The giant trevally, for example, grows to about 160 cm and 80 kg over
a lifespan of about 24 years and reaches reproductive maturity at
a length of about 60 to 95 cm when they are between 3 and 5 years
old. The smaller bluefi n trevally, which grows to 90 cm, reaches sexual
maturity at between 30 and 40 cm at an age of about 2 years.
Many species travel long distances to breed in large numbers (in
spawning aggregations). The areas at which they gather (spawning
sites) are often at the outer edge of fringing reefs or near reef passages.
These aggregations often occur as waters become warmer and at times
are related to the cycle of the moon.
During spawning, each female (~) releases many thousands of eggs
into the water and these are fertilised by sperm released by males
(|). The fertilised eggs hatch into very small forms (larvae) that drift in
the sea for periods often greater than a month. Less than one in every
thousand of the small fl oating forms survives to become a young fi sh
(juvenile).
When the drifting forms settle out as juveniles these may enter inshore
shallow water and move out to deeper reefs as they grow. Less than
one in every hundred juveniles survives the 2 to 5 years that it takes to
become a mature adult.