The process of sexual reproduction for cod involves the act of spawning, resulting in the egg and sperm coming together for fertilization in open water. The male and female swim as a pair in circles during the spawning process.
A female cod can release between 3 million to 9 million eggs during a spawning season. The larger the female, the more eggs she produces each season, which lasts from January through April. Cod mate in the open sea in frigid waters with depths up to 660 feet. Their eggs, however, are very buoyant and float to the water's surface, where they are left unattended.
The fertilized eggs hatch in eight to 23 days, and very small larvae form. The cod larvae reaches a length of approximately 4 millimeters. During the first week of life, a cod larva lacks a fully developed mouth and relies entirely on an attached yolk sac for nutrition. Guided movement is also limited for a cod larva until the second to third week of life when it is able to use its fins for propulsion. Male cod reach sexual maturity between the ages of 2 and 4 years, while females reach sexual maturity between 5 and 6 years of age.