The leopard danio is the spotted variety of the zebra danio, its stripes broken into gold spots scattered over a blue-silver body. It grows to about two inches and spends its life in near-constant motion at the surface, weaving through the top few inches of the tank in a loose, tireless school. Leopard danios are almost indestructible as fish go, tolerating a wide range of temperatures and water chemistry, so the stocking question is never about what they can survive; it is about what can survive living with them.
Life in the fast lane
Danios are built for current and open water, and a leopard danio school treats the whole surface as a racetrack. That energy is the filter every candidate tank mate has to pass through. Fish of similar speed treat it as background noise, but slow or territorial species experience a danio school as a permanent disturbance passing through their space every few seconds. Leopard danios also feed explosively at the surface, which means anything that eats slowly or nervously in the upper water will go hungry in their company no matter how peaceful the tank looks.
Companions that keep up
Other danios are the first answer: zebras, pearls and leopards mix freely and often school as one. White cloud mountain minnows share the leopards' love of cooler water and hold their own at the surface. Gold and rosy barbs patrol the middle with enough confidence to ignore the traffic above them. The trick that makes a danio tank work, though, is filling the lower storeys separately: corydoras and weather loaches live on the bottom in a completely different world, untouched by the racing overhead and fed on sinking foods that fall past the school.
Fish that cannot live at danio speed
Bettas fail on every count, being slow, long-finned and territorial in exactly the layer danios occupy, and fancy guppies fare little better. Shy species are the less obvious casualties: celestial pearl danios, ember tetras and other retiring fish respond to danio commotion by hiding permanently and missing meals. Centrepiece fish that stake out a calm territory, such as many gouramis, find the territory meaningless when a school crosses it forty times an hour. None of this makes leopard danios aggressive; it makes them exhausting, and exhausted tank mates decline slowly.
Lids, length, and feeding order
Leopard danios jump with intent, so a tight lid with no gap at the filter cut-out is part of the species' basic kit, and a long tank of twenty gallons or more suits their racing better than a tall one. They are happiest between 64 and 75°F, which suits their best companions too. Feed in two stages: floating food for the school first, then sinking wafers once the danios are occupied, so the bottom fish eat in peace. KinsLe's Care Teams keeps the leopard danio tank's twice-daily routine on track, so fast surface feeders and slow bottom dwellers both get their share when you are away.