Direct Ageing and Growth using Dorsal Fin Spines of Bluefin Tuna Thunnus thynnus (Scombridae) Reared in Sea Cages and a Comparison with Wild Populations

Abstract The main objectives of this study were to estimate the age and growth of reared Atlantic bluefin tuna and to reveal possible differences in growth between reared and wild specimens. A total of 806 specimens, ranging from 102 to 284 cm in length, were sampled from a Greek tuna farm in the Mediterranean Sea. The first spine of the first dorsal fin was used to estimate the age. Estimated ages ranged from 3 to 20 years, and the reproducibility of the ageing method was high. The proportion of the mean number of missing annuli per age due to vascularization ranged from 27.8 to 40.0%, with an average loss of 33.5%. No significant differences in the number of missing annuli were observed between 6–month and 18–month reared specimens of the same age group. The von Bertalanffy growth model was fitted a) to mean FL-at-age data and b) to mean RW-at-age data, and the growth equations found were: Lt = 296.6[1 – e(−0.114) (t + 1.026)] and Wt = 591.6[1 – e(−0.100)(t + 1.755)]3. Our results showed that the rearing process accelerates the growth of the Atlantic bluefin tuna and this was also evident in the calcified structure. In comparison with previous studies of growth in wild bluefin tuna from the Mediterranean Sea, mean weights at age of the reared fish were higher than those from wild fish in all age groups and lengths at age of the reared bluefin tuna were higher in younger fish, up to 6 years old.