Blue Tilapia, Oreochromis aurea
The Blue Tilapia, Oreochromis aureus, whose common Spanish name is tilapia azul, is a species in the Cichlids and Tilapias or Cichlidae Family, are collectively known as tilapias and mojarras de agua dulce in Mexico. This fish is also known as the Israeli Tilapia. They are native to the Middle East and Northern and Western Africa and are now found throughout global tropical and subtropical locations via human introductions. 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 1960s with fish being imported from Israel, and have become highly invasive.
Adult Blue Tilapias have an overall “bluegill” profile with deep bodies that are approximately 40% of body length. Juveniles have gray vertical bars on their sides and caudal fin. Adults have a blue-gray coloration and are darker dorsally and white ventrally. They have many dark vertical bars on their body. They have a small terminal mouth with numerous small teeth. Their eyes have a red iris crossed by a black bar. Their anal fin has 3 spines and 8 to 11 rays and their caudal fin has a red margin. Both anal and caudal fins have white spots posteriorly. Their dorsal fin has 14 to 17 spines and 11 to 15 rays and is dark with light spotting on its posterior half and a red to orange upper margin. Breeding males have bright blue metallic heads, vermillion-edged dorsal fins, brightly colored caudal fins, and a blue-black chin and chest. Breeding females have light orange margins on their caudal and dorsal fins. A key to identification are the 18 to 26 gill rakers on their lower arch. Their body is covered with cycloid scales.
The Blue Tilapias are found in rivers and lagoons predominantly in fresh water (both low and high flow) but can also tolerate fairly high levels of salt, thus are also found in brackish waters. They prefer soft bottoms. They weigh up to 4.5 kg (10 pounds) and the maximum recorded length is 53 cm (21 inches) with males being larger than females; they are normally 13 to 20 cm (5 to 8 inches) and weigh 2.3 to 2.7 kg (5 to 6 pounds). They are a schooling species except during breeding season. They are found in shallow waters during the day and retreat to deeper waters at night. They are residents of all Mexican freshwater environments that have temperatures between 13°C (55°F) and 30°C (86°F). They are herbivorous and primarily consume phytoplankton and a wide variety of other materials including small crustaceans and insects on a limited basis. Reproduction is prolific and occurs year-round when water temperatures are in excess of 20°C (68°F) with each female raising multiple broods per year. Males establish breeding territories in clusters by excavating substrate normally in shallow water weedy areas. They become highly aggressive and will defend their selected territory against other males. They try to attract females from schools and lead them back to the nest. Each female will lay 160 to 1,600 eggs. After fertilization the female collects the eggs and stores them in her mouth (mouthbrooding) and leaves the nest. The males then try to attract other females. The eggs hatch in three days and are then retained in their mother’s mouth for up to two weeks when they are released as free swimming juveniles. The young remain in close proximity to their mother and can reenter her mouth for protection as needed. They have a lifespan of up to five years.
The Blue Tilapia can be found in all fresh water systems of Mexico.
The Blue Tilapia can be easily confused with the Mozambique Tilapia, Oreochromis mossambicus (16 to 22 gill rakers) and the Redbelly Tilapia, Tilapia zilli (8 to 10 gill rakers on first arch).
The Blue Tilapias are a prime farmed fish because 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 can grow and reproduce in waters with a relative high salt content, however, they cannot survive in waters that are less than 10°C. 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 60,000 tons per year and constitutes about 6% of the total global tilapia aquaculture production. Mexico is currently only a small player in this global market. The Blue 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 a bait and sport fish. They are also used in waste water holding ponds from fossil fuel and nuclear-based energy facilities to help cool warm waters. 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. They are now established in ten 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 are readily available on the internet from United States based farms with one-inch live fish priced at about $1.00 per fish.
Blue Tilapia, Oreochromis aureus. Fish caught with a cast net from the San José River, Baja California Sur, November 2008. Length: 13.0 cm (5.1 inches). Identification reconfirmed by H.J. Walker, Jr., Scripps Institution of Oceanography, La Jolla, CA.