What is the reproduction system of a piranha?

Piranhas reproduce through external fertilization, with most species engaging in seasonal spawning during the rainy season when water levels rise. Males typically establish territories to attract females, who lay eggs in nests made in the substrate. The male then fertilizes the eggs, which can number in the thousands, and both parents may guard the nest until the eggs hatch. After hatching, the young piranhas remain in schools for protection against predators.