The lemon tetra comes from the Tapajos basin in Brazil and is built like a classic tetra, two inches of pale lemon-gold body with a red upper eye and bold black-and-yellow edging on the anal and dorsal fins. Its colour is a mood ring. In the right company and conditions a lemon school glows; stressed or thinly stocked, the same fish fade to a washed silver that puts people off buying them, which is a shame, because the faded version is a stocking problem rather than the fish itself.
Why lemons school tighter than most tetras
Lemon tetras hold formation more faithfully than many tetras, travelling as a unit and turning together, and they only do it in numbers. Fewer than six and the school dissolves into individuals hiding separately among the plants. Eight to ten is where the behaviour and the colour switch on, and a bigger group also means no single fish can be singled out by a pushier tank mate. Anyone choosing companions for lemons should budget for the full school first, because a half-sized lemon group makes every other decision in the tank harder.
Companions that share the middle water
Other peaceful tetras of a similar size are the backbone: ember, glowlight and rummy-nose tetras all school in the same layer without friction. Harlequin and espei rasboras bring a slightly taller body shape and the same gentle habits, and pencilfish hover near the surface in small, inoffensive groups. Corydoras and otocinclus cover the bottom and the glass between them. For a centrepiece, a honey gourami drifts at lemon speed, and a pair of apistogramma holds a bottom territory in a planted tank without troubling the school above them.
Fish that fade or frighten them
Tiger barbs and serpae tetras undo a lemon tank quickly, since lemons will not stand up to fin-testing and respond by hiding and losing colour. Large cichlids and predatory catfish eat fish of this size outright. Very fast, greedy feeders are a quieter problem, emptying the mid-water before a polite lemon school commits to eating. Stress in lemons is easy to read, which helps: if the yellow is gone and the school is pressed into the plants at midday, the company or the conditions are wrong, and the fish are telling you before anything more serious develops.
Conditions that keep the yellow showing
Lemons want soft, slightly acidic water between 73 and 82°F, with a pH from 5.5 to 7.5 and a leaning towards the lower half. A dark substrate, background planting and a slight stain of tannins in the water reproduce their home tributaries and deepen the yellow noticeably, while bare bright tanks wash it out no matter how good the company is. A varied diet with small live or frozen foods sharpens the red eye and fin edges. After any stocking change that dulls the yellow, put a follow-up question to KinsLe's Kinny; he answers using the KinsLe Answers library.