A study on oocyte development of the Atlantic bluefin tuna (Thunnus thynnus, Linnaeus 1758) under farming conditions

Body length and weight measurements and histological samples were collected from slaughtered Atlantic bluefin tuna (Thunnus thynnus) that were fattening under farming conditions for the determination of oocyte development in February 2015 (n = 10), May 2015 (n = 1), June 2015 (n = 1), July 2015 (n = 9), and July 2016 (n = 3) during harvest and soon after newly dead. The developmental phases of oocytes were evaluated based on their diameters, fork body length and weight of fish, surface water temperature, and species' reproduction season. According to the histological results, the oocytes were at the beginning of the regeneration and maturation phases in February; in the preovulation phase in May, advanced vitellogenic oocyte with yolk globules and atretic vitellogenic oocytes in June, and previtellogenic oocytes in July 2015. In July 2016, the oocytes were previtellogenic, vitellogenic, and advanced vitellogenic. Individuals were between 119 and 280 cm in fork length, weighed between 30 and 455 kg, and showed natural oocyte development at 16.7-22 degrees C surface water temperature under cage farming facility conditions during the species' natural spawning season of May, June, and July.