Skipjack Tuna are dark blue or purple on the back and silvery on their lower sides and belly. They have three to five prominent, dark longitudinal bands on their lower sides. These tuna have fine, slender teeth, a strong median keel on the caudal fin base between two small keels, and barely separated first and second dorsal fins.
Skipjack tuna are widespread in Australia's oceanic waters.
The global distribution of skipjack tuna includes all tropical and subtropical waters except for the eastern Mediterranean Sea and the Black Sea. However, adults are sometimes present waters as cold as 15 C. Skipjack tuna also need a dissolved oxygen level of 2.5 ml per 1 of sea water to maintain a minimum swimming speed and require higher levels when active. This requirement generally restricts skipjack tuna to water above the thermocline and in some areas, such as the eastern Pacific, may exclude them from surface waters. The depth range of skipjack tuna can be from surface waters to 260m during the day, but at night it is much shallower. Skipjack tuna are a schooling fish having a general tendency to school by size.