Cichlids belong to the order Perciformes, which includes the largest number of species within the teleosts. The family Cichlidae includes, in general, species with a moderately high body and slight lateral compression. Like in all teleosts nostrils are paired double structures but cichlids present a single nostril opening on each side of the forehead. There is an interrupted lateral line with an anterior upper portion and a posterior lower portion and a wide-based dorsal and anal fins. They provide parental care in some species. Cichlids have a natural worldwide distribution in temperate and warm freshwaters environments, with few species living in brackish water. Due to their economic importance, angelfish and tilapias are the best known members of the family. Angelfish belong to the genus Pterophyllum and are from South American tropical freshwaters. Many of the species are small, attractively coloured and easy to breed, making them popular aquarium species. Tilapias, originally from Africa, are currently a widely distributed species in warm-temperate waters around the world. All tilapias are diurnal and prefer benthopelagic habits, they are mainly herbivorous (eating plants, algae and phytoplankton), although some may be omnivorous. They are potamodromous, sensitive to extreme temperatures, developing best in clearly warm waters. In cool-temperate waters, they do not breed below 20°C, and below 17ºC, growth stops. Infections and diseases are a higher risk when temperatures are lower than 10°C. Hormonal manipulation can be used to revert fish to males, which grow faster and are larger than females. Within their optimal temperature range (29-31°C) they are fast-growing, tolerant to high densities and a wide variation in salinity and dissolved oxygen and resistant to disease. They have a high capacity for hybridization and accept a wide range of foods. Their phenotypic plasticity, ecological adaptability and parental care of eggs and fry endow them with high reproductive yield, making them potential competitors to native fish populations and sometimes may even lead to their extinction. The most economically important genera to fisheries and aquaculture are Oreochromis and Tilapia, both of which have numerous hybrids. Tilapias can grow to a length of 60 cm, record weight of 5 kg and live as long as 11 years. Tilapias and other cichlids obtained by means of aquaculture or fisheries provide the second-largest volume after carp to the world market (~ 4.300.000 tons in 2012, FAO), with the greatest proportion provided by tilapia. They are also an important food source through small-scale and subsistence fisheries and aquaculture activities.