Histological evidence of Bluefin tuna (Thunnus thynnus Linnaeus, 1758) spawning in waters within the Mexican Exclusive Economic Zone in the Gulf of Mexico

Ovaries of bluefin tuna, Thunnus thynnus, from organisms measuring 247.62 ± 3.54 cm fork length collected within the Mexican Exclusive Economic Zone in the Gulf of Mexico, were examined. The highest gonadosomatic index was recorded in April (1.6 ± 0.28), coinciding with the presence of oocytes with a migratory nucleus (oocyte diameter 439 ± 32.84 µm); fully developed gonads were also observed in two females and two males (ovaries or testes, respectively) caught in late April when sea surface waters exceeded 26 °C. The microscopic examination of the gonads sampled showed structures that evidenced spawning in females measuring 280 cm FL.