Blue danio

The blue danio (Brachydanio kerri, formerly Danio kerri) is a small, active cyprinid native to southern Thailand and the northern Malay Peninsula. It inhabits clear, well-oxygenated forest streams and small rivers with substrates of rocks, boulders, and gravel, where submerged surfaces are often carpeted with rich biofilm and marginal vegetation grows thickly. Populations from different localities vary noticeably in body colouration: those from the northern end of the range tend to exhibit a striking blue hue while southern populations appear more yellowish. Males are generally more colourful and slightly smaller than the rounder-bellied females. This species reaches a maximum standard length of 40 to 45 mm and is very peaceful, making it an ideal resident of the well-researched community aquarium. It is a tightly schooling fish that should be maintained in groups of at least 8 to 10 individuals. The tank should be generously planted with a darker substrate and have ample open swimming space, with base dimensions of at least 80 × 30 cm (approximately 72 litres). A tight-fitting cover is essential as this species is an accomplished jumper. The blue danio is chiefly insectivorous in nature — feeding on aquatic and terrestrial insects and their larvae — but readily accepts quality dried foods supplemented with live and frozen bloodworm, Daphnia, and Artemia in captivity. It is compatible with a wide range of popular community fish including tetras, livebearers, rainbowfishes, and other small cyprinids.