tiny live/frozen foods are especially useful; also accepts suitably small quality dry foods once settled.
Breeding & sexing
Research-backed guidance for identifying sexes and reproductive behaviour.
Sexing
Males show stronger red/black patterning and are slimmer; females are rounder and less intensely coloured.
Breeding
Egg-scatterer; successful breeding generally uses very soft acidic water and dense fine-leaved cover.