Green neon tetra

Water parameters

Tolerated range for this species. Aim for the middle of each band rather than the extremes.

Tank and habitat

Substrate: any.

Behavior

Plant interaction: plant safe.

Typically wild-caught; acclimate slowly.

Feeding

Micro pellets, crushed flake, frozen baby brine shrimp, frozen cyclops, frozen daphnia, and live micro-foods (baby brine shrimp, microworms, daphnia). The mouth is very small, even for a nano tetra. Standard-sized flake needs to be finely crushed. They feed in the midwater column and pick at floating particles. In community tanks, they're easily outcompeted by anything larger or faster. Targeted feeding near their schooling area helps. Feed twice daily in very small amounts. Live food brings out the best coloring.

Compatibility

• Extremely peaceful and tiny. At 2–2.5 cm, green neons are smaller than both neon tetras and cardinal tetras. They belong in nano setups or carefully curated community tanks.
• Best with other small, calm species: ember tetras, chili rasboras, pygmy corys, otocinclus, and shrimp. Any fish large enough to eat them will.
• Groups of 10+ are the minimum for proper schooling and color display. The neon-green stripe along the body creates a stunning effect in a large school against a dark background. Small groups look insignificant.
• Blackwater tank specialists. Green neons look their absolute best in tannin-stained water with dark substrate and subdued lighting. Under standard bright aquarium LEDs on white gravel, they lose most of their visual impact.
• Chocolate gourami: both are blackwater specialists needing very soft acidic conditions; a challenging but rewarding biotope pairing

Origin and habitat

Native to the upper Rio Negro and Orinoco basins in South America. The range covers the border areas of the mid to upper Rio Negro drainage upstream from the Rio Branco, and between the Rio Meta mouth and San Fernando de Atabapo in the Orinoco system. Exclusively inhabits blackwater environments. Originally described as Hyphessobrycon simulans by Géry in 1963. Moved to Paracheirodon by Weitzman and Fink in 1983 based on morphological similarities with neons and cardinals; this is now supported by molecular studies. The smallest of the three common Paracheirodon species: SL 1–2 cm, max about 3.5 cm overall. Distinguished from siblings by the blue-green lateral stripe extending to the tail base and minimal red coloring restricted near the tail. A fourth Paracheirodon may have been found in the rio Purus system but details are scarce. The fish changes color intensity: becoming lighter in bright conditions and duller with a violet lateral stripe at night. Range coincides with cardinal tetras but the two species are not found together.

Breeding

Not bred commercially or by most hobbyists. The species requires extremely soft, acidic water (pH below 5.5, GH effectively zero, conductivity below 30 microsiemens) that is difficult to achieve and maintain in a home setup. Wild breeding occurs during seasonal flooding when water parameters reach these extremes. Eggs are light-sensitive and fungus quickly in anything other than near-sterile, extremely soft water. A few dedicated hobbyists have reported spawning by conditioning groups in RO water acidified with peat extract, but consistent, repeatable breeding is not established. The difficulty matches or exceeds that of cardinal tetras. For the foreseeable future, all green neons will continue to be wild-caught.

Common problems

Acclimation shock is the biggest killer. Wild-caught fish coming from pH 4 water into a dealer's tank at pH 7 and then into a keeper's tank at pH 6.5 experience cumulative osmotic stress. Slow drip acclimation over 2+ hours is essential. In soft acidic water, they're surprisingly hardy once established. In hard alkaline water, they survive but show washed-out color and shortened lifespan. The species is useless as a display fish outside of soft-water setups; the green-blue stripe that makes them spectacular in blackwater conditions becomes a faint silver line under standard conditions. Ich is a risk during acclimation; treat with temperature elevation rather than chemicals. Internal parasites from wild-caught specimens cause wasting; treat with praziquantel. Neon tetra disease (Pleistophora) can affect this species as well.

Bioload

Further reading

• How to cycle a fish tank
• Stocking ideas by tank size