The tiger barb, from the slow rivers of Sumatra and Borneo, is an orange-gold fish crossed by four bold black bars, growing to about two and a half inches. It is also the fish that taught generations of aquarists the phrase fin-nipper. Tiger barbs are not evil and they are not even unusually aggressive for a barb; they are intensely social, perpetually active and hardwired to test anything that drifts past. Kept correctly they are one of the most entertaining fish in the hobby. Kept in a pair, they are a slow-motion disaster for everything else in the tank.
The school is the whole strategy
A tiger barb's aggression is really hierarchy maintenance, and hierarchy needs a crowd. In a school of eight to ten or more, every barb has rivals above and below it, the sparring is constant and ritualised, and almost none of it lands on other species. Drop the group to three or four and the same fish, with too few rivals to occupy them, redirect everything onto their tank mates. This is why tiger barb advice always starts with a number rather than a species list, and why adding two barbs to an existing calm community is the worst possible way to keep them.
Companions with the speed and confidence to cope
Other barbs are the backbone of a tiger barb tank: rosy, gold and green tiger barbs all match the tempo, and green tigers are the same species in another colour, so mixed groups school together. Zebra danios are too fast to catch and too busy to care, and rainbowfish bring size and speed in the upper water. Yoyo loaches and, in genuinely large tanks, clown loaches hold the bottom with total indifference. Corydoras go unmolested thanks to their armour, and short-finned platies and swordtails are quick enough to stay ahead of trouble. A single red-tailed shark in a large tank can also hold its own, though that pairing deserves watching in the first week.
The never list
Angelfish are the worst possible choice, slow and draped in the exact finnage tiger barbs exist to trim. Bettas cannot escape and will not stop being tested, guppies lose their tails within days, and gouramis trail delicate feelers that barbs treat as targets. Shy fish fail differently: nothing injures them, but the barbs' constant motion and mob feeding keep them hidden and hungry. Any long-finned bred variety of an otherwise suitable fish belongs on the never list too, because it is the fins, not the species name, that create the problem.
Space, plants, and feeding the mob
Give an adult school thirty gallons or more, planted in clumps that break the tank into sections, with open water between for the group's circuits and races. Water between 74 and 79°F with a pH from 6.0 to 7.5 keeps them comfortable, and they are unfussy eaters that should be fed across a wide area so the whole school spreads out instead of mobbing one corner. Through the KinsLe Pet Services Directory you can find a store that will reserve a full tiger barb school, so the group arrives together and settles as one.