Oreochromis aureus (Steindachner, 1864)

Freyhof, JÖrg, Yoğurtçuoğlu, Baran, Jouladeh-Roudbar, Arash & Kaya, Cüneyt, 2025, Handbook of Freshwater Fishes of West Asia, De Gruyter : 791-793

Oreochromis aureus

Common name. Blue tilapia.

Diagnosis. Distinguished from other species of Cichlidae in West Asia by: ○ caudal usually tessellate, marbled, or with blotches not forming regularly shaped and set bars or, if bars present, then short, not reaching from upper to lower caudal rays / ○ flank scales with scales pockets darker than scale margins / ○ tip of membrane between dorsal spines orange or red / ● nuptial male bright blueish or grey with whitish lower part of head and orange dorsal and caudal margins / ○ snout not duck-bill-like, elongated in male larger than 200 mm SL / ○ anterior processes of lower pharyngeal bone clearly projecting beyond anterior margin of toothed pads / ○ chest, belly, and isthmus in front of pelvic covered by small scales / ○ chest never red / ○ 18–26 gill rakers on lower part of first branchial arch / ○ 3 anal spines / ○ scales cycloid / ○ no ocelli on anal. Size up to 380 mm SL.

Distribution. Native to Jordan drainage and lower Nile downriver of Cairo. Also native to Oued Draa drainage in southern Morocco, Senegal, central Niger and Benue, and Lake Chad basin, including lower Shari and Logone.Widely introduced in Israel, Azraq oasis in Jordan and Orontes in Syria and Türkiye, Ceyhan, Seyhan and Sakarya in Türkiye, lower Euphrates and Tigris in Iraq and Iran, Wadi Haneefah in Riyadh, Al-Kharj and Layla Aflaj south of Riyadh, and Al-Ahsa oasis in Saudi Arabia. Probably more widespread. Also established in Cyprus, Florida, South Africa, Central America, Southeast and East Asia, Hawaii, Madagascar, and elsewhere.

Habitat. Slow-flowing rivers, backwaters, lakes, and coastal lagoons.

Biology. Lives up to 5 years. Spawns in second year, usually with 160–180 mm SL. Males larger than females, and branched dorsal and anal rays longer in males. Posterior margin of dorsal membrane thickened in nuptial male. Spawning begins in late March–early April in Lake Kinneret at water temperatures above 20–22°C and lasts until late May in Kinneret or until November in Nile Delta. Males establish territories near shores in shallow water. Territory radius (0.7–3.0 m) depends on strength of male. Territories are often concentrated in leks that form breeding colonies. Within a territory, males dig a shallow nest in substrate and attempt to attract females. Eggs are laid in batches, immediately fertilised by male and taken into mouth by female. No permanent pair bond. Females may spawn with several males in a breeding colony. Females spawn several times during summer. Larvae hatch after 3 days, and females swallow eggshells. Female keeps eggs and larvae for about 13–14 days and guards free-swimming juveniles for a few more days, returning them to mouth at night. Can live in brackish water up to at least 10 ‰. Juveniles usually cannot survive temperatures below 9°C. Adults can survive night temperatures as low as 5°C for a few days if daytime temperatures are higher. Juveniles inhabit shallow habitats. Opportunistic feeders, usually phytoplankton but also zooplankton, epiphytic algae, and detritus.

Conservation status. LC.

Remarks. Very important species for aquaculture, produced in large quantities in tropical and subtropical countries and warm-water facilities in Europe. This species is often misidentified as O. niloticus or Sarotherodon galilaeus , and hybrids between these three species have been recorded in the wild. Hybrids between O. aureus and O. niloticus are produced for aquaculture.

Further reading. Trewavas 1983 (description, biology); Freyhof et al. 2020 (distribution in Saudi Arabia).

How to eliminate females in tilapias? In Oreochromis , males exhibit faster growth and greater uniformity in size than females. Consequently, the farming of monosex fish, which is achieved through manual sexing, direct hormonal sex reversal, hybridisation, or genetic manipulation, has been proposed as a solution to the problem of early sexual maturation and unwanted reproduction. Hybridisation between various species of Oreochromis typically results in fertile all-male hybrids. Despite these developments, hybridisation did not effectively solve the problem of unwanted reproduction. This is mainly due to the difficulty of sustaining all-male hybrids’ production. This is most likely caused by insufficient care in keeping the broodstock segregated by sex and species and preventing the introduction of hybrids into the broodstock ponds. The masculinisation of the entire tilapia population through hormonal sex reversal by the addition of steroids to the food for a short period during the fry stage has been demonstrated to be an easily applied and relatively consistent technique for producing nearly all-male populations. However, this technique has yet to be fully accepted in some countries due to environmental and social constraints. For example, the effects of the degradation products of synthetic androgen on the environment still need to be fully understood in fish. A recently developed technique for obtaining monosex populations is the production of “supermales” through genetic manipulation. In a breeding program in O. niloticus , a technology was developed that produces genetically male tilapia with an average sex ratio of>95 % male and a 40 % increase in yield (GMT ®). This combines hormonal feminization of male fry, which are then crossed to normal (XY) males, producing ¼ XX, ½ XY, and ¼ YY. Males with the YY genotype only produce male (XY) offspring in crosses with normal females (XX). Further reading. Mair et al. 1997 (sex ratio); Eknath & Acosta 1998 (genetic methods); Guerrero & Guerrero-del Castillo 2002 ( Tilapia farming).

Oreochromis mossambicus ; aquarium stock, Germany; mouth-brooding female, ~ 150 mm SL. © A. Spreinat.

Oreochromis mossambicus ; aquarium stock, Germany; nuptial male, ~ 200 mm SL. © A. Spreinat.