The Atlantic bluefin tuna mature at 4 years old in the east Atlantic and Mediterranean Sea, but it matures at 8 years old in the west Atlantic like the pacific and southern bluefin tuna. the length of the fish at maturity varies from east to west Atlantic, with east is 110–120 cm/30–35 kg and west is 200 cm/150 kg.
Bluefin tuna is a multiple spawning fish that spawn every year during the spawning season which is from mid-April to June. It spawns by eggs and the number of the eggs depends of the size and the age of the female. A 5 years old female produces about 5 million eggs compared to a 15–20 years female that can carry up to 45 million eggs. Fertilization of the eggs happens in the water and after two days of incubation without parental care, hatching happens.
The bluefin tuna larvae feeds on small zooplankton, but juvenile and adults feeds on a wide variety of prey and is able to adapt to whatever food becomes available. Bluefin tuna juveniles grow about 30cm per year which is slower than other tuna species. Then growth in length become less in adults than in juveniles, while growth in weight increases.
Bluefin tuna is a long-lived fish which means its natural mortality is low, and its higher during juvenile stages. Predation of bluefin tuna is from large pelagic sharks and killer whales. Bluefin tuna males are higher in fish nets than females and this causes lower growth for females.