This study examines the anatomical development of Atlantic bluefin tuna during the first month of life at
histological level with emphasis in the gut development and those organs required to establish the hunting
behaviour characteristic of this species. The tuna larvae have been reared in mesocosm with copepods
(Acartia and Trigriopus sp.) as primary live prey during the first two weeks. The larvae hatched with 3.4
mm average TL and exhibited a very fast growth reaching between 4 and 5 cm at the end of the first
month. The yolk reserves were consumed rapidly in two days.