Eggs and sperm are shed into the sea and their union is by chance. Depending on size, a female may shed from 50,000 to several million eggs over the spawning season. Fertilized eggs hatch in about 24 hours. The newly hatched larva is about 2.5 mm (0.098 in) long with a large yolk sack. Little is known about king mackerel in their first year of life. Yearling fish typically attain an average weight of 1.4–1.8 kg (3.1–4.0 lb) and a fork length of 60 cm (24 in). At age seven, females average 10 kg (22 lb), males 5 kg (11 lb). King mackerel may attain 40 kg (88 lb), but any over 7 kg (15 lb) is almost certainly a female.