How do arapaima parents protect their developing young?

To protect their developing young, both parents of the Arapaima gigas (also known as the pirarucu) work together to excavate a spawning pit in the mud of shallow waters, using their lower jaws, fins, and mouths.12

Once the eggs are deposited and fertilized, the male guards the nest while the female remains nearby to ward off potential predators. After the embryos hatch—typically within seven days—the young congregate around the male’s head. During this period, the male’s head turns a dark, grayish-black color, which serves as camouflage for the young. This coloration, along with a potential chemical secretion from glands on the male's head, acts as a stimulus to keep the young grouped in a shoal. This parent-young association generally lasts for two to three months, after which the young are large enough to fend for themselves and the male’s head returns to its normal color.21