This is how giants do
As noted in the short paper published in Coral Reefs:
On 10 August 2014 (full moon day, 0915 hrs, 25 m depth), a light color phase E. itajara released a sperm cloud (Fig. 1a, b). On 16 August 2014 (1430 hrs, 25 m depth), a different light color phase E. itajara released an egg cloud (Fig. 1c). Neither group spawning nor synchronized male–female spawning was observed.
The scientists posit that the light color phase of Goliath Groupers (Epinephelus itajara) may be an indicator that the fish is ready to spawn. Many fish change colors to signal they're ready to reproduce and now scientists and conservation groups may know what to look for when evaluating these critically endangered groupers.