Nile Tilapia, Oreochromis niloticus
The Nile Tilapia, Oreochromis niloticus, whose common Spanish name is tilapia del Nilo, is a species in the Cichlid and Tilapia or Cichlidae Family, known collectively as tilapias and mojarras de agua dulce in Mexico. They were named by Aristotle in 300 B.C. and reportedly fed by Jesus to the multitudes during the Sermon on the Mount. They are native to Africa, from Egypt to Cape Horn and via human introductions are now found throughout global tropical and subtropical locations. Globally, there are thirty-two species in the genus Oreochromis, four of which are found in the majority of freshwater systems within Mexico. They were introduced and cultivated in Mexico in the 1970s with fish being imported from Brazil.
Adult Nile Tilapias have an overall “bluegill” profile with deep compressed bodies that are approximately 40% of body length. Juveniles have gray vertical bars that extend down the body to the bottom edge of the caudal fin which also has vertical bars. Adults have a blue-gray coloration and are darker dorsally and white ventrally. They have many dark vertical bars on their body. The margin of their dorsal fin is gray to black and their throat is generally gray with a pink pigmentation. Breeding fish have reddish caudal, dorsal, and pectoral fins with their caudal fin having numerous black bars. They have small terminal mouths with numerous small teeth. Their anal fin has 3 spines and 9 to 11 rays; their caudal fin is straight; and their dorsal fin is continuous with 15 to 18 spines and 11 to 13 rays. A key to identification are the 27 to 33 gill rakers on their lower arch. Their lateral line is interrupted and their body is covered with cycloid scales.
The Nile Tilapias are found in slow-moving water bodies including streams, lakes, sewage canals, and irrigation channels generally near shore at depths up to 20 feet in warm water as they avoid the deeper colder waters. They weigh up to 4.3 kg (9.5 pounds) and the maximum recorded length is 60 cm (24 inches) with males being two times larger than females. They are predominately a fresh water species but can tolerate fairly high levels of salt, thus are also found in brackish waters. They are a schooling species except during breeding season. They are found in waters that range from 46oF (8oC) to 108oF (42oC). They are omnivores and consume predominately algae, plankton, and plant materials and to a lesser extent small invertebrates. Reproduction is prolific and occurs year-round when water temperatures are in excess of 75oF (24oC) with each female capable of raising multiple broods per year. Males are larger than females and fight with other males for territories with dominant males obtaining access to increased amounts of food and more mates. Males establish breeding territories by excavating firm sand substrate to depths of six feet. Each female will lay 100 to 1,500 eggs. After fertilization by the male the female collects the eggs and stores them in her mouth (mouthbrooding) for twelve days. After hatching the young remain in close proximity to their mother and can re-enter her mouth for protection as needed. They have a lifespan of up to ten years.
The Nile Tilapias are the number one farmed tilapia in the world and are now farmed in at least 100 countries. They are hardy individuals that are highly adaptable to new environments, differing water conditions, brackish waters, changes in food supplies, and have a tolerance for high levels of ammonia, low levels of oxygen (they can use atmospheric oxygen), and general pollution. They are a popular food fish with mild white flesh and are marketed live, fresh and frozen. In general they are deemed a boon to local communities providing a low-priced protein source and employment opportunities for residents. This species is produced at a level of two million tons per year and constitutes about 70% of the total global tilapia aquaculture production with China producing over 50% of the total followed by Egypt, the Philippines, Thailand, and Indonesia. Mexico is currently not a major global player in this market being plagued by non-competitive production costs, noting that accurate global information in this area is exceedingly sparse. The farming of the Nile Tilapia dates to ancient Egypt as documented by bas-relief from an Egyptian tomb that dates to at least 4,000 years ago. Farmed fish suffer from a lack of genetic variability attributed to rapid reproduction rates (fry can develop to sexual maturity in five to six months) and inbreeding that generates stunted fish in crowded environments and leads to cannibalism.
In Mexican waters the Nile Tilapia can be found in all fresh water systems of the country.
The Nile Tilapia can be easily confused with the Blue Tilapia, Oreochromis aureus (16 to 22 gill rakers).
The Nile Tilapias have not been evaluated from a conservation perspective. Indications are that this species is stable and not prone to hybridization in the wild, thus protecting it from long-term extinction. They have been introduced to many new global locations as a food source, for aquatic plant control, and as bait and sport fish. They have escaped from aquaculture facilities, experimental control areas, and aquarium releases and have been released from bait buckets by recreational anglers. They provide strong competition with native fish for nesting space and food including the direct consumption of small fish and have been blamed for the eradication of all plant life in some water systems. As such they are now established in at least six states in the United States where they are considered an invasive pest capable of causing significant environmental damage. They can be used as aquarium fish, however they become excessively large very quickly. They are also a dirty fish that require frequent water changes and older specimens become increasingly aggressive. They have been studied extensively with strong efforts towards improving the quality of farmed fish, however their potential is hampered by their dark flesh, their intolerance to low water temperatures, and their reputation for being a trash fish. As many as eight hybrids have been created, one of the most popular being the “Rocky Mountain White” which has white flesh and a tolerance for low water temperatures. They are available from several internet vendors at a price of approximately $1.00 for a half-inch fish.
The Nile Tilapias are the predominant tilapia sold as fresh or frozen fillets as skin-on, skin-off, deep-skinned, individually quick frozen, smoked, and sashimi grade in United States markets. Live, whole, and gutter fish are available in ethnic markets. They are prepared salted, grilled, deep-fried, steamed, pan-fried, or grilled. They are also used in leather goods for clothing and accessories, time-released medicines, and flower ornaments. Due to their poor taste, they are normally tested before preparation for marketing. Fish with unacceptable flavor are purged in clean-water holding tanks for three to seven days. Dark colored fish are normally cooked with darkly colored spices to mask their color or prepared with spicy seasonings to mask their taste. They have been used in some African countries for mosquito control to try to control malaria.
Most of the future production of tilapia is expected to be attributed to the Nile Tilapia. Major on-going research is focused on developing faster growing strains that are more temperature-tolerant and disease-resistant and can be produced in adequate size on low cost hormone-free feeds.
Nile Tilapia, Oreochromis niloticus. Fish caught by hand out of the Cabo Real Golf Course irrigation pond, Cabo Real, Baja California Sur, February 2005. Length: 15 cm (5.9 inches). Identification courtesy of Dr. Ross Robertson, Smithsonian Tropical Research Institute, Panama.