Celebes rainbowfish

Celebes rainbowfish come from clear, slow-flowing streams in the island of Sulawesi, Indonesia, and are the sole species in the genus Marosatherina. Males reach about 8 cm standard length and develop striking iridescent blue-green flanks, a yellow dorsal fin, and elongated extensions to the second dorsal and anal fin rays, attributes that make them one of the more elegant rainbowfish in the hobby. Females are noticeably plainer and smaller. A 70-litre tank is adequate for a small shoal of six to eight, though larger is always better. They need a well-planted setup with floating plants to diffuse the light and open swimming space in the middle layers. Water should be neutral to alkaline (pH 7.0–8.0) and medium-hard to hard; they will not thrive in soft, acidic conditions. Temperature of 22–28°C covers their needs, and while they can tolerate mildly brackish conditions, salt is not required despite what some older literature claims. They are sensitive to rapid water chemistry swings, so slow acclimation and regular weekly water changes of moderate volume are important. Celebes rainbowfish are peaceful and shoaling — keep them in groups of eight or more, with two to three females per male to spread male attention and allow the best colour displays. They accept most dried, frozen, and live foods; a varied diet brings out the best colouration. Breeding is an egg-scattering affair over several weeks, with eggs hatching in 5–10 days; fry need infusoria initially.