California Fish Species

Blue Tilapia

• Scientific Name

  Oreochromis aureus
• Native

  Non-Native
• Identification

  

   

  • Deep, elongate, laterally compressed body
  • Cycloid scales, 16-23 along the first lateral line and 11-16 along the second
  • Bluntly pointed snout with a slightly oblique mouth that rarely extends past the outer margins of the eye
  • Females and non-breeding males are normally a pale gray to washed-out yellow with a series of bands on the sides
  • Spawning males have iridescent blue-gray heads with dark blue chins, bodies of pale blue, dorsal fins with a red border, and plain caudal fins with a pink upper margin
  • 14-17 spines and 9-14 rays on the dorsal fin
  • 1-3 spines and 7-12 rays on the anal fin
  • Truncate caudal fin
• Life History

   

  Blue tilapia can adapt to various habitats but are most commonly found in sloughs, backwaters, canals, and reservoirs. They are mostly a freshwater fish but can survive in salinities 2-3 times higher than that of sea water. They can also survive in water as cold as 5°C, lower than most other tilapia species can withstand. In California they feed primarily on aquatic plants and filamentous algae but in their native range they will also filter feed for zooplankton. Juveniles will prey on individual zooplankton until filtering becomes more energetically efficient.

  Sexual maturity for both sexes is reached when they have grown to between 10 cm and 18 cm, usually within their first year. Spawning occurs when a male claims a territory and digs a shallow pit for a nest. He then displays in front of the female school, convincing a female to follow him back to the nest. The pair will swim in circles before the female deposits her eggs onto the nest and then takes them into her mouth. The male responds by releasing his milt which the female in turn, takes into her mouth to fertilize the eggs. Once this fertilization is complete, the male chases that female away and begins displaying for another. The female incubates the eggs in her mouth until the young are free swimming and capable of being released into the water. The young stay with their mother for a few days after release during which time they can retreat to the safety of her mouth when a predator approaches. At the end of this period the young form massive schools in shallow water while the female returns to the school of females and may spawn again. Breeding can be repeated every 33-59 days. In their native lakes blue tilapia can grow to be 8-16 cm in their first year and 16-27 cm in their second reaching a maximum length of 37 cm and weight of 1 kg.

• Links to Other Research

  N / A
• Watershed

  N / A