Marilynae Pencilfish

Nannostomus marilynae is one of the most specialised and sought-after pencilfish, restricted to the upper Rio Negro blackwater system in northwestern Brazil. Its most striking feature is the vivid red stripe running along the lower flank, contrasting against the dark mid-lateral band and pale dorsal area. The combination of colours is breathtaking in an optimised blackwater setup.

This species demands rigorous water quality: near-zero hardness, very low pH, and organic tannin content mimicking the black rivers of its origin. It is extremely sensitive to fluctuating parameters and unsuitable for community tanks that don't meet these criteria. A dedicated blackwater species tank is strongly recommended.

Feeding should focus heavily on live and frozen micro-foods: baby brine shrimp nauplii, rotifers, micro-worms, and daphnia. Micro-pellets may be accepted by acclimatised individuals. Patience and attention to detail are rewarded with one of the most spectacular pencilfish available to the hobby.

Water: 23–27°C, pH 4.5–6.0, ultra-soft (GH 0–4, KH 0–2); RO or rainwater essential; heavy tannin staining. Tank: 40 L minimum; blackwater species tank, peat-filtered, very dim lighting, dense planting. Feeding: Baby brine shrimp nauplii, rotifers, micro-worms, daphnia; finest micro-pellets occasionally. Breeding: Rarely achieved; ultra-soft acidic water, meticulous conditioning, and live-food diet required. Compatibility: Species tank only — other Rio Negro nano fish of similar delicacy if any companions are used.