Blue Tilapia, Oreochromis aurea
The Blue Tilapia, Oreochromis aurea, whose Spanish common name is tilapia azul, is a species in the family Cichlidae, the Cichlids and Talapias, are known as tilapias and mojarras de agua dulce in Mexico. They are also known as the Israeli Tilapia. They are native to the Middle East and Northern and Western Africa and via human introductions they are now found throughout the 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 1960s with fish being imported from Israel.
The adult Blue Tilapia has an overall “bluegill profile” with deep bodies that are approximately 40% of body length. Juveniles have grey vertical bars on their sides and the caudal fin may have vertical bars. Adults are blue-gray in color being darker above and white ventrally. They many have dark vertical bars on the body. The heads have small terminal mouths with numerous small teeth and eyes that have a red iris that is crossed by a black bar. The anal (three spines and eight to eleven rays) and caudal fins have white spots posteriorly and the caudal fin has a red margin. The dorsal fin has fourteen to seventeen spines and eleven to fifteen rays and is dark and 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 to their caudal and dorsal fins. A key to identification is that they have 18 to 26 lower gill rakers on the lower arch. The body is covered with cycloid scales.
The Blue Talapia are found in rivers and lagoons predominantly in fresh water that are both low and high flow but they can also tolerate fairly high levels of salt and are also found in brackish waters. They prefer soft bottoms. They are a schooling species except during breeding season. They are found in shallow water during the day and retreat to deeper waters at night. They are residents of all Mexican freshwater environments that have temperatures between 13o and 30oC. They weight 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 cm (5 inches) to 20 cm (8 inches) and weigh 2.3 kg (5 pounds) to 2.7 kg (6 pounds). The Blue Tilapia are herbivorous primarily consuming 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 20oC with each female raising multiple broods per year. Males establish breeding territories by excavating substrate normally in shallow water weedy areas and in clusters. They become highly aggressive and will defend the 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 by the male the female collects the eggs and stores them in her mouth (mouthbrooding) and leaves the nest. The males then try to attract another female. The eggs hatch in three days and then are retained in the mothers’ 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 the mouth for protection as needed. The Blue Tilapia have lifespans of up to 5 years.
Blue Tilapia 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 as they can use atmospheric oxygen, and general pollution. They can grow and reproduce in waters with a relative high salt content. They cannot survive in waters that are less than 10oC. The Blue Tilapia is a popular food fish with white, mild flesh and they are marketed live, fresh and frozen. In general they are deemed to be a boon to local communities providing a low priced protein food and employment opportunities for local 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 being a small player in this global market.
Blue Tilapia can be easily confused with the Mozambique Tilapia, Oreochromis mossambicus (16 – 22 gill rakers) and the Redbelly Tilapia, Tilapia zilli (8 – 10 gill rakers on first arch).
The Blue Tilapia has not been evaluated from a conservation perspective. Indications are however, that it is a stable species and not prone to hybridization in the wild that would lead to its long term extinction. They have been introduced to many new global locations for a food source, aquatic plant control, and as a bait fish and a sport fish. They are also used in waste water holding ponds from fossil fuel and nuclear generated based energy facilities to help cool the warm waters. They have escaped from aquaculture facilities, experimental control areas, aquarium releases and have been released from bait buckets by recreational anglers. The Blue Tilapia provide strong competition with native fishes for food, nesting space including the direct consumption of small fishes and have been blamed for the eradication of all plant life in some water systems. As such the Blue Tilapia are now established in ten states in the United States where they are considered to be 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 species become increasingly aggressive. They are readily available alive via the WWW from United States based farms with one-inch fish priced at about $1.00 each.