This paper studies the growth and age of East Atlantic bluefin tuna based on the observation and analysis of hard parts (fin ray sections). The different parts and types of rings observed on the fin ray sections are defined. We concluded that: Hyaline rings are winter rings formed between fall and winter; Areas of active growth start forming in spring and ends their formation in the fall; For younger bluefin, in summer, size increases 3 to 4 times more and weight increases 4.5 to 6 times more than in winter; and Winter hyaline rings can be single (thin or thick) or double. From the growth equation obtained by combining data from the juvenile bluefin fishery of the Cantabrian Sea with that from the adult bluefin fishery of the Strait of Gibraltar area, a value of L aproximately equal to 318.35 cm is obtained, which corresponds to a W approximately equal to 615.90 kg.