The skipjack tuna is a biological machine built for constant, high-speed ocean travel.

Nature · Published 29 September 2026 Swipe more like this →

In short: With 68% of its body mass dedicated to locomotion, the skipjack tuna is the most muscular animal on Earth. This streamlined predator lacks a swim bladder, meaning it must swim continuously to stay buoyant. It is a global culinary staple, yet its survival faces modern environmental and industrial challenges.

The skipjack tuna (Katsuwonus pelamis) is a marvel of evolutionary engineering. As a cosmopolitan pelagic fish, it thrives in tropical and warm-temperate waters, often traveling in massive shoals of up to 50,000 individuals. Because it lacks a swim bladder, the skipjack is locked into a life of perpetual motion; it must swim constantly to maintain buoyancy. This relentless activity is supported by a unique physiology: it possesses the highest percentage of skeletal muscle devoted to movement of any animal species, accounting for 68% of its total body weight.

Commercially, the skipjack is a titan of the fishing industry. In 2018, global landings reached 3.2 million tonnes, making it the third-largest marine capture fishery. While its population is currently considered sustainable, the methods used to catch it—specifically purse seine nets—are subjects of ongoing debate due to concerns over bycatch. To address these ecological issues, some markets now label canned products by the specific fishing method employed. The species is also sensitive to broader environmental shifts, as climate change threatens to alter its distribution and catchability.

Beyond its role in industrial fishing, the skipjack is a vital cultural and culinary resource. Known as 'katsuo' in Japan, 'cakalang' in Indonesia, and 'aku' in Hawaii, it is prepared in diverse ways, from raw sashimi to smoked delicacies like katsuobushi. However, its position in the food chain carries risks. The fish is known to accumulate moderate levels of mercury and has been found to carry tributyltin (TBT), a toxic compound from ship hull paints. Studies have shown that about 90% of skipjack tested positive for TBT, particularly in Southeast Asia, highlighting the complex intersection between industrial pollution and global food security.

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