With some 960-1200 species,(1,2) the characids, sometimes called characins,(1,3,4) are the fourth-most-diverse fish family.(2) These freshwater fish can be found from Texas, USA (1,3) all the way down to the northern part of Patagonia in Argentina,(2) in streams, rivers, and even underwater caves,(3,4,5,6) but the greatest variety of species occurs in the basins of the Amazon, La Plata, and Orinoco rivers.(2) The group’s diversity and the dispute over its delineation (2,7) make it difficult to state its defining characteristics; characids range in length from under 3 cm(1,3) to over 100 cm,(1) come in many different colors and patterns, and have varying habits.(4) Some, most notably some piranhas, are fierce predators.(4,7) Others often eat fruits that have fallen off of rainforest trees and disperse the seeds, unintentionally helping the trees reproduce.(4,6) Some characids are used as food sources by humans,(1,4) and some, such as the small brightly-colored tetras and the flying fish known as hatchetfish, are popular choices for aquariums.(1,3,4,7)