This is a cluster of eggs being tended to by an Anemonefish. A cluster is typically 300-700 eggs, which are laid and incubate near the anemone. They are then guarded by the male, who waves his fins to ventilate the eggs and “mouths” to transfer antibiotic substances to protect them against predation.
This is the really cool part. During incubation, chemicals from the anemone may penetrate the egg case and imprint the embryonic fish to the particular species of anemone.
Depending on species of anemonefish, eggs hatch in 4-7 days, usually at night. They will then become "planktonic", transported by the current, and find another anemone on which to settle.
