Cosmic Blue Danios (Danio rerio) are a GloFish variant of the Zebra Danio with a vivid fluorescent blue body that catches light vividly as the fish moves through the water column. The colour is produced by an inserted fluorescent protein gene and does not fade over the fish's lifetime, unlike dyed or painted fish. Active, hardy, and tolerant of a wide range of water parameters, they are one of the more straightforward nano fish to keep long-term and one of the most visually striking at their size. The cool blue colouration creates a striking contrast against warm-toned shrimp like Fire Red Cherry or Sunkist in a planted display tank.
6.5–7.5pH
4–12GH (dGH)
65–75°FTemperature
1 inMax Size
Appearance & Behaviour
Iridescent Blue in Motion
Luminous iridescent blue body that shifts and flashes with movement. Like the Neon Tetra, the blue of the Cosmic Blue Danio is structural rather than purely pigment-based, producing an intensity and depth of colour that changes as the fish moves and the light angle shifts. In a group the collective shimmer of a school turning in synchrony is one of the most visually engaging effects a nano tank can produce.
Active, energetic schooling behaviour throughout the full water column. Cosmic Blue Danios are more active and cover more of the tank than the mid-level-preferring CPD or the surface-oriented White Cloud. They move through upper, mid, and lower zones of the tank, which gives a planted display tank consistent movement at every level. Their energy level is higher than most nano fish but not disruptive to calmer tankmates.
School of 6 minimum, 10 or more for best behaviour and colour display. Like all danios, Cosmic Blues school more tightly and show better colour in larger groups. A school of 10 in a 10 to 20-gallon planted tank produces confident, active behaviour and the full collective shimmer effect the species is known for.
Hardy and tolerant of a wide parameter range -- one of the more beginner-friendly nano fish. Cosmic Blue Danios tolerate pH 6.5 to 7.5 and moderate hardness, covering the standard Neocaridina range comfortably. They are more forgiving of parameter fluctuations than CPDs or Chili Rasboras and recover well from minor water quality events in an established tank.
Shrimp Compatibility
Good Companion with Planted Cover
Adult Neocaridina shrimp are safe -- shrimplets are at moderate risk. Cosmic Blue Danios are active and will investigate and consume shrimplets. Adult shrimp at full size are too large to be targeted. In a heavily planted tank with abundant fine-leaved plant cover and moss, shrimplet survival rates are adequate for maintaining a breeding colony alongside the fish. In a sparse tank shrimplet survival will be low.
Cool blue colouration creates strong visual contrast with warm-toned shrimp. The iridescent blue of the Cosmic Blue Danio reads as a direct visual counterpoint to red, orange, and yellow Neocaridina morphs. A school of Cosmic Blues with a colony of Fire Red Cherry or Sunkist shrimp on dark substrate produces a warm-cool contrast that is immediately striking and that works at every scale of observation.
Temperature overlap with Neocaridina is excellent. Cosmic Blue Danios prefer 65 to 75°F, which aligns closely with the Neocaridina preference of 65 to 78°F. No heater compromise is required and both species perform well in the 68 to 74°F range that suits each comfortably.
Keeper's NoteCosmic Blue Danios paired with Fire Red Cherry or Sunkist shrimp on black sand substrate with green planted background is one of the most straightforward high-impact display combinations available in the nano tank hobby. The blue-and-red or blue-and-orange contrast between fish and shrimp is complementary in the colour theory sense -- cool against warm -- and both species are beginner-friendly, hardy, and available. Plant densely with Java Moss and Rotala in the background, add the Danios first and let the tank settle for two weeks before introducing shrimp.
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