Peacock cichlids are bought for colour, but they should be stocked for size: the drab juvenile in the shop bag is on its way to becoming one of the larger fish in a Malawi-style aquarium.
Four to six inches, males at the top end
Most peacock cichlids mature at between 4 and 6 inches. Males reach the upper part of that range, developing the long fins and saturated blues, reds, or yellows the group is named for, while females stay nearer the smaller end and keep silvery-brown, subdued patterning for life. A few chunky types can look heavier than their length suggests because adult males fill out through the shoulder. Expect the bulk of growth within the first couple of years, with colour arriving alongside size in males; a male that stays small and pale in a crowded tank is often being suppressed by a dominant rival rather than genetically destined to stay plain.
Tank length matters more than the tape measure
A 6-inch peacock is an active, open-water swimmer over rockwork, so the tank needs horizontal swimming room and a rock structure with caves and breaks along the back, not just a large water volume in a short cube. All-male displays are popular for colour, but every added male is another 5 or 6 inches of adult claiming visual space, and overstocking slightly is sometimes used to diffuse aggression only in tanks genuinely large enough to hold the full adult group. Stock for the finished sizes on day one: a collection of 2-inch juveniles that looks sparse will, at adult size, fill the same tank completely, and removing a now-bullying adult later is a far harder conversation than stocking conservatively at the start.
Feeding adults without spoiling colour or water
Peacocks are omnivores that lean insectivorous in the wild, picking small invertebrates from sand and rock surfaces. In the aquarium a quality cichlid pellet sized for adults forms the base, with regular variety from frozen foods and some plant matter, fed in amounts the whole group finishes quickly. Overfeeding is the common adult problem: big fish produce big waste, and water quality slips fastest in heavily stocked peacock tanks, showing up as faded colour and lethargy before it shows up as obvious illness. Feed adult portions once or twice daily, keep up with generous water changes, and judge condition by body shape, where a healthy male is muscular through the back rather than pinched or bloated at the belly.
Mixing full-grown peacocks with other fish
At adult size, peacocks sit in the middle of the Malawi temperament range: assertive with each other, generally workable with similarly sized haps and robust community mates, and too boisterous for small or timid fish. Tiny tankmates risk being eaten once a male's mouth reaches adult proportions, whatever peaceful behaviour the juveniles showed. Females of different peacock types look very alike, and mixed groups can crossbreed, so keepers who care about pure lines keep one type's females per tank and note exactly what they hold. Any fish that cannot hold its own corner at feeding time will slowly lose condition beside 6-inch competitors.
Because adult size and temperament are exactly what a buyer needs to know, KinsLe Transferrable Profiles record a peacock's measured length, colour form, diet, and past tankmates, letting the next keeper stock around the real fish rather than the juvenile they imagine.