Distinguishing between various marine species can be challenging, especially for large, fast-swimming predatory fish. Many share similar habitats and appearances, leading to frequent confusion and incorrect assumptions about their biological relationships. Understanding their unique characteristics is important for accurate identification.
The Definitive Answer
Marlins and tunas are distinct types of fish, belonging to entirely separate taxonomic families. Marlins are part of the Istiophoridae family, known as billfishes, which includes sailfish and spearfish. Tunas are classified within the tribe Thunnini, a subgroup of the Scombridae family, also known as the mackerel family.
Key Distinctions
Marlins and tunas exhibit several differences in their physical characteristics, behaviors, and diets. Marlins possess elongated bodies with a distinctive, spear-like upper jaw, or “bill,” which is rounded in cross-section. Their first dorsal fin is long and rigid, rising to a crest near the head, and they have large, forked tails. Blue marlins, for example, display a dark blue back fading to a silvery-white belly, often marked with vertical rows of blue spots.
Tunas, by contrast, have a sleek, torpedo-shaped body that tapers to a slender base before a crescent-shaped tail. They lack a prominent bill and instead have two dorsal fins, with a series of small finlets extending along their backs towards the tail. Tuna species are dark blue or black on their dorsal side and silvery below. Unlike most fish, tunas possess a unique circulatory system that allows them to maintain a body temperature higher than the surrounding water.
Both marlins and tunas are pelagic, inhabiting the open ocean, and are highly migratory. Marlins are solitary hunters, using their bills to stun or injure prey before consuming it. They feed on various pelagic fishes like mackerel, other tunas, and flying fish, as well as squid. Young marlins begin their diet with zooplankton, transitioning to larger prey as they grow.
Tunas are fast-swimming predators that form schools and hunt smaller fish like sardines, herring, mackerel, squid, and crustaceans. Some tuna species can dive to significant depths, even beyond 1,000 meters, though they remain closer to the surface. Blue marlin can grow over 16 feet long and weigh up to 1,800 pounds, with females being much larger than males. Atlantic bluefin tuna can also reach impressive sizes, growing up to 13 feet long and weighing as much as 2,000 pounds.
Why the Misconception?
The common confusion between marlins and tunas stems from several shared characteristics. Both are large, powerful, fast-swimming predators inhabiting the open ocean, found in similar tropical and subtropical waters. Their shared environment and similar lifestyles as apex predators can lead to their casual grouping by the public. Marlins also prey on tunas, indicating interaction within the marine food web.
Both fish are highly valued as game fish, making them popular targets for sport fishing. This shared popularity contributes to their frequent mention in media, blurring the lines for those without specific biological knowledge. Both marlin and tuna are also significant commercial seafood products, leading to their collective presence in markets and culinary discussions. This lack of detailed understanding about marine species contributes to the misconception that marlins and tunas are the same or closely related.