one thing i didn't notice that we do with mackerel- tuna and a number of other species here mark we bleed them . A large rubbermaid trash barrel filled with ice and salt water the ones we would keep we would cut across the main artery near head near pectoral fins a cut across each side of tail and suspend the tune in the ice / water in barrel tail tied to an old broom handle so they would bleed out. you will get a bit whiter filet and a milder flavor it will help slightly with skipjack. They are common in Sashimi and sushi, and make up the majority of the tuna that is canned for consumers , i like the stronger flavor next time out try bleeding one and another just do as normal and compare the the flavors and visual appearance of the two side by side.