What physical trait is used to distinguish the white marlin's bill structure from that of the black marlin?

White marlins possess a relatively slender bill compared to the stouter, shorter bills seen on black marlins.

When comparing the morphology of the white marlin to the black marlin, the bill structure presents a clear difference reflecting distinct evolutionary pressures. The white marlin is equipped with a bill that is characterized as relatively slender. In contrast, the black marlin features a bill described as being stouter and shorter in proportion. This difference in bill morphology, coupled with the white marlin’s generally smaller overall size, suggests a specialized evolutionary path favoring agility and precision, likely for maneuvering against smaller, faster prey items such as schooling fish or squid often found in the upper pelagic zone, rather than relying on the sheer impact force associated with a bulkier structure.