Oreochromis aureus

Native to northern Africa and the Middle East, the Blue tilapia (Oreochromis aureus) is also known as Israeli tilapia. In addition to being a popular food fish it is also raised as bait fish and some aquarists keep it as a pet.    

Geographical range
Oreochromis aureus is native to tropical and subtropical Africa and the Middle East and can be found in Cameroon, Chad, Egypt, Israel, Jordan, Mali, Niger, Nigeria, Saudi Arabia and Senegal.

Due to its popularity as a food fish, Oreochromis aureus has been introduced to many other countries outside its native range, including parts of South East Asia and the Americas. Compared to most other tilapias Oreochromis aureus is very cold tolerant and can survive even in (warm) temperate regions.

Despite being considered a freshwater species, Oreochromis aureus is also found in brackish environments and in a few locations it has even adapted to life in marine conditions. As mentioned above it is remarkably resilient to cold compared to most other tropical fishes and it occurs in waters ranging in temperature from 8 to 30 °C (47 to 86 °F). It also handles high temperature well and experiments have shown that it tolerates water temperatures up to 41 degrees C (106 degrees F). If the temperature drops below 20-22 °C (68-72 °F) the Blue tilapia won’t spawn.

Within its native range, the Blue tilapia can be encountered in environments such as the Lower Nile, the Chad Basin, the middle and upper Niger, and the Jordan Valley. It is present in open water as well as in habitats filled with densely grown aquatic plants and this species will thrive in anything from large rivers and lakes to streams, ponds and impoundments.

Conservation status
Oreochromis aureus has not been evaluated for the IUCN Red List of Threatened Species.

Oreochromis aureus as an invasive species
Oreochromis aureus is an amazingly adaptable species and this can cause problems for local flora and fauna when the Blue tilapia is introduced to ecosystems outside its native range. Since the Blue tilapia is more cold tolerant than most other tropical fish species, the risk of it spreading into new environments is also greater since it can survive in subtropical and even warm temperate climates. In addition to this, it can live in fresh, brackish and marine waters. Studies even indicate that the Blue tilapia become even more resilient to cold when living in brackish conditions (5 ppt salinity) instead of freshwater. It should however be noted that even though Oreochromis aureus can survive periods of cold weather it won’t commence breeding until the water have warmed up to at least 20-22 °C (68-72 °F), which is a limiting factor for its spread into temperate environments.

Size and appearance
The maximal published weight for an Oreochromis aureus tilapia is 2,010 grams (about 4.4 lbs) and the species can grow to a length of 18 in (about 45 cm).

During the breeding period, the head of the male tilapia will develop a bright metallic blue shade while a vermilion colour appears on the edge of his dorsal fin. The margin of his caudal find will become intensely pink. The breeding dress of the female Blue tilapia features orange dorsal- and caudal fin edges.

Social behavior
Blue tilapias live together in schools in the wild, but can become territorial during the breeding period.

Young specimens have a varied omnivore diet while adult fish tend to be fairly strict herbivores. The young fish is quite opportunistic and will for instance readily gulp down copepods, cladocerans and small invertebrates. Adult fish is more picky and will typically stick to phytoplankton and epiphytic algae, with occasional servings of zooplankton. The killing and eating of small fish has been observed in some individuals but we do not know how widespread this practise is. The Blue tilapia is a flexible species that will adapt its diet to the environment, so tilapias faced with a shortage of plankton or an abundance of easily succumbed fish may very well become more piscivore than otherwise.
The female Oreochromis aureus usually attains sexual maturity when she’s roughly 10 cm (4 inches) long, but reports of smaller females with ripe ovaries do exist.   

Mouthbrooding is a common behaviour in African cichlids and Oreochromis aureus is no exception. The male will defend his breeding territory through displays and, if necessary, mouth fighting.  He will also build a nest and the female will place her eggs in it. Once the eggs have been fertilized, the female will pick them up with her mouth since the Blue tilapia is a maternal mouthbrooder. She will then swims to deeper waters and wait for the offspring to grow large enough to be released. The eggs hatch inside her mouth but the fry isn’t let out until she deems them big enough for the world outside.

Oreochromis aureus won’t reproduce if the water temperature is below 20-22 °C (68-72 °F).