How can you distinguish a female Atlantic bluefin tuna from a male externally?
José Antonio, from Isla Cristina, asked us: How can you distinguish a female Atlantic bluefin tuna from a male externally?
Patricia Reglero and Samar Saber from the Spanish Institute of Oceanography answered:
Gonads of adult Atlantic bluefin tuna specimens
A male and a female Atlantic bluefin tuna look exactly the same from the outside. But if we capture a specimen during the spawning season, at night, when the tuna lay their eggs, we can determine its sex by massaging its abdomen and seeing whether sperm or eggs come out. In the Mediterranean, the spawning season runs from June to July.